Beginners' sundialing course / North American Sundial Society

[Steve Lelievre]

NASS is pleased to announce the upcoming third instance of Elements of 
Dialing, our introductory course about sundials, their history, and the 
science that makes them work. The free 13-lesson course, intended for 
those are new to sundialing, runs from January 2024. The course 
coordinator will be Steve Lelievre, our Secretary and editor of NASS' 
journal, The Compendium. Steve will be assisted from time to time by 
other NASS officers.


The course is self-study, meaning written lessons are emailed out for 
course participants to work through in their own time. At the end of 
each lesson script there are a few questions which participants are 
expected to solve. One of these is a test question; the solution to it 
must be submitted to the course coordinator in order to receive the next 
lesson. To help things along, we schedule 'office hours,' conducted via 
Zoom videoconferencing. These optional sessions allow participants to 
discuss the lessons together and ask questions about the material.


The course is scheduled to start on January 6, 2024 and will normally 
operate on a 2-week cycle, although occasionally there will be three 
weeks between release of lessons.


To register, contact steve.lelievre.can...@gmail.com no later than 
December 16, 2023. Familiarity with basic geometry, algebra, and 
trigonometry at High School level is assumed. Membership in NASS is not 
required to join the course.


NASS acknowledges the efforts of Frans Maes, who developed the original 
Dutch course which inspired our version.


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Re: Re : Difference between types of equinox

[Steve Lelievre]

My thanks go to Bill and Hervé for responding to my equinox question.


The information they provided indicates that the change in definition of 
astronomical equinox, from delta = 0 to lambda = 0/180, had no practical 
impact as far as sundialing is concerned (only a few seconds). For the 
difference between astronomical equinox and temporal equinox, the French 
article recommended by Hervé explains the long-term drift of the 
solstices and astronomical equinoxes, and I now see the direct effect 
that phenomenon would have on temporal equinoxes (the midpoint between 
solstices.)



As well, I took Bill's hint and found a table of solstice and 
(astronomical) equinox dates and times for years 2001 to 2099. I used 
http://www.russellcottrell.com/blog/solarEvents.htm.  From the data I 
produced the enclosed graph of the time delay between the astronomical 
and the temporal equinox. Assuming I did the calculations right, then in 
the present day there are about 1.87 to 1.9 days between the two events. 
If we think in terms of whole days, those differences will correspond to 
one or two calendar days depending on when exactly each instant occurs 
within its day.



Cheers,

Steve









On 2023-09-05 2:23 a.m., Hervé Guillemet wrote:

Hi Steve,

I think that some answers to your questions can easily be found on the 
following link of the French "Institut de Mécanique Céleste et de 
Calcul des Éphémérides" (IMCCE) :

https://www.imcce.fr/newsletter/html/newsletter.html#current-article2
They publish (in French) a free information letter every month and in 
March and September it contains the timing of the equinox with a 
picture, easy to understand even if you do not speak French.


They remind that in the northern hemisphere the Autumn equinox is when 
the geocentric longitude of the Sun is exactly equal to 180° (and 0° 
for the Spring).  As indicated there is a difference of a few seconds 
with the time when its declination is equal to 0° and when its right 
ascension is equal to 12h.


The previous information letters can be accessed via :
https://www.imcce.fr/lettre-information/
and the data can be retrieved each March and September month

Best regards Hervé
----
*De: *"Steve Lelievre" 
*À: *"Sundial List" 
*Envoyé: *Mardi 5 Septembre 2023 01:23:15
*Objet: *Difference between types of equinox

Hello,

 From what I've read recently, there are three variants of an equinox:

- Modern astronomical definition: apparent geocentric longitude of the
sun is 0 or 180 degrees.

- The older astronomical definition (often used in dialling) : solar
declination is 0 degrees.

- 'Temporal equinox': halfway between solstices as measured by passage
of time, which is the lay/folk/traditional understanding

I'd like to know:

How big are the time intervals between these three types of equinoxes?

How much do these intervals change as the years or centuries go by, if
at all?

Thanks,

Steve




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Difference between types of equinox

[Steve Lelievre]

Hello,

From what I've read recently, there are three variants of an equinox:

- Modern astronomical definition: apparent geocentric longitude of the 
sun is 0 or 180 degrees.


- The older astronomical definition (often used in dialling) : solar 
declination is 0 degrees.


- 'Temporal equinox': halfway between solstices as measured by passage 
of time, which is the lay/folk/traditional understanding


I'd like to know:

How big are the time intervals between these three types of equinoxes?

How much do these intervals change as the years or centuries go by, if 
at all?


Thanks,

Steve




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World and Hour in Roman Minds

[Steve Lelievre]

Dear Dialists,

I seek an independent review of Richard J.A. Talbert’s recent book 
"World and Hour in Roman Minds: Exploratory Essays". All I've found 
online is the the publisher's summary, reproduced on various sites.


Can anyone steer me to a review source or, if you've read it yourself, 
give me an assessment of of the likely level of interest for a dialist 
with an interest in Roman-era time-keeping & measurement.


Thanks,

Steve





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Re: Seeking information on "F.G. Cheney"

[Steve Lelievre]

Hi,

Thanks!

Steve

On 2023-04-20 1:36 a.m., Hendrik Desmet wrote:

I found this:
"(...) Eight years later, Frank purchased *Cheney Foundry*, a small 
company in Minneapolis that poured aluminum and brass, from its 
retiring owner in 1963. Frank managed the foundry, and Lois managed 
the office.(...)

See https://carleyfoundry.com/about/history

Kind regards
Hendrik

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Re: Frank Cheney

[Steve Lelievre]

Excellent!

That'll be him.

Thanks very much,

Steve


On 2023-04-19 3:55 p.m., Patrick Vyvyan wrote:
This quote is from the North American Sundial Society description of a 
sundial in the Old Rose Garden of the Botanical Garden

University of California at Berkeley

"The armillary dial is made of red bronze and rests on a quarried 
stone pedestal. The equatorial ring includes hour lines with 15-minute 
marks and Roman numerals. It was created by Frank Cheney, a UC 
Berkeley graduate, Class of 1941, and later donated to the Garden by 
his family. Mr. Cheney was a civil engineer who developed a hobby of 
building sundials"


https://sundials.org/index.php/component/sundials/onedial/612

Probably the same person?

Best wishes,
Patrick Vyvyan

 
	Libre de virus.www.avast.com 
 




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Seeking information on "F.G. Cheney"

[Steve Lelievre]

Hello,

My question is mostly for dialists in the USA - can anyone tell me if 
there was a dial maker called Cheney (or a foundry that had dials in 
their product line) active in the early 1960s, possibly in the San 
Francisco area?


I'm trying to trace the origins of a 1961 dial that has "F.G.Cheney" 
cast into the underside.


Through Google I only found two businesses named F.G.Cheney. One is a 
quarry in Michigan and another that's a pharmacy in Ohio.


Thanks,

Steve

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Re: Adjusting dial to new location

[Steve Lelievre]

On 2023-04-08 8:52 p.m., Michael Ossipoff wrote:


I know you said you wanted a link, not instructions, but people have 
been suggesting how to achieve dial-autocorrection to Local True Solar 
Time (LTST) at the standard-meridian, instead of one’s own meridian. 
So I felt that it would be justified to comment about it.



Michael,

To me, your case seems to be a specific instance that is covered by the 
general case - have I missed something?


As things stand, I think I know the math involved because I have from 
the article by Fred Sawyer that I mentioned in a previous email. It 
describes the solution for the general case - we start with a dial at 
some latitude and longitude that shows the solar time at some other 
longitude, which may or may not be zero offset. We want to move it to a 
new latitude and longitude and to show the solar time at some new 
'other' longitude, which may or may not have zero offset from the new 
location. As well, the article by Fabio Savian, mentioned in his post, 
also discusses dial relocation. (BTW, for NASS members, Fabio only 
mentioned his article in its Italian version, but as well he kindly 
provided an English equivalent which was included in the most recent 
issue of the Compendium)


Everyone,

Since I'm writing this post, I'll take the opportunity to mention that I 
have made a couple of small adjustments to my online wedge calculator, 
gnomoni.ca/wedge . My thanks go to Roderick Wall for helping me make it 
better for the southern hemisphere. Please let me know if you spot any 
issues.


Steve


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Re: Adjusting dial to new location

[Steve Lelievre]

At a new location, a dial must end up with the style parallel to the 
polar axis - but how do you achieve that using a wedge? Assuming you 
start with the dial at the new location on a horizontal surface with the 
sub-stile line on the local meridian, the required sequence is to rotate 
it about the local vertical, then about an east-west line, and then 
about the vertical again. Perhaps this helps visualize it... 
https://youtu.be/mtEgSXJPXSw


The wedge achieves the same thing because the twisting of the dial on 
the wedge face corresponds to the first rotation about a vertical, it's 
tip angle corresponds to the east-west rotation, and the turning of the 
wedge corresponds to the second rotation about the vertical.


Steve


On 2023-04-04 11:59 a.m., Rod Wall wrote:


As Michael indicated in his email below: *Rotating the whole dial 
around the polar axis is the correct way. *to adjust a local solar 
time dial to a different longitude


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Re: Adjusting dial to new location

[Steve Lelievre]

Hi, Roderick,

My home internet connection is still non-functional so I can't fix it 
yet, but it does seem that I will have to add an extra test to handle 
southern hemisphere locations and reducing latitudes. Actually, I 
originally had a southern hemisphere check in there but took it out 
after convincing myself the same frame of reference (x axis east, y axis 
north, z up) applied to the spherical trigonometry irrespective of 
hemisphere. Ho hum.


Steve


On 2023-04-03 6:45 a.m., Rod Wall wrote:


Hi Steve,

For both examples below with all sundials at the same Longitude. The 
instructions indicate:


Place the wedge-sundial assembly on a horizontal surface in a nice 
sunny location. *Start with the higher end of the wedge to the north* 
and the sides aligned on a north-south line and the sharp edge should 
be on an east-west line.


Example 1:

If you have a sundial that was designed for Latitude -20 deg. And 
relocate it at Latitude -50 deg.


Would you start with the higher end of the 30 deg wedge to the North. 
Or would it be to the South?


*

Example 2:

If you have a sundial that was designed for Latitude 50 deg. And 
relocate it at 20 deg.


Would you start with the higher end of the 30 deg wedge to the North. 
Or would it be to the South?


*

Please correct me if I am wrong. I think that both examples would be 
to the South.


Roderick.

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Re: Adjusting dial to new location

[Steve Lelievre]

You don’t need two wedges, you just skew the positioning to do both
adjustments in one.

If you have The Compendium vol 7 issue 1, take a look at the articles by
Fred Sawyer and Bill Gottesman.

Steve

On Sun, Apr 2, 2023 at 17:20, Rod Wall  wrote:

> Hi Jack and Steve,
>
> To implement what Jack has indicated. You could have two wedges one on top
> of each other. One for Latitude correction and one for Longitude correction.
>
> You could also just use a Longitude correction wedge if you only wanted to
> correct for Longitude.
>
> When writing instructions. Please also include people who live in the
> southern hemisphere, we do also have sundials.
>
> Do I have this correct?
>
> Roderick.
>
> On 3/04/2023 9:24 am, Steve Lelievre wrote:
>
> Jack,
>
> Try out my calculator! You can specify a time zone meridian for the dial
> at its original location, or at its new location, or both. If there is an
> effective longitude change, it'll tell you how to position (twist) the dial
> on the wedge and how to orient the wedge itself, turning it away (rotating
> it ) from the meridian line.
>
> Steve
>
>
> On 2023-04-02 3:59 p.m., Jack Aubert wrote:
>
> I thought about this briefly.  I had always thought that the purpose of
> the shim or wedge adjustment was to tip the dial north or south so that
> dial is at the latitude it was originally designed for.  If the original
> dial has a built-in longitude correction, that could also be factored into
> a wedge which would have both a north-south and east-west axis.  But a
> wedge would not work if it moved the gnomon out of alignment with the with
> the rotation of the earth (or the celestial sphere).  I think a
> longitudinal adjustment would only work if he original dial had a time-zone
> offset included by rotating the hour lines with respect to the origin of
> the gnomon.
>
>
>
> Does this make sense?  It sounds like a good project for a 3-D printer.
>
>
>
> Jack
>
>
>
> *From:* sundial 
>  *On Behalf Of *Steve Lelievre
> *Sent:* Sunday, April 2, 2023 5:16 PM
> *To:* Michael Ossipoff  
> *Cc:* Sundial List  
> *Subject:* Re: Adjusting dial to new location
>
>
>
> Michael,
>
> Yes, I recognize that to get Mean Time involves Equation of Time
> adjustment and that Equation of Longitude can be handled there to give
> Standard Time (or DST).
>
> But anyway, my inquiry was to seek an online wedge calculator. Nobody
> identified one and  a week seemed an adequate wait for responses, so I've
> just written one.  Anyone who's interested, please see
>
>
> https://sundials.org/index.php/teachers-corner/sundial-construction/367-easy-dial-adjustment-for-your-latitude
>
> Cheers,
>
> Steve
>
>
>
> On 2023-04-02 1:41 p.m., Michael Ossipoff wrote:
>
> I just want to mention that the shim under the north or south edge of the
> dial is only for latitude. Longitude is corrected-for by changing the
> constant term of the Sundial-Time to Clock-Time conversion.
>
>
>
> But usually Sundial-Time, Local True Solar Time, is what I’d want from a
> sundial.
>
>
>
> On Sun, Mar 26, 2023 at 14:30 Steve Lelievre <
> steve.lelievre.can...@gmail.com> wrote:
>
> Hi,
>
> Can anyone point me to an existing online calculator for making a wedge
> to adjust a horizontal dial to a new latitude and longitude?
>
> I am not asking for an explanation of how to do the calculation; I just
> want to be able to point people to a calculator that has already been
> proved on the internet. It should use the original location (latitude
> and longitude) and the new location to calculate the angle of slope of
> the wedge and the required rotation from the meridian.
>
> Many thanks,
>
> Steve
>
>
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>
>
> ---https://lists.uni-koeln.de/mailman/listinfo/sundial
>
> --
Cell +1 778 837 5771
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Re: RE: Adjusting dial to new location

[Steve Lelievre]

Jack,

Try out my calculator! You can specify a time zone meridian for the dial 
at its original location, or at its new location, or both. If there is 
an effective longitude change, it'll tell you how to position (twist) 
the dial on the wedge and how to orient the wedge itself, turning it 
away (rotating it ) from the meridian line.


Steve


On 2023-04-02 3:59 p.m., Jack Aubert wrote:


I thought about this briefly.  I had always thought that the purpose 
of the shim or wedge adjustment was to tip the dial north or south so 
that dial is at the latitude it was originally designed for.  If the 
original dial has a built-in longitude correction, that could also be 
factored into a wedge which would have both a north-south and 
east-west axis.  But a wedge would not work if it moved the gnomon out 
of alignment with the with the rotation of the earth (or the celestial 
sphere).  I think a longitudinal adjustment would only work if he 
original dial had a time-zone offset included by rotating the hour 
lines with respect to the origin of the gnomon.


Does this make sense?  It sounds like a good project for a 3-D printer.

Jack

*From:* sundial  *On Behalf Of *Steve 
Lelievre

*Sent:* Sunday, April 2, 2023 5:16 PM
*To:* Michael Ossipoff 
*Cc:* Sundial List 
*Subject:* Re: Adjusting dial to new location

Michael,

Yes, I recognize that to get Mean Time involves Equation of Time 
adjustment and that Equation of Longitude can be handled there to give 
Standard Time (or DST).


But anyway, my inquiry was to seek an online wedge calculator. Nobody 
identified one and  a week seemed an adequate wait for responses, so 
I've just written one.  Anyone who's interested, please see


https://sundials.org/index.php/teachers-corner/sundial-construction/367-easy-dial-adjustment-for-your-latitude

Cheers,

Steve

On 2023-04-02 1:41 p.m., Michael Ossipoff wrote:

I just want to mention that the shim under the north or south edge
of the dial is only for latitude. Longitude is corrected-for by
changing the constant term of the Sundial-Time to Clock-Time
conversion.

But usually Sundial-Time, Local True Solar Time, is what I’d want
from a sundial.

On Sun, Mar 26, 2023 at 14:30 Steve Lelievre
 wrote:

Hi,

Can anyone point me to an existing online calculator for
making a wedge
to adjust a horizontal dial to a new latitude and longitude?

I am not asking for an explanation of how to do the
calculation; I just
want to be able to point people to a calculator that has
already been
proved on the internet. It should use the original location
(latitude
and longitude) and the new location to calculate the angle of
slope of
the wedge and the required rotation from the meridian.

Many thanks,

Steve


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Re: Adjusting dial to new location

[Steve Lelievre]

Michael,

Yes, I recognize that to get Mean Time involves Equation of Time 
adjustment and that Equation of Longitude can be handled there to give 
Standard Time (or DST).


But anyway, my inquiry was to seek an online wedge calculator. Nobody 
identified one and  a week seemed an adequate wait for responses, so 
I've just written one.  Anyone who's interested, please see


https://sundials.org/index.php/teachers-corner/sundial-construction/367-easy-dial-adjustment-for-your-latitude

Cheers,

Steve


On 2023-04-02 1:41 p.m., Michael Ossipoff wrote:
I just want to mention that the shim under the north or south edge of 
the dial is only for latitude. Longitude is corrected-for by changing 
the constant term of the Sundial-Time to Clock-Time conversion.


But usually Sundial-Time, Local True Solar Time, is what I’d want from 
a sundial.


On Sun, Mar 26, 2023 at 14:30 Steve Lelievre 
 wrote:


Hi,

Can anyone point me to an existing online calculator for making a
wedge
to adjust a horizontal dial to a new latitude and longitude?

I am not asking for an explanation of how to do the calculation; I
just
want to be able to point people to a calculator that has already been
proved on the internet. It should use the original location (latitude
and longitude) and the new location to calculate the angle of
slope of
the wedge and the required rotation from the meridian.

Many thanks,

Steve


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Adjusting dial to new location

[Steve Lelievre]

Hi,

Can anyone point me to an existing online calculator for making a wedge 
to adjust a horizontal dial to a new latitude and longitude?


I am not asking for an explanation of how to do the calculation; I just 
want to be able to point people to a calculator that has already been 
proved on the internet. It should use the original location (latitude 
and longitude) and the new location to calculate the angle of slope of 
the wedge and the required rotation from the meridian.


Many thanks,

Steve


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Re: What is purpose of the shaded area on the face of this sundial in Agra?

[Steve Lelievre]

Bill,

On 2022-12-09 4:06 p.m., Bill Gottesman wrote:
The side of the trapezoid between12:00 and 1:00 skews to the 1:00 line 
- I have doubts that it was intended to track to the origin.  Whatever 
that means.


Well spotted.

On a copy of the dial face, I drew in the hour lines extended back 
towards the centre. Most of them convert at a point consistent with the 
knife-edge style that can be seen on the gnomon; likewise the hour lines 
for the hours closest to noon are slightly offset in a way that would be 
expected from the secondary styles created by the bevelled edges of the 
wide gnomon.


So, the dial was crafted quite precisely. The sides of the grey area 
don't match that precision, which supports your suggestion that it is a 
repair.


Cheers,

Steve

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Re: No more leap seconds!

[Steve Lelievre]

Ah, the joys of Listservs and email software. My participation sometimes 
gets of of step too: occasionally, original posts reach me after other 
people's replies.


Perhaps it wouldn't be a problem if all the world's computers were 
exactly synchronized... perhaps they could use atomic clocks for that   ;-)


Cheers,

Steve


On 2022-11-21 12:04 a.m., John Pickard wrote:


Sorry Steve,

I sent my post before seeing yours.

--
Cheers, John.

Dr John Pickard.
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No more leap seconds!

[Steve Lelievre]

Apparently the Powers That Be have officially decided that Clock Time is 
right and Solar Time is wrong.


Or to put it another way, the International Bureau of Weights and 
Measures has voted to stop using Leap Seconds by by 2035.


However, an IBWM representative said "the connection between UTC and the 
rotation of the Earth is not lost [...] Nothing will change [for the 
public]" which apparently means we'll have less frequent adjustments 
instead (leap minutes?).


https://phys.org/news/2022-11-global-timekeepers-vote-scrap.html

Steve


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Re: How to turn ecliptic longitude into solar declination?

[Steve Lelievre]

Michael,

On 2022-10-16 1:40 p.m., Michael Ossipoff wrote:
Thank you for mentioning that I answered Steve's question.   
...something not acknowledged by Steve for some reason.


Please be assured that no slight was intended. Thank you for taking the 
time to reply to my question.


I did not acknowledge your response because I had not seen it. My email 
software treated your messages as spam so I didn't see them until 
Frank's message prompted me to check the junk folder. Just as soon as I 
figure out the applicable setting, I'll change it.


Steve


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Re: How to turn ecliptic longitude into solar declination?

[Steve Lelievre]

My thanks go Werner for his detailed and helpful response to my 
question, and Fabio for his interesting comments on the astrolabe.


I learned some new things today, and it was nice to see a diagram of the 
offset circles on the back of the astrolabe. Clever.


Cheers,

Steve


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How to turn ecliptic longitude into solar declination?

[Steve Lelievre]

Hi,

For a little project I did today, I needed the day's solar declination 
for the start, one third gone, and two-thirds gone, of each zodiacal 
month (i.e. approximately the 1st, 11th and 21st days of the zodiacal 
months).


I treated each of the required dates as a multiple of 10 degrees of 
ecliptic longitude, took the sine and multiplied it by 23.44 (for 
solstitial solar declination). At first glance, the calculation seems to 
have produced results that are adequate for my purposes, but I've got a 
suspicion that it's not quite right (because Earth's orbit is an 
ellipse, velocity varies, etc.)


My questions: How good or bad was my approximation? Is there a better 
approximation/empirical formula, short of doing a complex calculation?


Cheers,

Steve





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Seeking photo of sundial with analemma-like shadow positions

[Steve Lelievre]

Hi,

I'm seeking a composite photo that shows the seasonal variation in the 
mean time position of the shadow on a dial face - equivalent to a sky 
analemma photo but based on the shadow.


Ideally, the photo would involve a plane dial with a nodus to produce a 
distinct figure-8 track.


Any help appreciated.

Steve


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Re: Computing hour lines for horizontal sundials

[Steve Lelievre]

Hi,

Actually, I understood that the tables come with 10 already added.

I saw the advantage of having tables of logs of trig values but I have 
struggled to understand the advantage of adding 10 to the values in the 
table. When I compare that to using the logs directly, it seems more 
complicated in that one has to subtract some multiple of ten from the 
sum of the values taken from the table (1 x 10 when multiplying two 
values, 2 x 10 when multiplying three values, etc.) My thinking was that 
if the aim was to simply to avoid using negatives, the calculator-person 
could simply leave off the minus sign.


But now, from looking again at the examples in your diagram, I think I 
understand: it seems that one does not carry digits over into the tens 
column of the summation. And dropping the tens column has the same 
effect as subtracting the extra multiples of 10.


So, for example, the method involves something along the lines of 9.1 + 
9.1 + 9.1 = 27.3 but don't write '2' in the tens column  = 7.3.


It's nice to encounter so many strange things on the Sundial List.

Steve




On 2022-08-09 1:12 p.m., R. Hooijenga wrote:


Hi Steve, all,

Yes, the ’10-trick’ was so common because it made things very easy – 
well, comparatively speaking.


But I see I have not been entirely clear: I forgot to mention the big 
trick, because to me it is so obvious – the user doesn’t have to do 
any adjusting, because the tables list everything ready-made.


For instance, the sines table would not tabulate sines, nor would it 
tabulate the log of sines: it would tabulate the ten plus the log of 
the sine.


All the computer (the person doing the computing!) had to do was look 
up the angle – say, 31° 25’ from the example – and get the number 
9.71705 /directly from the SIN table/. Likewise, 45° 05’ will give you 
9.84885 in the COS table.


The addition of ‘minus ten’ in the example below was just to make it 
clear to me, the student, what was happening. In actual practice it 
was never written down.


And going the other way, still in the example below, you could just 
search for ‘9.88400’ in the log-sin table and find the corresponding 
angle 49°57’ 36”. (Unfortunately, there is a printer’s error in the 
example here: the number should really be 9.88400 , not 0.88400.)


Of course, interpolation was most always required; there were handy 
small lists for that in the margins of the table pages.


/A sight reduction form was a marvel of efficiency/. Just take your 
sextant-read altitudes, determine all necessary corrections (you must 
do all that even today), and enter all on the form.


Then, just proceed line by line: adding, sometimes subtracting, and 
looking up in tables; and you end up with a star fix.


Later, we got the HO-249 (and similar) publications, reducing the work 
even further. I bet that old first mate could work out a fix just as 
fast as anyone can today on an iPad.


And if we dropped our HO-249, the worst that could happen was that we 
cracked the spine (not that it ever happened); compare that to the 
drama that a falling iPad might engender!


Rudolf

*Van:* sundial  *Namens *Steve Lelievre
*Verzonden:* dinsdag 9 augustus 2022 17:43
*Aan:* sundial@uni-koeln.de
*Onderwerp:* Re: Computing hour lines for horizontal sundials

Ooof!

Did the method of adjusting all the logs by +10 really make the task 
easier?


Merely negating the log seems better to me or simply learning to 
do arithmetic on negatives.


Steve
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Re: Computing hour lines for horizontal sundials

[Steve Lelievre]

Ooof!

Did the method of adjusting all the logs by +10 really make the task easier?

Merely negating the log seems better to me or simply learning to do 
arithmetic on negatives.


Steve


On 2022-08-09 8:11 a.m., R. Hooijenga via sundial wrote:



Frans' answer is much to the point here.

When I started at sea, star fixes were computed on a sight reduction 
form. Without the benefit of a calculator, it would be folly to 
attempt this without logarithms. (At the time, I did have a brand-new 
Sinclair Scientific, but the first mate took a dim view of this 
new-fangled contraption.)


To avoid the negatives, 10 was added, only to be dismissed after the 
addition or subtraction.


The example below is from W.L. Kennon: /Astronomy/, which I kept from 
freshman year. It shows the use of logarithms and of the ‘10’.


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Re: Recording of NASS Zoom meeting, Lesson 9

[Steve Lelievre]

Oh dear. My message from earlier today was was not meant to go to the 
sundial list.


My apologies,

Steve


On 2022-05-14 3:17 p.m., Steve Lelievre wrote:

Hello everyone,

I have uploaded the video recording of today's NASS Zoom meeting, the 
review for Lesson 9.


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Recording of NASS Zoom meeting, Lesson 9

[Steve Lelievre]

Hello everyone,

I have uploaded the video recording of today's NASS Zoom meeting, the 
review for Lesson 9.  Please note that I have edited out several minutes 
near the start of the video during which we were distracted by some 
connectivity issues. You will find the video for download at 
https://www.dropbox.com/s/k54pdnws65ksolk/LessonReview.mp4?dl=1


To play it directly from the server, try using 
https://www.dropbox.com/s/k54pdnws65ksolk/LessonReview.mp4?dl=0 (no need 
to create / login a Dropbox account, just cancel the pop-up that invites 
you to create an account)


The video will remain available for at least 72 hours from the time of 
this message, but I will likely delete it fairly soon after that.


Regards,

Steve





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U.S. Senate approves bill to make daylight saving time permanent

[Steve Lelievre]

It seems the USA may be getting ready to abolish seasonal clock 
changes.  The proposal has just passed in the Senate but still has to be 
accepted by the House of Representatives, so we can't celebrate yet. ( 
https://www.reuters.com/world/us/us-senate-approves-bill-that-would-make-daylight-savings-time-permanent-2023-2022-03-15/ 
)


If it happens, Canada would quickly follow. In fact, here in British 
Columbia it's already in law that we will switch to permanent DST once 
Washington (state), Oregon and California have switched. The EU is 
already on the same path but things have got bogged down with some 
member countries yet to decide which timezone to adopt. EU-wide 
preparations were further delayed due to the pandemic ( 
https://www.thelocal.it/20211029/clocks-to-go-back-in-italy-despite-eu-deal-on-scrapping-hour-change/ 
).


I would have preferred permanent Standard Time over permanent 
Daylight-saving Time but, even so, I hope the plans proceed. It will 
certainly simplify the my designs for Civil Time sundials and Equation 
Of Time signage.


Cheers, Steve

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Re: Telling time with a rope?

[Steve Lelievre]

Hi everyone,

Regarding the presentation mentioned by Roger, I found that Stephen 
Luecking had a paper in The Compendium: "Laying Out A Sundial Using 
Ancient Rope Geometry" / Stephen Luecking / The Compendium 12(4), 
December 2005, pp.5-9. As well, he discussed using rope for constructing 
layouts, but not related to sundials, in "Pulling Ropes and Plumbing 
Lines: Geometry for the Neolithic Engineer," available on the web at 
https://archive.bridgesmathart.org/2004/bridges2004-321.pdf


Further to Jack's note, with one common meaning of 'pommel' in English 
being the knob at the end of a sword handle, it's easy to see relating 
to any knob at the end of a rod, then one just has to look at an 
armillary sphere to see how that can transfer that meaning to a 
celestial pole.


Steve
Terrestrial Armillary Sphere - Historic Models, Authenic Museum Replicas 
and Furniture






On 2022-03-04 8:57 a.m., Roger Bailey wrote:
At the NASS conference in 2005 in Chicago, Stephen Luecking gave a 
Rope Geometry Workshop, "Laying Out a Sundial on the Landscape Using 
Ancient Rope Geometry".This was based on his paper "Rope Geometry: 
History and Methods" These described other methods for telling time 
with rope,different from Marchants . People used what they had at hand.


Roger Bailey

On Thu, Mar 3, 2022 at 11:45 AM Jack Aubert  wrote:

I tired searching for “pommeau de ciel” and “pommeau des cieux”,
which not surprisingly I did not recognize in either English or
French. Pommel is Pommeau in French.  I mostly got hits for shower
heads and gear shift knobs… but did find a reference to the
original French on Google Books:


https://books.google.com/books?id=BVtcMAAJ=PA108=PA108=pommeau+de+ciel=bl=4NKJk6haHD=ACfU3U0xr9oORL7S6zs-nKRg-NnTizDKfQ=en=X=2ahUKEwiD_trVyqr2AhVlkeAKHacJDbwQ6AF6BAghEAM#v=onepage=pommeau%20de%20ciel=false

<https://books.google.com/books?id=BVtcMAAJ=PA108=PA108=pommeau+de+ciel=bl=4NKJk6haHD=ACfU3U0xr9oORL7S6zs-nKRg-NnTizDKfQ=en=X=2ahUKEwiD_trVyqr2AhVlkeAKHacJDbwQ6AF6BAghEAM#v=onepage=pommeau%20de%20ciel=false>

But reading the text, it does appear that “pommel of the sky”
could only refer to Polaris, as Steve surmises.  That being said,
I have to suspect that Guy Marchant came up with this method, that
would be beyond the interest the vast majority of shepherds, on
his own.  A shepherd, who is probably illiterate, is supposed to
identify a star and remember to adjust its time position
throughout the year?  Also, why would he care what time it is at
night?  Maybe they taught that in advanced shepherd class.

Jack

*From:* sundial  *On Behalf Of
*Steve Lelievre
*Sent:* Thursday, March 3, 2022 2:17 PM
*To:* sundial@uni-koeln.de
*Subject:* Re: Telling time with a rope?

Hi,

 I think the pommel of the sky refers to the celestial north pole,
i.e. where we see the Pole Star or Polaris.

Then, on the summer solstice hold a plumb line in front of you
such that it obscures the Pole Star, and find another circumpolar
that is also hidden by the plumbline.  In the rest of the year,
the angular displacement of this second star tells you how far
from midnight you are, provided you make an adjustment of 1 hour
per half month.

For the method to work, you need to have established midnight on
the summer solstice. This is done by fixing two plumb lines one
behind the other, so that they are aligned to the solstice's
midday sun, i.e. they show you the meridian. I think the text is
saying that on the day of the summer solstice, as the shepherd
faces north looking through the plumb lines, if Cancer is seen
slightly to the east and Capricorn slightly to the west, then it
is midnight (presumably that's only in the British Isles).

I got this  from a rather quick scan of the text, so I may have
missed something. There's also discussion of the learning the
rising positions of the signs of the zodiac but I don't quite
follow how it relates to the rest.

Steve

On 2022-03-03 10:11 a.m., Dan-George Uza wrote:

Hello,

In the "Kalendar and Compost of Shepherds" by Guy Marchant, an
illustrated work translated from French into English in the
early 1500s, there is a chapter with the following title:
"Shepherds practise their quadrant at night as you see by the
figure hereafter". Could someone more versed in old English
please explain how this technique actually worked? I attach
the relevant pages from the 1931 edition.

Thanks,

-- 


Dan-George Uza


<https://www.avast.com/sig-email?utm_medium=email_source=link_campaign=sig-email_content=webmail>



Virus-free. www.avast.com

<https://www.avast.co

Re: Telling time with a rope?

[Steve Lelievre]

Hi,

 I think the pommel of the sky refers to the celestial north pole, i.e. 
where we see the Pole Star or Polaris.


Then, on the summer solstice hold a plumb line in front of you such that 
it obscures the Pole Star, and find another circumpolar that is also 
hidden by the plumbline.  In the rest of the year, the angular 
displacement of this second star tells you how far from midnight you 
are, provided you make an adjustment of 1 hour per half month.


For the method to work, you need to have established midnight on the 
summer solstice. This is done by fixing two plumb lines one behind the 
other, so that they are aligned to the solstice's midday sun, i.e. they 
show you the meridian. I think the text is saying that on the day of the 
summer solstice, as the shepherd faces north looking through the plumb 
lines, if Cancer is seen slightly to the east and Capricorn slightly to 
the west, then it is midnight (presumably that's only in the British Isles).


I got this  from a rather quick scan of the text, so I may have missed 
something. There's also discussion of the learning the rising positions 
of the signs of the zodiac but I don't quite follow how it relates to 
the rest.


Steve







On 2022-03-03 10:11 a.m., Dan-George Uza wrote:

Hello,

In the "Kalendar and Compost of Shepherds" by Guy Marchant, an 
illustrated work translated from French into English in the early 
1500s, there is a chapter with the following title: "Shepherds 
practise their quadrant at night as you see by the figure hereafter". 
Could someone more versed in old English please explain how this 
technique actually worked? I attach the relevant pages from the 1931 
edition.


Thanks,

--
Dan-George Uza

 
	Virus-free. www.avast.com 
 




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Re: What does 'hectemoros' mean, as in Hectemoros Angle?

[Steve Lelievre]

Thank you to everyone who responded, on or off list, to my inquiry about 
the etymology of the word 'hectemoros'. I've learned that it is a Greek 
word meaning 'one sixth part', i.e. the fraction 1/6 (hect- comparable 
to the prefix hex- in hexagon.). That easily explains why the serfs I 
mentioned in my question were the hectemoroi : they were the 'one-sixth' 
people because of the rents they had to pay.


The term as used in gnomonics refers to either the angle between the 
current position of the sun and either the east and west points of the 
local horizon, or the great circle through those same points. Why 
hectemoros?


Apparently it was named as such by Ptolemy for his version of the 
analemma (analemma in the archaic sense of a projection). The great 
circle in question gets projected as a straight line that when divided 
in 6 parts represents the 6 hours between noon and dawn or dusk - thus 
it is the line of sixths, and from that the great circle that mapped to 
the line became the hectemoros circle.


Thanks again,

Steve








I'm looking for an etymological explanation of the word 'hectemoros' as
used in gnomonics for the direct angle between the East (or West)
Cardinal Point and the current position of the sun on the celestial 
sphere.


I have scoured the Internet but the only meaning I can find relates to a
class of person in ancient Greece - serfs who paid one sixth of their
income as rent. Thanks in advance for information about the derivation
as it relates to dialing.





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What does 'hectemoros' mean, as in Hectemoros Angle?

[Steve Lelievre]

Hi,

I'm looking for an etymological explanation of the word 'hectemoros' as 
used in gnomonics for the direct angle between the East (or West) 
Cardinal Point and the current position of the sun on the celestial sphere.


I have scoured the Internet but the only meaning I can find relates to a 
class of person in ancient Greece - serfs who paid one sixth of their 
income as rent. Thanks in advance for information about the derivation 
as it relates to dialing.


Regards,

Steve





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Purpose of circular decorative patterns on some New England pewter dials

[Steve Lelievre]

Hi everyone,

Following on from my recent post asking about the method of manufacture 
of early New England pewter dials, now I have a question about a pattern 
that appears on several examples.


The following links are all photos of different dials and yet they all 
share a set of circles inscribed in the middle of the dial. There are 
loads of other examples in Google Images (but to confuse things, some 
may be modern reproductions).


The theme that I refer to is the set  of concentric circles that seem to 
be centred about half way between the centre of the dial face and the 
toe of the gnomon. There are are usually 3 or 4 circles, but sometimes 
more, Outside them is an arc, with a different centre, which has its two 
ends touching the outermost of the concentric circles so that it 
outlines a lune.


Is there some significance to these circles and arcs?

Is it just a case of makers copying/stealing designs? (Josiah Miller 
seems to be the preeminent maker using these features and his examples 
are quite fine, so perhaps there was a market for cheaper knockoffs).


Thanks,

Steve


Maker "D.L": 
https://www.freemansauction.com/auction/lot/34-pewter-sundial/?lot=441293=1


Maker unknown: https://images.nypl.org/index.php?id=1160659=w

Maker unknown: https://www.skinnerinc.com/auctions/3278M/lots/451

Maker "Josiah Miller": 
https://thumbs.worthpoint.com/zoom/images1/1/1212/23/wonderful-18th-early-american-pewter_1_ddfc0b18e848cd4e170fed601710a3b2.jpg


Maker "Josiah Miller": https://www.metmuseum.org/art/collection/search/8027

Maker "Michael Ryan": https://www.antiquepewtershop.com/item-9862

Maker unknown: 
https://www.freemansauction.com/auction/lot/36-small-pewter-sundial/?lot=441297=4547 
(many rings, no lune)










///workers.exist.lookout

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Re: A mis-aligned vertical dial

[Steve Lelievre]

John,

Unfortunately, I can't direct you to an existing tabulation of the 
alignment errors on a vertical dial.


However, I do have a comment regarding your subordinate question about 
average errors: in my experience of the world of work, it is always a 
good thing to arrive on time or a little early for meetings, being a 
minute or two late is accepted, but we are sure to earn a frown when we 
are more than about 5 minutes late. So back in the era when I would have 
used a sundial to organize my day, I feel sure that knowing the maximum 
error would have been as important, if not more so, as knowing the 
average error. As well, I do not think that the simple average is 
particularly helpful because sometimes the dial will be early and 
sometimes late - the result can still be near zero. Instead, I would 
have wanted to know the average lateness.


There have been a few times when I've written software to optimize dial 
layouts for least error. I usually do it by minimizing the worst case error.


But then again, I'm a crank.

Steve

P.S. As an aside, for a horizontal dial, The Compendium carried a series 
of detailed articles from 1995 to 1997,  under the title 'Error Analysis 
Of The Horizontal Sundial' / T.J. Lauroesch, J.R. Edinger





On 2021-11-08 5:38 a.m., John Foad wrote:


If a vertical dial is relocated and now faces a few degrees east or 
west of its designed declination, you might expect it to run a few 
minutes slow or fast.  Has anyone ever tabulated the greatest error, 
and at what times and dates it occurs?  And does it make sense to 
think about the average error?  Clearly the errors depend on the 
latitude and the design declination, but for starters they could be 
tabulated just for a direct south dial at 52.5 degrees N,  and for a 
location move of 1, 2 and 5 degrees either way.  As the gnomon is no 
longer polar-pointing I imagine the maths is a bit hairy.


Best wishes,

John Foad


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Re: What's the inner scale on this photo for?

[Steve Lelievre]

Thank you, Sara and Patrick for your replies to my question.

I shall try to get to the Science Museum sometime to have a look at the
dial, if that can be arranged.

I’ve been trying to figure out how the cam that Sara mentioned might work.

I’ve never studied the working of cams and this case isn’t obvious to me as
there are two inputs, azimuth and declination, that must drive the minutes
shown.

If anyone can send me an explanation or drawing, it would me much
appreciated.

Steve

On Mon, Oct 25, 2021 at 19:19, Schechner, Sara 
wrote:

> Hi Steve,
> The photo of the azimuth dial is hard to read.  I don't know what screws
> you are talking about preventing the arm from turning.  The arm is
> backwards at the moment since the pointed end should be on the scale of
> hour lines.  I am not convinced that there is a flap on the square end of
> the arm for a vane.  The sun at most angles would not fall far along the
> arm to reach the other end where the slot is.  Rather, I suspect there was
> a vertical gnomon in the slot at the pointed end.  Its shadow could have
> been aligned with the point so that the point was in line with the sun's
> azimuth.  As for the round dial, it almost always shows minutes and is
> geared to the rotation of the arm.
>
> That's my best guess.
> Sara
>
> -Original Message-----
> From: sundial  On Behalf Of Steve Lelievre
> Sent: Monday, October 25, 2021 1:22 PM
> To: Sundial List 
> Subject: What's the inner scale on this photo for?
>
> Hi,
>
> Today a website called Vermont Free Press published an appallingly
> confusing (to me) summary of types of sundials. If you can bear to look,
> it's at https://www.vermontpressbureau.com/types-of-sundials/
>
> However, there was one thing about it that piqued my interest: the photo
> of an azimuth sundial (
> https://www.vermontpressbureau.com/wp-content/uploads/2021/10/Azimuthal.jpg
> ).
>
>  From what I can make out, there is a metal flap at the end of the alidade
> / sighting arm (the end at top in the photo). It must get turned up to make
> a shadow-caster.  I guess the arm has to be rotated so that the shadow
> falls along it, and time is then read from where the right-hand edge of the
> arm crosses the net of hour and declination lines. But then, wouldn't the
> screws seen in the upper plate block the arm from being turned to the
> required orientation?
>
> Another bit I can't figure is the little circular scale just north of the
> centre of the dial, with the pointer. Perhaps just an Equation of Time
> scale? Or perhaps a cam connects it to the arm so that it can be used to
> set the arm's length? (The slot in the arm suggests it can be slid in and
> out to set the tip at the applicable declination circle, which is a nifty
> feature.)
>
> Cheers,
>
> Steve
>
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>
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What's the inner scale on this photo for?

[Steve Lelievre]

Hi,

Today a website called Vermont Free Press published an appallingly 
confusing (to me) summary of types of sundials. If you can bear to look, 
it's at https://www.vermontpressbureau.com/types-of-sundials/


However, there was one thing about it that piqued my interest: the photo 
of an azimuth sundial ( 
https://www.vermontpressbureau.com/wp-content/uploads/2021/10/Azimuthal.jpg 
).


From what I can make out, there is a metal flap at the end of the 
alidade / sighting arm (the end at top in the photo). It must get turned 
up to make a shadow-caster.  I guess the arm has to be rotated so that 
the shadow falls along it, and time is then read from where the 
right-hand edge of the arm crosses the net of hour and declination 
lines. But then, wouldn't the screws seen in the upper plate block the 
arm from being turned to the required orientation?


Another bit I can't figure is the little circular scale just north of 
the centre of the dial, with the pointer. Perhaps just an Equation of 
Time scale? Or perhaps a cam connects it to the arm so that it can be 
used to set the arm's length? (The slot in the arm suggests it can be 
slid in and out to set the tip at the applicable declination circle, 
which is a nifty feature.)


Cheers,

Steve

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Re: Construction method of early North American pewter dials

[Steve Lelievre]

Hi everyone,

Many thanks to Maciej Lose for an off-list reply with these links which 
fully answer my questions: gnomon and dial cast were together using 
multipart molds for easy removal.


https://www.metmuseum.org/art/collection/search/8028

https://www.metmuseum.org/art/collection/search/8028


Also, thanks to Fred Sawyer for answer on the list:

https://www.google.com/books/edition/Goldsmith_Chandlee_Sundial_Maker_Setting/iKfIDAAAQBAJ?hl=en=1=goldsmith+chandlee=frontcover 
<https://www.google.com/books/edition/Goldsmith_Chandlee_Sundial_Maker_Setting/iKfIDAAAQBAJ?hl=en=1=goldsmith+chandlee=frontcover>

P.15 shows a photo of the brass mold used to make pewter dials.

Cheers,
Steve



On 2021-10-24 1:21 p.m., Steve Lelievre wrote:
My questions relate to the mass-produced cast pewter dials that were 
apparently commonplace in 18th and 19th century in North America. A 
1762 example is shown at 
https://digitalcollections.nypl.org/items/510d47d9-50fb-a3d9-e040-e00a18064a99#


Were these dials normally cast as a single piece, as opposed to, for 
example, the dial face and gnomon being cast separately and then 
soldered together? Are any molds known to have survived? If so, where 
held?


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Construction method of early North American pewter dials

[Steve Lelievre]

Hi,

My questions relate to the mass-produced cast pewter dials that were 
apparently commonplace in 18th and 19th century in North America. A 1762 
example is shown at 
https://digitalcollections.nypl.org/items/510d47d9-50fb-a3d9-e040-e00a18064a99#


Were these dials normally cast as a single piece, as opposed to, for 
example, the dial face and gnomon being cast separately and then 
soldered together? Are any molds known to have survived? If so, where held?


Sunny days,

Steve


///workers.exist.lookout

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Re: Does this type of dial have a name?

[Steve Lelievre]

Peter,

That's an good question, and you've already had a couple of informative 
replies.


My 2 cents worth is to say that I wish we had a clearer system of 
nomenclature. There were conversations a few years back but no 
consensus, and I don't think there's any benefit in reopening the topic. 
I will say though, that your question demonstrates the overlap between 
two aspects of a dial - the type of dial (the physical configuration) 
and the time system (type of hours kept) - even though our naming tends 
to be based one or the other aspect but not both.


I believe Ildephonse's dial was a Vertical Dial. The system of hours 
shown was Mean Time. Wouldn't it be nice if the name told us both bits 
of information?


Steve








On 2021-08-15 10:00 p.m., Peter Mayer wrote:


Hi,

A friend recently returned from Port Augusta and sent me photos of a 
dial in the Australian Arid Lands Botanic Garden (attached). The 
Garden describes it as a 'Projection Dial', but clearly that isn't a 
unique name for this form of sundial with EOT corrections for each 
hour. The earliest example I've seen described is the vertical dial by 
Père Ildephonse at the Convent Cimiez-Sur-Nice (the illustration is 
from Cousins' _Sundials_ which dates from c. 1876. Is this the 
earliest example of such a dial? And, again: does it have a unique name?


best wishes,

Peter

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Pewter casting

[Steve Lelievre]

Hello sundial friends,

I know that cast pewter sundials were used in the past ... perhaps 
someone on this list has used modern lead-free formulations of pewter to 
cast gnomons or other sundial parts.


I am seeking general advice and experiences, and I would be extra happy 
to hear from anyone who has tried doing it using 3D-printed moulds.



Sunny days,

Steve


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Re: true North

[Steve Lelievre]

Ed,

To find True North, many dialists use Hindu Circles (also known as 
Indian Circles). It's worth reading up on the method if you want to 
learn a bit of theory about the sun's daily path as it relates to 
sundials. There's a brief description of the method at bullet point 4 at 
https://www.mysundial.ca/tsp/true_north_south.html but for a full 
explanation you'll need to refer to sundialing books or websites.


If you prefer to use a magnetic compass, you can do so by adjusting for 
magnetic declination. There's a handy tool for figuring out your local 
magnetic declination at https://www.geomag.nrcan.gc.ca/calc/mdcal-en.php.


In practice, a simple and reliable method for finding North is to use 
software to tell you what the sun's azimuth is at a certain instance 
during the day, and to use the shadow of a perfectly vertical rod or a 
plumb line (if you are out of the wind) as a pointer. A convenient time 
to do this is when the sun is due south because that is when the shadow 
of the rod or line points due north (in the Northern hemisphere). At 
http://www.suncalc.org there is a suitable webpage (and also an Android 
app called SunCalc) for telling you the current solar position. Another 
option is my SDN (for Solar Data Now) offering, suitable for a phone's 
browser or a desktop browser. It is less sophisticated than SunCalc but 
should also do the job. The link is https://www.gnomoni.ca/sdn


The above methods are for finding North. If your  need is only to check 
that a sundial is correctly aligned, use the SunCalc or SDN to tell you 
the current solar time at your location, and turn your sundial to match.


Steve





On 2021-02-18 1:04 p.m., Ed wrote:
I know this is a basic question for most here but I am just trying to 
figure this out I have built a few prototypes out of cardboard.

I am lat long 30.730401 north
longitude 97 degrees 41.83 west
Thanks Ed

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Re: request

[Steve Lelievre]

André,

Maybe one of these?

New Method Of Setting Sundials – An Improvement / Rolf Wieland / The 
Compendium 21(1), March 2014, pp.12-14


Introduction: In The Compendium 20(4) from December 2013 we could read 
on page 4 the following intriguing method of setting a sundial described 
in the Time's Telescope for 1824 (Nov. 1824, p. 283): On a bright day, 
set a watch exactly with the dial at 9 o'clock in the morning, and at 3 
in the afternoon observe the difference between them, and correct the 
dial to half this difference. Proceed in the same manner till the watch 
and dial are found to agree perfectly. This is a surprising and easy 
method and in the beginning I could not believe it would work...



An Easy Method To Find Proper Alignment / Bill Gottesman / The 
Compendium 9(2), June 2002, pp.7-16


Does your sundial read properly all day long, or does its accuracy drift 
during the day? Would you like to have an easy method to determine how 
to adjust your dial’s position to accurately read solar, standard or 
daylight savings time? This article describes a new method for taking 
three time measurements from your dial, and then using that information 
to calculate how to tilt your dial to obtain accurate alignment with the 
North Pole and the time meridian of your choosing



Cheers,
Steve


On 2020-08-08 9:59 a.m., André Reekmqns wrote:


Looking for the 3 pages article published in BSS or NASS 10 years? 
about rectifying a misaligned pole-style horizontal or vertical sundial.


André Reekmans

Sundial Society of Flanders, Belgium.


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Re: Advice sought re:transparent sundial design

[Steve Lelievre]

Michael,

For sure.

I simply ignored the possibility of Babylonian Hours because I 
personally don't think they have much practical use (to the extent that 
any sundial has practical use these days). For a dial showing hours to 
sunset, on the other hand, I do see some hint of practical use. It will 
tell me if I have time to mow the lawn or finish painting the fence 
before it gets dark, and so on. As well, for observers of some 
religions, a sunset dial could be used to know approximately how much 
time is left until, for example, the Sabbath starts or until a daytime 
fast can be broken.


Steve





On 2020-04-22 5:52 a.m., Michael Ossipoff wrote:
Because the dial is a translucent-double one, with gnomons on both 
sides of the dial-plate, it would tell time all day, and so it could 
give Babylonian-hours in addition to co-Italian hours.


On a single dial, with everything on the same dial-face, it would 
avoid clutter to show Babylonian hours only in the morning, and 
co-Italian hours only in the evening. But, with the very wide hole in 
the wall, there's easily room for 3 dials, with one exclusively for 
Babylonian and co-Italian, and so it wouldn't be cluttered to show 
both for all day.


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Re: Seeking information about a topiary sundial at Ascott House, Buckinghamshire, UK

[Steve Lelievre]

Patrick, Patrick and Frans,

So, it's just a horizontal dial with the tip of the topiary tree acting 
as a nodus?


I see now that you're right, even if it's a little disappointing!

Thanks,
Steve



On 2019-10-03 8:15 a.m., Steve Lelievre wrote:


... Ascott House. ...
The gnomon has a fairly strange shape so I guess that either only the 
top part or only the bottom part is functional, but even then I can't 
figure out what it does. ...


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Seeking information about a topiary sundial at Ascott House, Buckinghamshire, UK

[Steve Lelievre]

From my daily Google digest message, I just learned of the existence of 
topiary sundials. A web search then led me to the example at Ascott 
House. There's a nice photo of it at 
http://www.siteandinsight.com/wp-content/uploads/2016/10/Ascott-3-of-14.jpg


The gnomon has a fairly strange shape so I guess that either only the 
top part or only the bottom part is functional, but even then I can't 
figure out what it does. Is this some kind of azimuthal dial - maybe 
even just using the crude approach of 15 degrees per hour?


Cheers,

Steve

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Re: Sundial designs against vandalism

[Steve Lelievre]

Assuming the question relates to the gnomon of a traditional Horizontal
Dial, then perhaps use a design with a very wide gnomon. That ought to make
it harder to bend it, and gives more contact area on the dial faces for
more screws.

Steve

On Thu, Sep 26, 2019 at 01:00, Dan-George Uza 
wrote:

> Hello,
>
> Horizontal sundials are often victims of vandalism. I am looking for ideas
> or designs of gnomons which are not that easy to break off i.e. how to
> attach them permanently to the base plate.  Can you help?
>
> Thanks,
>
> --
> Dan-George Uza
> ---
> https://lists.uni-koeln.de/mailman/listinfo/sundial
>
> --
Cell +1 778 837 5771
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Re: New book: Sundials of the Adler Planetarium, by Sara J. Schechner

[Steve Lelievre]

NASS members,

Please check the email sent earlier today (Aug 15) regarding special
arrangements for NASS members wishing to ordering this book.

Best,
Steve
NASS Secretary



On Thu, Aug 15, 2019 at 14:14, Pedro Raposo  wrote:

>
> I am pleased to announce the publication of *Time of Our Lives: Sundials
> of the Adler Planetarium*, by Sara J. Schechner. Please find below a
> description of the book.
>
> --
Cell +1 778 837 5771
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Fwd: Fwd: Re: Sunrise/sunset in old calendars/almanacs

[Steve Lelievre]

Dan,

Now I have finished my calculations.

The first table below shows the latitude that gives the minimum total 
error evaluated over the whole the year, where error is assessed as the 
square of the difference between true day length and day length given in 
your calendar (in other words, I'm using a Least Squares fitting 
method). There are three rows of results, for each possible definition 
of sunset. There are two columns of results, for the two ways that day 
length can be obtained from the calendar - sunset minus sunrise; stated 
day length.


The second table shows the same combinations of options. The latitude is 
again chosen for the smallest error, but for this table the result is 
assessed using the smallest individual error for any day of the year 
(that is, the minimum absolute value of 365 daily values).


I did my calculations using the "Solver" goal-seeking add-on for Excel. 
For the first table it used non-linear regression. For the second table 
it used an evolutionary algorithm.


I haven't looked at the reliability of the sunrise and sunset times 
(except to use the difference to get day length).


My overall conclusions: you're right - it's not possible to extract the 
latitude from the data (the result varies significantly depending on the 
evaluation method and assumptions used); as well, the calendar isn't 
very reliable (whichever way I did the calculation, I found that that 
day length errors of a least 1.2 hours occurred at some point in the 
year, compared to the true values [not considering twilight as day time]).


Steve



Best Latitude: By Minimizing the Sum of Squares of Daily Errors
Estimated Latitude 		Using Stated Sunset minus Stated Sunrise 	Using 
Stated Day Length

Sun sets when centre is on the true horizon  0.00   47.045  44.888
Sun sets as upper cusp dips below horizon   -0.26   46.958  44.794
Sun sets as upper cusp dips, with allowance for refraction 	-0.83 
46.708 	44.532








Best Latitude: By Making the Worst Error As Small As Possible
Estimated Latitude 		Using Stated Sunset minus Stated Sunrise 	Using 
Stated Day Length

Sun sets when centre is on the true horizon  0.00   45.320  47.043
Sun sets as upper cusp dips below horizon   -0.26   45.327  47.050
Sun sets as upper cusp dips, with allowance for refraction 	-0.83 
45.336 	46.468






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Re: Sunrise/sunset in old calendars/almanacs

[Steve Lelievre]

Hi again,

Yes, with the extra months now available, I get a very different result. 
Using only April was a lucky hit, I guess. Using April to December with 
the same method as before, I get:


Altitude of sun at sunset : latitude
 0.00 : 47.05
-0.26 : 46.96
-0.83 : 46.71

Dan, the December day length and night length do not add to 24 hours. Is 
that really so in the source document?


Cheers,
Steve




On 2019-08-09 1:25 p.m., Dan-George Uza wrote:

Hello again,

Here is the complete data with the exception of the first three months 
which have been lost:


April 1793 - sunrise: 5:20 and sunset: 07:14
 - day length - 13 hours and 20 minutes, night - 10 
hours and 40 minutes


May 1793 - sunrise: 4:33 and sunset: 07:47
 - day length - 14 hours and 54 minutes, night - 9 
hours and 6 minutes


June 1793 - sunrise: 4:05 and sunset: 07:47
 - day length - 14 hours and 53 minutes, night - 9 
hours and 7 minutes


July 1793 - sunrise: 4:12 and sunset: 07:44
 - day length - 15 hours and 36 minutes, night - 8 
hours and 24 minutes


August 1793 - sunrise: 4:51 and sunset: 06:39
 - day length - 14 hours and 18 minutes, night - 9 
hours and 42 minutes


September 1793 - sunrise: 5:41 and sunset: 05:29
 - day length - 12 hours and 38 minutes, night -11 
hours and 22 minutes


October 1793 - sunrise: 6:24 and sunset: 05:20
 - day length - 10 hours and 52 minutes, night - 13 
hours and 8 minutes


November 1793 - sunrise: 7:24 and sunset: 04:21
 - day length - 9 hours and 12 minutes, night - 14 
hours and 38 minutes


December 1793 - sunrise: 7:54 pm and sunset: 4:05 pm
 - day length - 8 hours and 12 minutes, night - 8 
hours and 48 minutes



Dan Uza

On Fri, Aug 9, 2019 at 10:50 PM Dan-George Uza 
mailto:cerculdest...@gmail.com>> wrote:


Dear Steve,

I will share the data for the whole year once I get it (I only
have April). Your preliminary results sound too good to be true.
I did a simulation using TimeAndDate.com for three completely
different locations on the European continent: Constanta
(Romania), Gorlitz (Germany) and London (UK). I chose these
because of their proximity to the time zone meridians, this way
the old solar time is more easily found (I just exclude 1h
daylight saving time).

The stated duration of the day of 13h20min for April is recorded
in those localities on April 13, April 7, respectively April 7
(all gregorian, the last two cities have approximately the same
latitude).
Sunrise on these respective dates (in solar time): 5:24 in
Constanta, 5:23 in Gorlitz, 5:23 in London.
Sunset (in solar time): 18:47 at Constanta, 18:42 at Gorlitz,
18:43 at London.

In the calendar we've got sunrise at 5:20, which is a good enough
fit for all the above examples.
On the other hand, sunset is at 7:14 (p.m.) and this time doesn't
fit any of the examples above.
If we consider it to be the civil twilight, we have 19:16 for
Constanta, 19:16 for Gorlitz, respectively 19:17 for London (old
hours). These correspond quite well with the sunset given by the
calendar.

Dan Uza

On Fri, Aug 9, 2019 at 10:15 PM Steve Lelievre
mailto:steve.lelievre.can...@gmail.com>> wrote:

Dan,

Using only your April data, and assuming:

1. day length is the difference of the sunset and sunrise (as
opposed to the daylength stated),
2. sunrise and sunset are when the center of the sun is on the
horizon
3. my modern source of solar declination data is "good enough"
4. your table of values is for the Julian calendar, which for
the year in question is offset from the Gregorian calendar by
11 days,

then, by varying latitude to minimize the Sum of Squares of
the differences between true day lengths and the
representative day length stated  I get a latitude of
44.413N, which would correspond to Bucarest.

If I could use your table of data for the full year, the
result would of course be different - better, I would hope,
but possibly not!

As yet, I have no idea why the stated day length is not the
same as the difference of the sunrise and sunset.

Steve


On 2019-08-09 1:06 a.m., Dan-George Uza wrote:

Hello all,

I have seen an old calendar from 1793 which lists for every
month sunrise and sunset times as well as day and night
duration. For example, taking the month of April: sunrise at
5 h 20 m, sunset at 7 h 14 m; day length 13 h 20 min, night
length 10 h 40 m.

Somebody asked me if it would be possible to establish the
approximate geographical area for these predictions.

I'm pretty sure it's not possible. Back then they used t

Re: Sunrise/sunset in old calendars/almanacs

[Steve Lelievre]

Dan,

Using only your April data, and assuming:

1. day length is the difference of the sunset and sunrise (as opposed to 
the daylength stated),

2. sunrise and sunset are when the center of the sun is on the horizon
3. my modern source of solar declination data is "good enough"
4. your table of values is for the Julian calendar, which for the year 
in question is offset from the Gregorian calendar by 11 days,


then, by varying latitude to minimize the Sum of Squares of the 
differences between true day lengths and the representative day length 
stated  I get a latitude of 44.413N, which would correspond to 
Bucarest.


If I could use your table of data for the full year, the result would of 
course be different - better, I would hope, but possibly not!


As yet, I have no idea why the stated day length is not the same as the 
difference of the sunrise and sunset.


Steve


On 2019-08-09 1:06 a.m., Dan-George Uza wrote:

Hello all,

I have seen an old calendar from 1793 which lists for every month 
sunrise and sunset times as well as day and night duration. For 
example, taking the month of April: sunrise at 5 h 20 m, sunset at 7 h 
14 m; day length 13 h 20 min, night length 10 h 40 m.


Somebody asked me if it would be possible to establish the approximate 
geographical area for these predictions.


I'm pretty sure it's not possible. Back then they used true solar time 
(or perhaps mean solar time?) so I guess these hours would have been 
valid for a whole parallel of latitude, with variations once you go 
north or south.


Nevertheless, I made a simulation and realized that I cannot get close 
to these numbers. I don't know why. Perhaps because back then sunrise 
and sunset was not counted by solar limb, but by geometric center of 
the Sun? How did they do it?


Regards,

--
Dan-George Uza

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Re: AW: What accuracy to aim for with a carefully made sundial?

[Steve Lelievre]

ndial since
years) that the
lines correctly follow the shadow on time.

4) I am on to build a sundial with a second reading of high
noon - and did
do the concerning presentations (theory, fulfilled and planned
implementation steps) at sundial conferences in Austria.

Good luck!
Kurt

-Ursprüngliche Nachricht-
Von: sundial [mailto:sundial-boun...@uni-koeln.de
<mailto:sundial-boun...@uni-koeln.de>] Im Auftrag von Steve
Lelievre
Gesendet: Dienstag, 30. Juli 2019 19:38
An: Sundial List mailto:sundial@uni-koeln.de>>
Betreff: What accuracy to aim for with a carefully made sundial?

Hello everyone,

I'm planning to make a small vertical west dial, about 1m for
the width of
the dial face, at my latitude of 49N. It will not use a nodus.

The angular width of the sun makes it hard to get a really
accurate time
reading, but there will also be small errors from
mis-positioning of the
dial plate when installing (declination and inclination),
imprecise
positioning of the gnomon or the hour lines, and perhaps other
causes too.

First, questions directed at those of you who have practical
experience of
creating vertical sundials: If I'm careful and have a
well-machined gnomon,
what level of accuracy might be achievable in practice? I assume
+/- 5 minutes throughout the day and year is fairly easy to
achieve, but
what about +/- 2 minutes, or even +/- 1 minute? How well did
you do? How did
you measure your wall's declination?

Second, have there been any studies of how well dial users
compensate for a
penumbra - by which I mean gathering data from volunteers,
studying the
spread of errors in time readings taken from a dial versus a
reference time
source? (without employing a shadow sharpener)

Thanks,

Steve



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What accuracy to aim for with a carefully made sundial?

[Steve Lelievre]

Hello everyone,

I'm planning to make a small vertical west dial, about 1m for the width 
of the dial face, at my latitude of 49N. It will not use a nodus.


The angular width of the sun makes it hard to get a really accurate time 
reading, but there will also be small errors from mis-positioning of the 
dial plate when installing (declination and inclination), imprecise 
positioning of the gnomon or the hour lines, and perhaps other causes too.


First, questions directed at those of you who have practical experience 
of creating vertical sundials: If I'm careful and have a well-machined 
gnomon, what level of accuracy might be achievable in practice? I assume 
+/- 5 minutes throughout the day and year is fairly easy to achieve, but 
what about +/- 2 minutes, or even +/- 1 minute? How well did you do? How 
did you measure your wall's declination?


Second, have there been any studies of how well dial users compensate 
for a penumbra - by which I mean gathering data from volunteers, 
studying the spread of errors in time readings taken from a dial versus 
a reference time source? (without employing a shadow sharpener)


Thanks,

Steve



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Re: Early movie clip of a solar eclipse

[Steve Lelievre]

Oops, sorry.

The name is question is "Nevil Maskelyne" (cut and paste a typo = lots 
of typos!)


Steve

On 2019-06-02 8:05 p.m., Steve Lelievre wrote:

Hi everyone,

In case you missed this news item from the last few days: British Film 
Institute (BFI) have just released a digital version of film footage 
of a 1900 solar eclipse - the earliest known successful recording.


https://youtu.be/q4jfPfMKBgU

The footage was shot by Neville Makelyne, a British stage magician 
turned cameraman (not the Astronomer Royal of the same name). BFI 
report that it was Makelyne's second attempt at recording a solar 
eclipse. His first try was in India in 1898, but the undeveloped film 
was stolen as he travelled home to England.


Cheers,

Steve

P.S. Apparently Makelyne is also known for disrupting Guglielmo 
Marconi's early public demonstrations of commercial radio telegraphy. 
Makelyne was paid by a consortium of undersea telegraph cable owners 
to try to undermine Marconi's fledgling business. He would set up his 
own radio transmitter in buildings near to where Marconi's 
demonstrations were taking place in London, and thus swamp out 
Marconi's faint signals from North America.





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Early movie clip of a solar eclipse

[Steve Lelievre]

Hi everyone,

In case you missed this news item from the last few days: British Film 
Institute (BFI) have just released a digital version of film footage of 
a 1900 solar eclipse - the earliest known successful recording.


https://youtu.be/q4jfPfMKBgU

The footage was shot by Neville Makelyne, a British stage magician 
turned cameraman (not the Astronomer Royal of the same name). BFI report 
that it was Makelyne's second attempt at recording a solar eclipse. His 
first try was in India in 1898, but the undeveloped film was stolen as 
he travelled home to England.


Cheers,

Steve

P.S. Apparently Makelyne is also known for disrupting Guglielmo 
Marconi's early public demonstrations of commercial radio telegraphy. 
Makelyne was paid by a consortium of undersea telegraph cable owners to 
try to undermine Marconi's fledgling business. He would set up his own 
radio transmitter in buildings near to where Marconi's demonstrations 
were taking place in London, and thus swamp out Marconi's faint signals 
from North America.



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Re: Strange analemmatic sundial - how does it work?

[Steve Lelievre]

Thank you to Joel, Fabio, and Bill.

Before I sent off my inquiry last night, I had got as far as deciding 
the dial must be some kind of Foster-Lambert similar to the Herstmonceux 
dial that Fabio mentioned, but I was still confused. I'm relieve to 
learn that it's not related to an analemmatic dial at all, and Wikipedia 
is simply wrong!


Steve


On 2019-05-31 5:14 a.m., Bill Gottesman wrote:

Hello Steve, I'll take a guess at this.
I think the dial is really a heliochronometer with an analemma, not an 
analemmatic dial.  I think the screws up top held a focusing lens or a 
pinhole aperture that projected a beam on to an analemma on to the 
lower plate.  The analemma is not visible in that picture.  The dial 
is turned to make the beam align, so the hours go counter-clockwise, 
and the time is read across from stationary indicator at the very top 
of the dial, hidden from view in this photo.
Similar to the upper left dial seen at 
https://equation-of-time.info/sundials-with-shaped-alidades . -Bill


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Strange analemmatic sundial - how does it work?

[Steve Lelievre]

Hello everyone,

The English language Wikipedia page on analemmatic sundials has a photo 
of a strange example at the National Polytechnic Museum, Sofia. See 
https://en.wikipedia.org/wiki/Analemmatic_sundial and scroll down to the 
last photo.


It's completely unlike any other analemmatic dial that I know of, so I'm 
struggling to understand it. Which part is the gnomon? Which part 
moves?  Why do the hours run counterclockwise (Sofia is northern 
hemisphere so presumably it was made for use there)?  Why is there a 
brace apparently welded to the dial face in front of the XII position? 
What angle is the dial face at?


So many questions!

In short, how does it work ... can anyone enlighten me?

Thanks,

Steve




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Re: Historic sundials

[Steve Lelievre]

Dan,

For your question about sundials to discuss with school students, I 
would have to adjust my selection depending on the age of the students, 
but as a general starting point I would probably consider:


1. A merket, the Ancient Egyptian instrument - because although not 
everyone accepts them as sundials, they are contenders for being the 
oldest type of dial there is.


2. A shepherd's dial - because they are a really practical and reliable 
form of early portable dial. I also find that people seem to understand 
them quite easily.


3. A scaphe marked with seasonal declination lines - because they are 
another ancient form of dial and also provide a way to introduce the 
idea of the celestial sphere, and the celestial sphere projected onto a 
dial's surface, as well as demonstrating the path of the sun through the 
year.


4. A Foster-Lambert - because they are amenable to correction for 
Equation of Time and for time zone, and so provide a bridge to the age 
of clocks.


5. A horizontal - because I don't think I could manage to discuss 
sundials with school students without reference to such a well-known 
type: probably the type are most likely to encounter.


If I didn't have to stop at 5 examples, and if the students seemed 
particularly interested, I would perhaps show a few extras in order to 
further demonstrate the variety that exists:


6. A CD-based diffraction dial - for the fun factor.

7. A refraction dial - for the fun factor.

8. An armillary sphere - yet again to show another form, but also for 
the reasons given for (3).



Cheers,

Steve





On 2019-03-20 9:39 a.m., Dan-George Uza wrote:
If you were to make a presentation addressed mainly to schoolchildren 
or early college about some important historic sundials, which ones 
would you choose and why?


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Re: Equinox, Full Moon and Easter

[Steve Lelievre]

Roger, the Easter calculation uses March 21 as the equinox irrespective of
the astronomy.

Steve

On Tue, Mar 19, 2019 at 21:00, Roger  wrote:

> I always thought Easter Sunday was on the first Sunday after the first
> full moon after the spring equinox. This year at my location, time zone
> PDST, the equinox is at 2:59 pm Wed 20 March 2019. The full moon is about 4
> hours later at 6:43 pm. Why is this Sunday not Easter and Friday not Good
> Friday. What about the Passover. It is also a month later. I know setting
> the date of Easter was the problem that inspired astronomy but this year
> the scientific data and the religious credo do not seem to agree.
>
>
>
> Where have I been mislead? (other than finding silly girls posing as
> sundials)
>
>
>
> Roger Bailey
>
> Walking Shadow Designs
>
> N 48.669°, W 123.403°
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>
> --
Cell +1 778 837 5771
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Re: dischrony

[Steve Lelievre]

In my writings, I have been using the term Time Zone Offset (really, it 
should be Time Zone Meridian Offset but that would be too long).


I'm happy enough to change to some other term that is generally agreed, 
but I think the adopted term should provide an explicit indication of 
its purpose. In short, I think having 'Time Zone' in it is helpful - 
especially for newer dialists who are still developing their 
understanding of the discipline.


Steve


On 2019-03-12 9:01 a.m., Maes, F.W. wrote:
In The Netherlands we use "lengtecorrectie", abbreviated LC, which 
would translate to "longitude correction" in English.

Some (international) standardization of terminology would be nice!



On Tue, Mar 12, 2019 at 2:06 PM Michael Ossipoff 
mailto:email9648...@gmail.com>> wrote:


I usually say "Longitude-Correction".  Of course, for sundials,
it's always expressed in minutes.

But I like "Local Constant", because it's shorter.

What's wrong with "Local Constant"?   It /is/ a constant, for a
given locale.


On Tue, Mar 12, 2019 at 6:55 AM fabio.sav...@nonvedolora.it
 mailto:fabio.sav...@nonvedolora.it>> wrote:

In Italy some sundials show the written 'costante locale',
that can be
translated as 'local constant'.



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Re: Gnomon Gap Puzzle

[Steve Lelievre]

Frank,

May I have a second try at answering your quiz?

I'm still not doing it for a nickel, though.

My new suggestion would be much the same set-up as for my first 
suggestion, but this time I feel sure the dial face can be entirely 
within the noon gap area (that is, assuming the noon gap is defined as 
the area on the poleward side of the gnomon, and we're talking about a 
standard horizontal dial but with a very wide gnomon...


This time, I suggest that the "underside" of the gnomon should be a 
plane mirror. The upper side of the gnomon is not involved, so can be 
decorated as you like.


The left and right edges of the rectangular underside of the gnomon act 
as styles for an underslung dial that services azimuths -90 to 90, and 
also act as styles for a reflecting dial that services the remaining 
azimuths. All  the hour lines are in the area between the styles and are 
on the polar side of the gnomon. Some lines serve double duty. At least, 
I think so - I can't get it entirely clear in my head but as I visualize 
them, the same lines are applicable to both the reflected and underslung 
dials.


When the sun is on the polar side of the dial, it is read using the edge 
of the bright reflected area. When it's on the equator side, the dial is 
read using the edge of the shadow.


I've posted a crude representation of what I mean at 
http://www.gnomoni.ca/temp/quiz.png (northern hemisphere)


Steve








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Re: Gnomon Gap Puzzle

[Steve Lelievre]

Hello again, Frank,

A quick postscript to my first answer ... I can also get my 4 sub-dials 
by using parallelograms arranged in NS planes at the sides of the dial 
face, and sitting on the horizontal dial surface. The skew of the 
parallelograms would be such that they provide polar styles, so that 
each provides one overshot and one undershot style. This arrangement is 
using two gnomons though - like the Troschel dial - so is really two 
separate dials drawn with overlapping dial faces, hence it doesn't 
conform to the "all in the noon gap" requirement.


Steve



On 2019-01-01 7:41 a.m., Frank King wrote:

Steve: ...at first reading, you have a good
scheme which again shares elements of the
design I came up with!


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Re: Gnomon Gap Puzzle

[Steve Lelievre]

For Q1, my solution would be a bit like the set up already suggested by 
Maciej Lose from Hans Troschel. Instead of having two wires in a 
diptych, I would use a rectangular sheet of material. It would be set up 
with one pair of opposite edges on an East-West line, and the other pair 
parallel to the polar axis. The east and west edges then each act as a 
style for an undershot and an overshot sub-dial, giving me four 
sub-dials in total, all horizontals. Two are on the north side of the 
gnomon and 2 are south of it. Assuming northern hemisphere then:


The eastern style overshot  works for solar azimuth <= -90
The eastern style undershot works for solar azimuth -90 to 0
The western style undershot works for solar azimuth 0 to 90
The western style overshot works for solar azimuth >= 90

With the right size and aspect ratio for the rectangle then the sub-dial 
faces need not overlap, and only one face sees the sun at any instant, 
so there's no confusion about which face to use...does this solution 
count as being entirely within the noon gap, though?


For Q2, of course I say yes.

For Q3: I have absolutely no idea what Frank's space is, but I think my 
solution would fit well around a ground-mounted solar panel array - 
they're arranged East-West and poleward, aren't they?



Steve



On 2019-01-01 12:50 a.m., Frank King wrote:

Dear All,

Here is a little Dialling Puzzle to start
the New Year...

We are all familiar with the term 'Noon Gap'.
On a simple horizontal sundial with a plate
gnomon, this is the gap on the dial plate
between the two vertical faces of the gnomon.

On the dial plate, there are two lines for
12 o'clock with the noon gap between.  Often
this gap is left blank.  Sometimes there is
a date or, perhaps, the maker's name.

During the year just ended, I was asked to
design a dial which had to fit in a rather
unusual space.  After a little thought, I
decided on a solution.  In this...

  THE ENTIRE DIAL FITS INSIDE THE GNOMON GAP

Question 1: What does the design look like?

Question 2: Can this possibly look good?

Question 3: What is the 'unusual space'?

A Happy New Year to you all.

Frank King
Cambridge, U.K.

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Re: Orologi Solari n. 17

[Steve Lelievre]

Hello, all,

It is pleasing for me to see that the latest  Orologi Solari includes an 
article by Alessandro Gunella, describing my design for an Italian Hours 
Foster-Lambert dial.


However, I am slightly embarrassed to have to report that the website 
link provided by Mr. Gunella no longer works, as of earlier today.


Due to an unfortunate coincidence, the announcement of the new Orologi 
Solari arrived today, but today is also the day that the website ceased 
to exist. My plan had been to keep this website for a few more weeks and 
to announce the replacement when ready, but I misunderstood the contract 
and the supplier has just closed the old site. The fee to reinstate it 
is not justified.


Instead, I have placed a copy of the relevant page on a new site, at 
http://www.gnomoni.ca


Note, however, that I do not plan to reinstate all of my older sundial 
pages. Anyone looking for my other programs, or bits and pieces from the 
former va7lel.ca website, should contact me off-list.


With apologies for the inconvenience caused.

Steve Lelievre




On 2018-12-18 10:52 a.m., Gian Casalegno wrote:
12. "A horizontal Italic sundial by Foster – Lambert" by  Gunella 
Alessandro
In issue 24 number 2 of the NASS magazine "The Compendium" an 
interesting sundial proposed by Steve Lelievre, a Canadian gnomonist 
from Vancouver, showed off on the cover. This is an interactive 
horizontal Italic sundial of the Foster Lambert type. In this article 
an analysis of the author, using the usual graphical method, is exposed.




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Re: Bird shapes in gnomons

[Steve Lelievre]

On 2018-11-01 7:49 a.m., Schechner, Sara wrote:
I would not speculate that there was any mix or match; real evidence 
is needed.


Yes, I agree that evidence is needed.

I have seen the same gnomon casting used for different dial faces, and 
the same dial face with different gnomons. I supposed it could be from 
allowing customers to mix-and-match (or even the manufacturer treating 
parts as swappable), but on reflection I realize it is equally as likely 
to happening in the second-hand market as vendors discard broken or 
corroded parts and reassemble 'complete' dials from what's left.


Steve

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Re: Bird shapes in gnomons

[Steve Lelievre]

Hi Sara and John,

Thanks for your replies. It's interesting to be able to trace the bird 
motif to Butterfield's time. It just leaves me wondering why he chose to 
use a bird. Absent any other explanation, I'll assume it was whimsy.


Sara, because the URL you mentioned is a link to your CHSI website, 
clicking through reminded me of my visit during the NASS conference a 
few years back. I don't specifically remember the Butterfield dials in 
your collection, but I think that's maybe because I was so mesmerized by 
all the amazing, exquisite ivory diptychs that everything else pales in 
my memory. The photos of the Butterfields look pretty good too, though.


John, your comment that English dials tending to use fish or dolphins as 
supporters got me wondering if the use of birds is more of a North 
American thing, so I did a bit of Googling about that.


There's a bit of a story

It seems that mass production of cast iron and later cast bronze 
horizontal sundials in North America started in the late 19th or early 
20th C. Over the subsequent century, there seem to have been at least 
two companies that did well and that had gnomon designs featuring birds. 
I think this probably explains, in part, why I have encountered so many 
dials with this attribute.


One company, the W.J. Loth Stove company of Waynesboro, Virginia, was 
set up in 1890. They started out making stoves and cast kitchenware, and 
apparently were the original owners of the Hotpoint brand of home 
appliances. By the late 1930s they were using the brand name Virginia 
Metalcrafters, which later became the company name, for an assortment of 
decorative home goods including sundials. They ceased trading in 2006. 
The other company  is Rome Industries of Peoria, Illinois, founded in 
1964 and still operating. Their range of sundials are generally 
remarkably similar to the Virginia Metalcrafters line. In fact, one 
could be forgiven for thinking that some models are copies of the other 
company's products. Compare Virginia Metalcrafters'  
https://tinyurl.com/yd6qsqk4 and Rome's  https://tinyurl.com/y75dorrk . 
If they aren't copies, could it be that both are modeled after the same 
earlier design - I wonder.


Both companies seem to have had a small choice of dial faces, mottos 
(basically the same wordings available from both companies), and gnomons 
(including the bird device) so my guess is that customers could mix and 
match. Both have winged hourglasses as dial furniture (referring to 
"time flies"). At least Virginia Metalcrafters had wedges at the bottom 
of the gnomon, which I guess allowed for milling to the appropriate 
angle - in which case I imagine that each of the the stock dial faces 
would have needed a few latitude variants too. By around 1950 Virginia 
Metalcrafters had some kind of arrangement with the US National Parks 
Service to make reproduction dials for US National Historic Sites. After 
closing down, their factory was designated as a Historic District.


Long story short, because of these two companies, there are quite a lot 
of sundials dotted around North America, including some at much-visited 
National Historic Sites, with bird gnomons. There are even several on 
eBay at the present time.


None of this explains why they chose birds, though.

But one more thing: after looking at a few photos today, I got to 
wondering if the bird isn't /always/ a bird. For example the one at 
https://tinyurl.com/ychwhnz4 looks more like a phoenix or griffin to me. 
More googling, and I learned that the phoenix has sometimes been 
associated with or used to represent the sun, also time.


Cheers,

Steve
































On 2018-10-30 12:09 p.m., Schechner, Sara wrote:

Hi Steve,
You may know about the fabulously popular, fashionable Paris accessory from 
circa 1675 to the end of the 18th century:  The Butterfield-type dial.  The 
pocket dial had a gnomon with an adjustable angle for use at different 
latitudes.  A sweet little bird's beak was the index on the latitude scale.  
See here for examples: http://waywiser.rc.fas.harvard.edu/search/butterfield

Invented by Michael Butterfield, they were made by many different makers in 
Paris.  They were so desirable that counterfeits were made signed Butterfield.

Sara


and

On 2018-10-30 11:34 a.m., John Davis wrote:

Hi Steve,

The obvious early source for bird gnomons is the Butterfield style of 
portable dials.


In England, the most common animal supporter is a dolphin or stylised 
fish.


Regards,

John
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Bird shapes in gnomons

[Steve Lelievre]

Hello,

Gnomons on horizontal dials are mostly either undecorated triangles, or 
have simple polygonal or sigmoidal fretwork. However, recently I 
realized that the next most common form I encounter is a gnomon carved 
with the shape or silhouette of a bird. For example:


http://sundials.org/images/NASS_Registry/Dial_334/334_md_towson_hampton_2a.jpg

http://sundials.org/images/NASS_Registry/Dial_325/325_md_baltimore_clyburn_1.jpg 
(using a small stick to replace the missing filament that formed the style)


http://sundials.org/images/NASS_Registry/Dial_920/920_bc_vancouver_knox_church-2a.jpg

Is it coincidence that I encounter these designs relatively often? Or, 
is there some tradition of using bird motifs on sundials? If so, how did 
it originate and what do they symbolize?


Steve




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Re: Accuracy of wristwatch as compass

[Steve Lelievre]

Michael,



On 2018-10-24 8:25 p.m., Michael Ossipoff wrote:
A Shephard’s Dial wouldn’t help as a sun-compass. It just gives time 
if you know the date, or date if you know the time.


By writing "a Shepard's Dial marked out as a solar compass" I meant that 
one for which the lines drawn on the cylinder are the azimuth 
corresponding to altitude instead of the usual option of the hour 
corresponding to altitude.  So, yes, a sun compass.



Sure, an Altitude-Dial is at its least accurate near noon, but this AW 
method, and the TA that it’s based on, are different. The error is 0 
at noon, if you’re using the right EoT and longitude. The altitude 
(ideally along with the declination) adjusts h, to get the azimuth 
from south.


.

The error is max sometime during mid-afternoon because, because it’s 0 
at noon, and because, when the sun is low near sunset,h is multiplied 
by a only a factor, closer to 1, because cos dec * sec Alt is closer 
to 1 then.


.

AW’s error comes from the fact that it substitutes h and Azimuth for 
their sines. When the factor by which sin h is multiplied is closer to 
1, the error from that substitution is smaller.


.

So AW has its greatest error around mid-afternoon, between noon when 
it’s 0, and near sunset when it’s error is low due to that 
multiplicative factor being closer to 1.


OK, I see what you're saying now. I was coming at it just by imagining 
how hard it must be to get an accurate altitude measurement - perhaps a 
few degrees out. My thinking was that around noon the azimuth changes a 
lot from a small change in altitude so any measurement error would be 
multiplied considerably, whereas later or earlier in the day the same 
small change in altitude would correspond to a smaller change of azimuth.


Cheers,

Steve



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Re: Accuracy of wristwatch as compass

[Steve Lelievre]

Hello, Michael,

On 2018-10-24 8:42 a.m., Michael Ossipoff wrote:

The Shadow-Tip method [has] accuracy is greater at lower latitudes.


That's putting it mildly, I think. The method would be OK everywhere 
around midday or near an equinox but I suspect it's really, really bad 
if used early or late on a midsummer day at higher latitudes. I'm from 
55N, and for that latitude I reckon it could reach as much as 45 degrees 
off outside of the midday period in summer.



I've nearly always gotten very good results with [the Altitude
Watch method], though there are combinations of time-of-year
and time-of-day when it loses accuracy. Midsummer and roughly
mid afternoon or morning.

Maybe I've misunderstood, the method but I don't understand why 
mid-afternoon and mid-morning are the bad times of day. Why is that? I 
would expect it to be around noon, when the sun's azimuth can change 
significantly for relatively little change in altitude.


Anyway, your method reminded me of another altitude method -  a 
Shepard's Dial marked out as a solar compass.  I once made one and it 
worked pretty well, with a bit of degradation around noon. A Mr. 
Singleton was the first person I know of to publish the idea.


Steve
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Re: Hour label question

[Steve Lelievre]

Thank you to everyone who has replied to my question about the labeling 
of noon.


Summary of responses received:

Due to space constraints, a label of XII is sometimes replaced by 
something narrower. I'll hazard a guess that the use of Roman I, in the 
example I saw at Knox United Church, Vancouver, is pretty unusual. Using 
it to mark noon on a solar hours dial seems to be a potential source of 
confusion (well, it confused me).


I like the idea of a Cross Pattee as mentioned by Patrick Power, or the 
N mentioned by Don Snyder. I think I'll use one or the other of these 
symbols for any dials I make in the future, although the latter wouldn't 
work for all languages.


Roger Bailey mentioned that digit zero is often used for the same 
purpose. That is another option previously unnoticed by me but, in a 
remarkable coincidence, it was in a photo sent to me earlier that day by 
Sasch Stephens, and then the next day I encountered an identical dial in 
Kelowna BC.


According to Wikipedia, these dials' depiction of a winged hourglass 
represents "tempus fugit" ("time flies"). There seem to be plenty of 
other dials, at least in North America, that use the winged hourglass, 
and also 0 for noon for that matter. See, for example, the dials 
illustrating Don Synder's paper about the dial at Jefferson Barracks 
near St. Louis MO.



Photo of Kelowna dial: https://tinyurl.com/y7msj68h

Note about winged hourglass: https://en.wikipedia.org/wiki/Hourglass

Don Snyder's paper about Jefferson Barracks: 
http://dls-website.com/documents/JeffersonBarracksSundial.pdf



Cheers,
Steve


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Re: Please help me with a calculation

[Steve Lelievre]

Michael,

Thanks for your replies.


On 2018-09-27 8:50 PM, Michael Ossipoff wrote:
I'll fill in those topics*, describing the derivation in more detail,  
in postings here, if you'd like [ ... snipped ...]


*for the problem of finding how azimuth-misaligned the dial must be, 
to have a given wrong time-reading, at a given local true solar time 
and solar declination.


I'll take a rain check on that, if I may. I have received explanations 
(off list) from Brian Albinson and Hank De Wit  which I want to finish 
studying before asking for more help.


By the way, I should add that of course all that's necessary is that 
the dial be azimuth-rotated so that it tells the time that it should 
tell, and so it isn't necessary to solve the problem that we're 
talking about in order to azimuth-align the dial.


Yes, of course - but I'm not going to be correcting the dial myself. I 
will tell the parks department what I think is wrong and I want to 
provide nice simple guidance to help them decide if they want to do 
anything about it. Saying something like "Twist the dial about the 
vertical, so that rod in the middle is on a north-south line with the 
upper end pointing towards the north pole. The line has to be true 
north-south not magnetic north-south. You'll need to move it by 7.5 
degrees" is more likely to get action than a procedure that requires 
them to obtain and work with local solar time (extra hard for a dial 
that only shows hours and half hours, and for a job that likely wouldn't 
be carried out at a specific date and time).


Steve


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Re: Please help me with a calculation

[Steve Lelievre]

Hi again,

It seems that the equation that I typed out in my message below does not 
show correctly on all email software, so here it is again but written 
using ordinary letters:


dH = a2 ( cos(lat) x cos(H) x tan(dec) – sin(lat) )

where
dH : delta H, error in hour angle
H:  hour angle (0 at noon)
a2: azimuth error (assumed small)
dec: solar declination

I visited the dial in question again yesterday at solar noon. I 
estimated the time error as equivalent to  5.28° of hour angle. For the 
latitude of 49.24°N, the equation yields -7.83° for a2, the azimuth error.


That's reassuringly close to the previous day's estimate of -7.31°, and 
consistent with a guess of -7 ± 1° that I obtained by sighting a 
landmark across the arms of the dial and then measuring its bearing on 
Google Maps.


Steve






On 2018-09-26 10:05 AM, Steve Lelievre wrote:


Hello again,

I thank Hank de Wit, Brian Albinson and Jan Safar for replies (off 
list) offering suggestions for how to resolve my enquiry. Hank managed 
to find a journal article ( https://tinyurl.com/y7rmknpf ) that 
discusses sources of error in equatorial dials. The reference is: 
Garstang, R. H. (1997). /The errors of an equatorial sundial/, in The 
Observatory, v. 117, p. 344-351.


Unfortunately the article doesn't provide derivations, simply saying 
"a simple calculation by spherical geometry shows...", but, case (ii) 
of the analysis addresses the situation I encountered, stating


δH=a2(cos(ϕ)cos(H)tan(δ)-sin(ϕ))δH = {a}_{2}(\cos\left({ϕ}\right) 
\cos\left({H}\right) \tan\left({δ}\right) - \sin\left({ϕ}\right))


where δH is the time error, a2{a}_{2} is the angle by which the dial 
is twisted, ϕϕ is latitude, HH is hour angle, and δδ is solar declination.


Putting in the known values, gives a2{a}_{2} = 7° 18'. Using my cell 
phone compass I had guessed it as 10° or a little under.


Cheers,
Steve


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Re: Please help me with a calculation

[Steve Lelievre]

Hello again,

I thank Hank de Wit, Brian Albinson and Jan Safar for replies (off list) 
offering suggestions for how to resolve my enquiry. Hank managed to find 
a journal article ( https://tinyurl.com/y7rmknpf ) that discusses 
sources of error in equatorial dials. The reference is: Garstang, R. H. 
(1997). /The errors of an equatorial sundial/, in The Observatory, v. 
117, p. 344-351.


Unfortunately the article doesn't provide derivations, simply saying "a 
simple calculation by spherical geometry shows...", but, case (ii) of 
the analysis addresses the situation I encountered, stating


δH=a2(cos(ϕ)cos(H)tan(δ)-sin(ϕ))δH = {a}_{2}(\cos\left({ϕ}\right) 
\cos\left({H}\right) \tan\left({δ}\right) - \sin\left({ϕ}\right))


where δH is the time error, a2{a}_{2} is the angle by which the dial is 
twisted, ϕϕ is latitude, HH is hour angle, and δδ is solar declination.


Putting in the known values, gives a2{a}_{2} =  7° 18'. Using my cell 
phone compass I had guessed it as 10° or a little under.


Cheers,
Steve





Hi folks,

The equatorial sundial at Vandusen Gardens in Vancouver BC is a lovely piece 
but I think it is set up wrong - I suspect the dial's axis  is not aligned to 
the meridian. This suspicion is based on the measurements described below, but 
also because when I viewed the dial today I concluded it is not aligned 
north-south (but then again, my idea of n-s was based on my potentially 
unreliable cell phone compass).

I want to figure out the angle that the dial is twisted by so I have some kind 
of spherical geometry problem to solve. Unfortunately, I've never been able to 
get my head around spherical trig. I've tried to learn about it a few times, 
but it's still a dark art for me.

The dial is an equatorial, latitude 49.2N, 123.2W. As far as I can tell, the 
slope angle of the axis of the equatorial is correct for the latitude. As well, 
the dial base is flush to the plinth, which appears to be a properly flat 
(horizontal) surface. Today at 12:27 pm Pacific Daylight Time, the dial showed 
12:45 pm (note, although the dial shows local solar hours, the hour labels are 
advanced by one hour - like a Daylight Saving shift).

My thinking: The site is 3.2 degrees west of the timezone meridian, which is 
12.8 minutes of time, so 12:27 PDT is like 12:14.2 local mean time, or 11:14.2 
if we take out the Daylight hour. The Equation of Time is 8.3 minutes today 
(dial is fast), so the actual reading of 12:45 is like 12:36.7 local mean time, 
or 11:36.7 if we take out the Daylight hour. Hence it seems to me that the dial 
was off by 22.5 minutes of time, which is the difference between 11:36.7 and 
11:14.2.

The thing I want to know: assuming all the error is due to rotation about a 
vertical axis, what is the angle that the dial is twisted by?

Please could some kind soul help me out by explaining the steps involved in the 
calculation - my problem is in knowing which equations to use, and why.



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Re: Please help me with a calculation [SEC=UNOFFICIAL]

[Steve Lelievre]

Yep, that's it.

Steve

On 2018-09-25 6:09 PM, Hank de Wit wrote:

Is this the dial?

https://s3.amazonaws.com/gs-waymarking-images/4ac8dd87-b79b-42a0-9a14-08e86890c14d.JPG
https://c8.alamy.com/comp/AWRMGN/sun-dial-van-dusen-gardens-vancouver-bc-canada-AWRMGN.jpg



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Please help me with a calculation

[Steve Lelievre]

Hi folks,

The equatorial sundial at Vandusen Gardens in Vancouver BC is a lovely 
piece but I think it is set up wrong - I suspect the dial's axis  is not 
aligned to the meridian. This suspicion is based on the measurements 
described below, but also because when I viewed the dial today I 
concluded it is not aligned north-south (but then again, my idea of n-s 
was based on my potentially unreliable cell phone compass).


I want to figure out the angle that the dial is twisted by so I have 
some kind of spherical geometry problem to solve. Unfortunately, I've 
never been able to get my head around spherical trig. I've tried to 
learn about it a few times, but it's still a dark art for me.


The dial is an equatorial, latitude 49.2N, 123.2W. As far as I can tell, 
the slope angle of the axis of the equatorial is correct for the 
latitude. As well, the dial base is flush to the plinth, which appears 
to be a properly flat (horizontal) surface. Today at 12:27 pm Pacific 
Daylight Time, the dial showed 12:45 pm (note, although the dial shows 
local solar hours, the hour labels are advanced by one hour - like a 
Daylight Saving shift).


My thinking: The site is 3.2 degrees west of the timezone meridian, 
which is 12.8 minutes of time, so 12:27 PDT is like 12:14.2 local mean 
time, or 11:14.2 if we take out the Daylight hour. The Equation of Time 
is 8.3 minutes today (dial is fast), so the actual reading of 12:45 is 
like 12:36.7 local mean time, or 11:36.7 if we take out the Daylight 
hour. Hence it seems to me that the dial was off by 22.5 minutes of 
time, which is the difference between 11:36.7 and 11:14.2.


The thing I want to know: assuming all the error is due to rotation 
about a vertical axis, what is the angle that the dial is twisted by?


Please could some kind soul help me out by explaining the steps involved 
in the calculation - my problem is in knowing which equations to use, 
and why.


Steve


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Hour label question

[Steve Lelievre]

Today I visited a sundial that I had not viewed before.

I got myself in quite a muddle when I tried to check its technical 
quality. The first thing I looked for was a noon gap. There was none but 
I noted the noon position was labeled with a roman number I, which I 
took to mean the hours are numbered for Daylight Saving. So then, I 
looked for the 7 am and 7 pm marks to check on gnomon positioning. 
Nothing seemed right.


After a moment of confusion I realized that the numbering is not 
Daylight Saving - I had been misled by the use of roman I rather than 
XII to label the noon position. In other words, the hour labels run ... 
VIII, IX, X, XI, I, I, II, III ...


There would have been enough space to use XII as the noon hour label. Is 
the use of numeral I simply a mistake on the dial or could there be some 
other explanation?


Steve





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Re: Inauguration of the Bellingham Mural Sundial

[Steve Lelievre]

Len,

It's absolutely worth a look. Set your satnav to find the "Ciao Thyme" 
restaurant in Bellingham or use coordinates 48.753101, -122.476889. The 
mural is on the south wall of the restaurant, next to a fun Last Supper 
mural. Google Street View shows the Last Supper but not the sundial of 
course. There are a number of impressive murals in Bellingham, so take a 
walk around the city centre and Arts District while you're there.


A few years ago I told an exceptionally grumpy US border agent that I 
was going to a sundial conference, and he proceeded to quiz me in depth 
about whether I was bringing in goods for sale, and was I carrying 
commercial samples, was I was  a paid speaker, and so on. Now I just 
tell them my trips are recreational and I'm going to meet friends - 
which is also truthful. :-D


Steve



On 2018-09-23 5:44 PM, Len Berggren wrote:
Thanks for sharing this with us, Steve. (I wish I had known that there 
would be such an event so close to where I live.)


I remember Sasch sharing his dream with us at a NASS meeting some 
years ago and its realization is an event well worth celebrating! Is 
there an address (at least one nearby) so we can set our GPS on a 
sunny day and drive down to see it in all its glory?


What did US Customs and Immigration say when you told them you were 
going to see the "first shadow" of a sundial?

Len


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Inauguration of the Bellingham Mural Sundial

[Steve Lelievre]

Hello,

I offer congratulations to everyone involved in yesterday's inauguration 
of the wonderful Bellingham Mural Sundial - the huge and stunning 
south-facing vertical dial in Bellingham WA conceived by Sasch Stephens, 
that was the subject of an international design competition last year. 
The competition was won by designer and artist Gretchen Leggitt (with a 
lovely gnomon by Aaron Loveitt). Sasch and Gretchen were both there for 
the ceremony.


There was a fun and interesting program for the event (organized by 
local sundial maker Chuck //Nafziger) that included several speakers, 
musical entertainment and even a very brief juggling show (full marks 
for trying, Sasch). Woody Sullivan "unveiled" the sundial by leading a 
count down to the precise moment of solar noon.


I've posted a few photos at https://twitter.com/steve_lelievre

Cheers, Steve L.


P.S. By the way, the project is still not fully funded. Please consider 
making a donation via https://www.alliedarts.org/bellinghamsundialmural/
















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Re: Equinox Analemma

[Steve Lelievre]

Bill,

NASA has corrected the page since your post. Now it says "The featured 
analemma was composed from images taken every few days at noon".


Steve


On 2018-09-23 7:58 AM, Bill Gottesman wrote:
The NASA page says the photos were taken at 4PM, but it sure looks 
like they were taken at mean solar noon (because the analemma is 
vertical).  Does anyone have an explanation for this?


-Bill

On Sun, Sep 23, 2018 at 10:38 AM Robert Terwilliger 
mailto:b...@twigsdigs.com>> wrote:


Astronomy Picture of the Day

https://apod.nasa.gov/apod/ap180923.html

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Re: How good is a cell phone compass

[Steve Lelievre]

Hi again,

A big 'thank you' to everyone who replied to my inquiry about phone 
compasses and the setting in place of two posts. Responses are 
summarized below.


- A couple of people suggested that I should use specialist equipment 
such as theodolites or astrocompasses. Unfortunately, I neither own one 
of those nor know anyone locally who does, and the daily rental fee for 
a theodolite is well beyond my budget (~ $100 / day).


- A couple of other people suggested using a hiking compass. Since 
posting my original inquiry, I have borrowed one and, after a bit of 
fiddling around, I got it calibrated for the local magnetic declination. 
In practice, I found it difficult to use the compass for judging whether 
my two posts were lined up as required. Once I had both posts installed 
however, I got a reassuring compass reading  indicating they were 
aligned as required.


- The third approach is Kevin Karney's suggestion to use Google Earth to 
measure the position of the sundial and of a reference point, so that I 
could get a reference bearing. This, coincidentally, is a technique that 
I had referred to in a talk at last month's NASS conference; it's also 
the basis of the method I ended up using to put my second post in place 
today (but I used Google Maps). I was able to estimate the position of 
my dial very precisely and, fortuitously, Google Maps showed a 
convenient landmark exactly north of the dial location at about 30m 
distance. By standing at that landmark and using a pair of binoculars, 
it was fairly easy to line up my second post on the line to my first 
post. I had prepared a large hole in about the right place so I just had 
to call to my assistant to move the post by a centimeter  or two at a 
time, until we were happy with the placement. A light tap on a nail then 
fixed the post in place against a temporary support, and I have now set 
it in place with concrete.


With respect to the specific question of the directional accuracy 
achievable with a cell phone:


- Responses were contradictory. Richard Langley reported that he 
estimated his phone's compass to show bearings good to within about 1 
degree; I used the borrowed hiking compass to make the same comparison, 
and also found that my phone matches to within about a degree. On the 
other hand, a number of people reported having found discrepancies of up 
to 20 degrees between magnetic compass and cell phone. Clearly, the 
calibration state of the phone effects the accuracy achieved; I suspect 
the make and model does too.


- I wanted to double check the accuracy value that I had found for my 
phone. Now, it so happens that according to Google Maps a section of 
road that runs near my home is exactly North-South. My phone runs iOS; 
there is an iOS app called Theodolite that overlays the phone's camera 
with orientation information. So, I positioned myself over the edge of 
the sidewalk and used the app to sight the same edge at about 100m 
distant. It gave a bearing of 359 degrees (in one degree steps) so 
assuming the sidewalk is actually true NS, then his method also suggests 
my phone is good to about a degree.


- I have looked on the web for manufacturer's specifications, but have 
not found the required details.


- I found an academic study which suggests that a sample of 2013-era 
iPhones were found to match compasses to within about 4 degrees. The 
study mentions work by a different group who had investigated Andriod 
devices and found greater discrepancies. Note, the study relates to 
phones in use in 2013, and I don't know how relevant it would be to 
today's phones. ["Structural data collection with mobile devices" by 
Richard W. Allmendinger, Chris R. Siron, and Chelsea P. Scott / Journal 
of Structural Geology v. 102, pp. 98-112]


Cheers,
Steve














**


*From: *Steve Lelievre <mailto:steve.lelievre.can...@gmail.com>
*Sent: *September 11, 2018 12:39 PM
*To: *Sundial List <mailto:sundial@uni-koeln.de>
*Subject: *How good is a cell phone compass




How good is a cell phone compass? I mean, if I have no metal nearby and

I have the phone set to show True North, what kind of accuracy can I

expect if I lay my phone flat and use the compass app?



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Re: How good is a cell phone compass

[Steve Lelievre]

On 2018-09-11 12:49 PM, Richard Langley wrote:

There must be some specs somewhere on the Web.


Unfortunately, the only spec I've found just says the phone has an 
electronic compass - no accuracy stated.


Chat on discussion lists seems to a bit scathing but most relates to 
older phones.


Steve



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How good is a cell phone compass

[Steve Lelievre]

Hi everyone,

How good is a cell phone compass? I mean, if I have no metal nearby and 
I have the phone set to show True North, what kind of accuracy can I 
expect if I lay my phone flat and use the compass app?


I'm working on a vertical west sundial for a community garden (a.k.a 
allotment) and have a deadline of end of September to get it installed, 
because the aim is to unveil it at the group's annual meeting.


The dial is to be installed on two posts. I want to get the posts lined 
up as close to north-south as I can, to make aligning the dial easier. I 
will use adjustable bolts to fix the dial to the posts, so can I 
compensate for the line between them being a couple of degrees off - but 
no more than that.


I already have one post installed and concreted in place. I had hoped to 
use the sun's meridian shadow cast by it to give me a precise line N-S 
for placing the second post. Unfortunately, rain has set in here and it 
looks as if there will not be a sunny day for at least a week. I don't 
think I can wait that long to get the second post installed; otherwise 
I'll be short of time for the other remaining tasks. Hence my interest 
in using my phone compass for alignment.


Cheers,

Steve






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Re: EU backs ending Daylight Saving Time

[Steve Lelievre]

Jim,

Surely it's not DST all year round - it would just be the adoption of 
Atlantic Standard Time


Like Canada's wonderful Maritime Provinces, but warmer.

Steve


On 2018-08-31 6:47 AM, J. Tallman wrote:
Florida recently passed a measure that, if approved by the US 
Congress, would put the state on DST all year round!

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Re: EU backs ending Daylight Saving Time

[Steve Lelievre]

On 2018-08-31 7:31 AM, Frank King wrote:

   Commission President Jean-Claude Juncker
   said millions "believe that in future,
   summer time should be year-round, and
   that's what will happen".


I'm sure the Daily Mail will run a headline mocking the "EU bureaucracy" 
for suggesting that they can make summer last all year long.



If you look at the Greenwich meridian
you will see that it has a longer run
through France than through the U.K.

This suggests, to me(!), that both
countries should be on GMT.


Ah, but to me it suggests that the prime meridian should have been 
Paris, not Greenwich. All of Western Europe could then have had just one 
timezone!


Steve




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EU backs ending Daylight Saving Time

[Steve Lelievre]

One of the annoying parts of sundial design is having to decide whether 
to accommodate Daylight Savings Time or not, so I'm pleased to hear that 
the EU Commission is proposing to do away with it. See BBC's report at 
http://www.bbc.co.uk/news/world-europe-45366390


I hope they go through with it, and non-EU countries follow their lead.

In Canada we even have the ridiculous situation that some locales use 
DST and some do not, even within the same province. Madness!


Steve


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Re: Is this sundial business 'genuine', or not?

[Steve Lelievre]

This reminds of an interview I read somewhere, with a former RAF 
instructor who taught survival navigation techniques for downed fighter 
pilots - no GPS or compass, just sun and stars. He said that one of 
frustrating parts of his job was that with every new class he had to 
un-teach the idea drummed into them at school that the Earth goes around 
the Sun, and not the other way round. The requisite skills came much 
faster to pilots who accepted the correction.


Steve

On 2018-07-18 1:51 PM, Jack Aubert wrote:





If I were doing the curriculum I would reintroduce the geocentric view 
of the solar system to complement the Copernican view.


Jack



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Re: Is this sundial business 'genuine', or not?

[Steve Lelievre]

Sure, any type of dial is fine if it works for the situation.

And apologies to all for the typos in my last message. I think my PC had 
auto-obfuscate turned on.


Steve

On 2018-07-17 11:07 AM, Michael Ossipoff wrote:
Insisting on limiting it to central-gnomon Equatorials sounds unfair to 
students motivated to look at other dials.



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Re: Is this sundial business 'genuine', or not?

[Steve Lelievre]

An analemmatic dial is more considered more interesting than other kinds 
because it is somewhat interactive, but I agree that it is a little 
harder to understand. To me though, installing a sundial at a school 
isn't just about, or even primarily about, the teaching of the mechanics 
of how it operates.


The dial will be there for many years and seen my the whole school, not 
just the class that installs it. Its mere presence provides a point of 
interest in the schoolyard, and seeing it may well be the first time a 
child becomes aware that time can be shown by anything other than a 
clock or, more likely these days, the digital display on a microwave 
oven, TV set-top box or a cellphone.


For the class  that does the project, the laying out the dial can 
interesting and educational in itself - practicing how to measure with a 
rule, using angles, and so on. Deciding how to decorate the dial might 
be a cue for discussions about artistic composition and how to choose 
colours that work well together. Perhaps there will be a review of the 
school motto and the virtues it reflects. If the dial is made with a 
garden, there are lessons to be learned about sowing and tending plants. 
There's basic astronomy too - the opportunity for general discussion of 
the relative motion of Earth and Sun, how Earth's rotation causes night 
and day, and how seasons happen.


Trig? Projections? Some students will appreciate detailed discussion, 
but I reckon for most a quick non-technical review of the principles of 
the dial is enough.


Steve


 On 2018-07-17 9:42 AM, Michael Ossipoff wrote:


Jack--

And it seems to me that it wouldn't be satisfying, having and using a 
sundial, without a complete explanation of its construction-derivation.


You wouldn't have any trouble with the explanation. It's just that 
it's a bit long.


I suggest 3 separate discussions, preferably on subsequent days:

1. The Equatorial and Horizontal spherical co-ordinate-systems.

2. The definitions of the sine, cosine and tangent

3. The application of #2 to #1, for determining the Sun's azimuth.

That azimuth formula that that leads to directly gives the Analemmatic 
Dial's layout.


Let me just send this post now, and then (maybe this morning, probably 
this afternoon, but maybe Wednesday morning) start saying something 
about topic #1, above.


Michael Ossipoff



On Tue, Jul 17, 2018 at 9:23 AM, Jack Aubert > wrote:


I very much agree with this.  In fact, at the risk of sounding
stupid, I have to confess that I don’t have an intuitive grasp of
how an analemmatic dial works.  Yes, I have at various times gone
through the explanation, but it does not stick in any way that I
can mentally attach to the plane of the earth’s surface and the
motion of the celestial sphere.  I know I could review the
geometry and remember it if I tried but agree that the geometrical
projections involved are beyond the grasp of almost all children
and almost all adults.

Jack



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Re: Eshaness Lighthouse Sundial, Shetland, images 2

[Steve Lelievre]

Thanks everyone,

From the responses, it is clear that the dial is not original, but 
instead is a replacement probably commissioned after the property 
changed hands in 1999.


Doug Bateman's detailed photos show that the current dial is a carefully 
made instrument. The designer chose to place the gnomonic centre, the 
toe of the gnomon, to the south of the physical centre of the dial so, 
as Doug suggests, the absence of morning and evening hour labels is most 
likely from lack of space. As Doug also mentioned, his detailed photos 
show that there are indeed punch marks (and also studs on the outer 
bezel) for hours right through to midsummer sunset. Notice also that 
inside the hour labels there are screws with heads turned so that the 
slots are exactly aligned to the shadow at each hour. It suggests that 
this dial could be quite accurate.


My main question was about why some dials only show -6 to +6 local 
hours. Obviously in some cases the reason will be the one proposed for 
Eshaness - the dial may have notches or small markings for the morning 
and evening hours, but lack of space precludes labels. I also gave some 
thought to Patrick's comment about an artisan working to a template that 
only covers hours -6 to +6.


There's a good chance anyone in the UK looking for practical information 
on sundial design in the 1990s, might end up working from Cousins' book 
(I believe both Mayall & Mayall and Waugh were American publications 
which, coupled with the timing of the various editions and 
reprints,means they were less likely to have made it into library 
collections in the UK). Cousins provides 4 methods for laying out a 
horizontal dial: by use of an equatorial disk, by graphical 
construction, by trig., and by use of tables of hour line angles (½° 
steps in latitude). It turns out that in each case he only addresses the 
hours -6 to +6 (even though some of the photo illustrations do show 
morning and evening hours) so he may have spawned or perpetuated the 
practice of limiting the dial to 12 hours. An artisan following any of 
the 4 methods without understanding the principles, would be unable to 
fill in the other hours. As well, because the book discusses -6 to +6 
only, it could somehow legitimize those limits in the the mind of the 
reader.


Lastly, it's interesting to learn that lighthouse keepers needed a 
carefully calibrated clock to know when to light their lanterns. The 
naive assumption would be that they simply lit up as darkness approached 
- which would be around sunset or soon after, dependent on how dark the 
clouds were that evening.


Steve



On 2018-07-13 7:14 AM, Douglas Bateman wrote:

Steve, et al,

Concerning the dial itself, it looks as if a second plate has been 
added. It has the unusual detail of numerals in relief, there are 
small screw heads adjacent to each set of numerals, and the gnomon is 
indeed non-standard compared with other Scottish lighthouse dials.


Close examination reveals what looks like a dial underneath, and its 
periphery marked with hours and 15 minute punch marks. Closer still 
and I am convinced that each cut-out numeral has been screwed in place 
from countersunk (?) screws from below.


I can confirm that the small plaque was very corroded, and the lack of 
‘extra’ hours may have been to avoid overcrowding near the plaque with 
the added-on numerals, although there are outer punch marks for the 8 
o’clock hours.


Regards, Doug


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Re: Blank subject line

[Steve Lelievre]

The apparent lack of a subject line is not always the sender’s control.
There is some interaction between the sender’s email system and the sundial
listserv software meaning that some messages arrive in our mailboxes aa
forwarded items. These items do not show a subject line when you first look
at them, but the sender’s subject line is in the text of the message.

Messages affected this way show ‘via sundial’ after the sender name:; at
least on my email client software.

So, messages are not spam if they show ‘via sundial’.

Steve

On Tue, May 22, 2018 at 07:33, Roger W. Sinnott 
wrote:

> I agree with Helmut!
>
> When I see a blank subject line, I become suspicious and often just delete
> the message without opening it.
>
> Roger
>
>
> -Original Message-
> From: sundial [mailto:sundial-boun...@uni-koeln.de] On Behalf Of Helmut
> Haase
> Sent: Tuesday, May 22, 2018 10:11 AM
> To: sundial@uni-koeln.de
> Subject: Blank subject line
>
> Hallo gnomonicist,
> It seems to become a trend here to send mails without subject information.
>
> Is it difficult to write a subject line?
>
> Regards
>
> Helmut Haase
>
>
>
> ---
> https://lists.uni-koeln.de/mailman/listinfo/sundial
>
> ---
> https://lists.uni-koeln.de/mailman/listinfo/sundial
>
> --
Cell +1 778 837 5771
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"Sunny Side Up"

[Steve Lelievre]

For if you happen to have a spare robotic arm lying around ...

https://vimeo.com/268950472



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Re: sundial Digest, Vol 149, Issue 3

[Steve Lelievre]

Hi, Lupe,

There are several cities called Elizabethtown in the USA  - the one that 
Ken's message relates to is in the state of Pennsylvania (PA is a 
standard abbreviation for Pennsylvania).


Wikipedia: https://en.wikipedia.org/wiki/Elizabethtown,_Pennsylvania
Google Maps: https://goo.gl/maps/v7hccZvXSrR2

Cheers, Steve


On 2018-05-03 10:09 PM, Lupe F. wrote:

Dear Ken Clar,
Where is Elizabeth town, PA?

Thanks


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New version of 'gmath' available

[Steve Lelievre]

I have prepared a new version of /gmath/, the gnomonics add-on for 
Microsoft Excel that was announced in NASS' Compendium 24:4 (December 2017).


Documentation for the new version is available as a PDF file at 
http://va7lel.ca/sundial/gmath.pdf


The updated Excel Add-In is available for download from 
http://va7lel.ca/sundial/gmath.xlam


Existing installations can be updated by overwriting the gmath.xlam file 
in your Microsoft Add-Ins folder (see documentation). You must do it 
while Excel is _not_ running.


_Bug fix_

Values returned by the functions /geot/ and /gdcl/ were systematically 
wrong. When compiling the associated tables, I forgot to specify noon as 
the required time of day, meaning the functions always returned values 
applicable to the previous midnight. In the case of Equation of Time 
values returned by /geot/, this resulted in an error of less than about 
0.1 seconds. In the case of solar declination returned by /gdcl/, the 
discrepancy was insignificant at the solstices but as much as 0.2 
degrees near the equinoxes. The functions /geoted/ and /gdcled/ were not 
affected by the bug.


_Other changes_

Functions based on formulae involving the obliquity of the elliptic now 
include an adjustment for nutation. For ordinary sundialing purposes the 
change is insignificant: the new obliquity values differ from the 
originals by only about 9 arcseconds.


The new version retains an existing circumvention for a deficiency in 
Excel 2011 for Mac which led to failure of some gmath functions.



Cheers,

Steve Lelievre


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Re: Zenith angles and hours to sunset

[Steve Lelievre]

Willy, thanks.

I'm travelling away from home now, so can't respond in full - but your 
chart helps me and gives me an idea that I will combine with Gian's rule 
of thumb and post on the list later.


Steve

On 2017-11-08 10:10 AM, Willy Leenders wrote:

Hello Steve,

Based on your discovery and to prove that from the vernal equinox to 
the autumnal equinox for a certain time to sunset the sun altitude is 
*/approximately/* equal, I made calculations and a graph showing that 
this is the case for 1, 2, 3 and 4 hours to sunset.


Willy Leenders
Hasselt in Flanders (Belgium)

Visit my website about the sundials in the province of Limburg 
(Flanders) with a section 'worth knowing about sundials' (mostly in 
Dutch): http://www.wijzerweb.be





Op 6-nov-2017, om 02:15 heeft Steve Lelievre het volgende geschreven:

I have been doing some calculations for an Hours To Sunset dial (that 
is, an Italian Hours dial with the numbering running backwards). I 
discovered that the maximum altitude for a given hour does not occur 
at the summer solstice.  I was a little surprised to discover this - 
not amazed, but surprised enough to make me wonder if I have done my 
calculations wrong.


The attached diagram is for the example case of 4 hours before 
sunset. I'm getting a double maximum occurring a little after the 
vernal equinox and a little before before the autumnal equinox. I get 
similarly shaped curves for others hours, with less separation 
between the peaks when I use higher (italian) hour numbers.


Assuming that I have in fact graphed the altitude correctly, it means 
is that there is a period over the summer months when the altitude 
for any given hour to sunset stays /approximately/ the same. In my 
case, at 49N, it seems that over the summer months, the solar 
altitude for 1 hour to sunset is approximately a little under 10 
degrees, 2 hours to sunset is approximately a little under 20 
degrees, and so on at a little under 10 degrees per hour, at least 
for the last 5 to 6 hours of the day.


In this day and age, I think we would demand greater accuracy, but 
have there ever been sundials or other devices that exploited this 
approximation?


Steve


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Re: Zenith angles and hours to sunset

[Steve Lelievre]

Thanks, Gian, for validating my calculations, and for that story.  It 
must be based on the rule of thumb that the thickness of a finger (or 
maybe a thumb?) is 2 degrees. For my latitude, that would mean that each 
fist is about one hour to sunset.  I must remember to try it next summer.


Cheers,
Steve






On 2017-11-06 12:28 AM, Gian Casalegno wrote:

A similar result can be obtained by means of Orologi Solari.

The attached pdf shows a dial at 49.2 N where hours to sunset lines 
and sun height lines are drawn.
The asymptotes of the sun height lines are parallel to the hour lines 
in the afternoon i.e. sun height is nearly constant for a fixed time 
to sunset value.


The attached image shows a shepherd dial with the last seven time to 
sunset lines drawn.
Hour lines 1 to 5 are nearly horizontal in the right side of the graph 
(summer).

The result is so again confirmed.

Therefore time to sunset can be deduced in summer from the height of 
the sun on the horizon.


This fact reminds me about a trick that someone told me a long time ago.
It was said that sailors used to estimate the time by measuring with 
their fingers the height of the sun above the line of the horizon.
I always thought it was a fake but now I see it can work, at least in 
the evening in summer time.

Of course the relation between height and time depends on the latitude.

Ciao.
Gian


<https://www.avast.com/sig-email?utm_medium=email_source=link_campaign=sig-email_content=webmail> 
	Mail priva di virus. www.avast.com 
<https://www.avast.com/sig-email?utm_medium=email_source=link_campaign=sig-email_content=webmail> 




2017-11-06 2:15 GMT+01:00 Steve Lelievre 
<steve.lelievre.can...@gmail.com 
<mailto:steve.lelievre.can...@gmail.com>>:


I have been doing some calculations for an Hours To Sunset dial
(that is, an Italian Hours dial with the numbering running
backwards). I discovered that the maximum altitude for a given
hour does not occur at the summer solstice.  I was a little
surprised to discover this - not amazed, but surprised enough to
make me wonder if I have done my calculations wrong.

The attached diagram is for the example case of 4 hours before
sunset. I'm getting a double maximum occurring a little after the
vernal equinox and a little before before the autumnal equinox. I
get similarly shaped curves for others hours, with less separation
between the peaks when I use higher (italian) hour numbers.

Assuming that I have in fact graphed the altitude correctly, it
means is that there is a period over the summer months when the
altitude for any given hour to sunset stays /approximately/ the
same. In my case, at 49N, it seems that over the summer months,
the solar altitude for 1 hour to sunset is approximately a little
under 10 degrees, 2 hours to sunset is approximately a little
under 20 degrees, and so on at a little under 10 degrees per hour,
at least for the last 5 to 6 hours of the day.

In this day and age, I think we would demand greater accuracy, but
have there ever been sundials or other devices that exploited this
approximation?

Steve


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Zenith angles and hours to sunset

[Steve Lelievre]

I have been doing some calculations for an Hours To Sunset dial (that 
is, an Italian Hours dial with the numbering running backwards). I 
discovered that the maximum altitude for a given hour does not occur at 
the summer solstice.  I was a little surprised to discover this - not 
amazed, but surprised enough to make me wonder if I have done my 
calculations wrong.


The attached diagram is for the example case of 4 hours before sunset. 
I'm getting a double maximum occurring a little after the vernal equinox 
and a little before before the autumnal equinox. I get similarly shaped 
curves for others hours, with less separation between the peaks when I 
use higher (italian) hour numbers.


Assuming that I have in fact graphed the altitude correctly, it means is 
that there is a period over the summer months when the altitude for any 
given hour to sunset stays /approximately/ the same. In my case, at 49N, 
it seems that over the summer months, the solar altitude for 1 hour to 
sunset is approximately a little under 10 degrees, 2 hours to sunset is 
approximately a little under 20 degrees, and so on at a little under 10 
degrees per hour, at least for the last 5 to 6 hours of the day.


In this day and age, I think we would demand greater accuracy, but have 
there ever been sundials or other devices that exploited this approximation?


Steve

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Re: Great Circle Studios webpage gone?

[Steve Lelievre]

Thanks to everyone who responded, on and off-list, to my inquiry about 
Great Circle Studio's web site. I used that web site because it had a 
facility for getting solar position data in a tabulated layout, at a 
chosen interval over a chosen date range (such as daily values  over a 
year). It was easy to move the table of data to other software for 
further processing.


Unfortunately, the clone of the Great Circle Studio webpage, as found by 
Googling, is not functional. It seems that someone ripped the original 
webpage but did not realize (and did not test) that the page is just a 
web form that has to be submitted to a server in order to generate the 
result data.


The alternative tools that respondents suggested are all very good, but 
the one that seems best suited to my specific purpose is the SPA [Solar 
Position Algorithm] Calculator hosted by the US National Renewable 
Energy Laboratory at http://midcdmz.nrel.gov/solpos/spa.html. It is very 
powerful, but has a small deficiency - the maximum interval allowed is 
60 minutes, so if you want daily (noon) figures you must generate a year 
of hourly data and then discard most rows from the table of results.


Thanks again, all.

Steve
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Great Circle Studios webpage gone?

[Steve Lelievre]

I've tried to access the Great Circle Studio's solar data calculator a 
couple of time recently, but the website seems to be unavailable. Can 
anyone tell me if it's permanently gone, as opposed to suffering a 
temporary problem?


I'll miss it if it is gone... it is/was a great site for getting solar 
position and EoT data.


Steve




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Re: Golden Ratio and Sundials

[Steve Lelievre]

On Thu, Jun 22, 2017 at 12:31, Donald L Snyder  wrote:

> Since
> atan(1.61803) equals 58.28 degrees, a horizontal sundial in a city at
> this latitude could have a triangular gnomon with a height to base
> ratio that is golden.
>Don Snyder
>
> On 6/21/2017 10:00 PM, Michael Ossipoff wrote:
>
>
>
> On Wed, Jun 21, 2017 at 5:27 PM, Brooke Clarke  wrote:
>
>> Hi Roderick:
>>
>> I also have a book on this number that makes the case that there is no
>> such ratio.
>>
>
>
> Your book is mistaken.
>
> If A/B = (A+B)/A, then A/B is the golden ratio.
>
> If a line-segment is divided into two parts related by that ratio, then
> the golden ratio is also called the golden section.
>
> If the interval between two numbers is divided into two intervals related
> by the golden ratio, then the golden ratio is also called the golden mean.
>
>
>
>> For example if you look at a photograph of something where do you put the
>> markers to make the measurement?
>>
>
> Along two mutually-perpendicular edges, measured from a common corner?  :^)
>
>
> Michael Ossipoff
>
>
>
>> Brooke 
>> Clarkehttp://www.PRC68.comhttp://www.end2partygovernment.com/2012Issues.html
>>
>>  Original Message 
>>
>> Hi all,
>>
>> I have been reading a book on the Golden Ratio which is 1.6180339887. It
>> describes how the Golden Ratio describes how the spiral of a sea shell is
>> produced. And how nature uses the Golden Ratio on the size of leaves etc.
>>
>> Does anyone know if sundials have ever been produced useing the Golden
>> Ratio. The Golden Ratio goes back in history so one wonders if it was ever
>> applied to sundials.
>>
>> The book describes that the short and long sizes of credit cards are
>> close to being the Golden Ratio.
>>
>> LongSide/ShortSide = Golden Ratio.
>>
>> Regards,
>>
>> Roderick Wall.
>>
>>
>>
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>>
>>
>>
>> ---
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>>
>>
>>
>
>
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Re: Inquiry - Part 1

[Steve Lelievre]

Dear Frank,

You're right - the timeline casts doubt on the premise of the enquiry. 
Well spotted!


For anyone who's interested, here's a snippet from/Enclopaedia 
Britannica/ (7th ed.)


"The first [Equation Clock] was made about the year 1693 by Mr Joseph 
Williamson, an English artist then working for Mr Daniel Quare 
watchmaker in London, who sold it to go to Charles II King of Spain 
about the year 1699. It went 400 days with one winding and had two fixed 
and two movable circles for the hands to mark the time on : the former 
giving the hours and minutes of mean time; and the latter, which were 
concentric with the former, apparent time. [...] Father Alexandre, a 
Benedictine, had laid a project of this sort before the Academy of 
Sciences in 1698 which is mentioned in their Memoirs for 1725 but 
nothing of the kind seems to have been practised in France till a clock, 
the equation work of which scarcely differed from Williamson's, was made 
by Lebon in 1717. This was soon after followed by another by Leroy."


I found a 1737 publication /Regle artificielle du temps /by Henry Sully, 
an English clockmaker in Paris and clockmaker to the Duc D'Orleans, 
which has fairly extensive instructions on how to regulate clocks using 
either a sundial or by observing transits of stars,  and how to convert 
a mean time reading to solar time by use of Equation of Time tables. I 
didn't notice any mention of equation clocks when I looked through 
Sully's treatise, so I assume they remained rather rare even 20 years 
after Le Bon and Le Roy had introduced them.


Thanks to everyone who has responded to my enquiries.

Steve



On 2017-04-26 5:44 AM, Frank King wrote:

Dear Steve,

I have read the replies to your enquiry and I
am not yet convinced by the responses to either
Part 1 or Part 2!

I'll restrict myself to Part 1, where it is
asserted...

...that Louis XIV issued some kind of edict
that all clocks manufactured in France were
to be Equation Clocks (that is, clocks that
showed solar time through a mechanical
Equation of Time 'reversal' adjustment).

One point of note is that Louis XIV reigned
from 1643 to 1715 so this edict must have been
sometime in those 72 years.

Roderick Wall's reference...

https://books.google.com.au/books?id=d1oUQAAJ=PA462=PA462=all+clo
cks+manufactured+in+France+were+to+be+Equation+Clocks=bl=ih4yWalJ9E&
sig=6u-sTxpfyTqZNPxRjfbAn7Q_ECk=en=X=0ahUKEwjW9oruqrbTAhVEGJQKHU-NDrs
Q6AEIIzAD#v=onepage=all%20clocks%20manufactured%20in%20France%20were%20to%20b
e%20Equation%20Clocks=false

says on page 462...

Equation clocks were first made in France,
about the year 1717, by Le Bon and Le Roy.

It seems unlikely that Louis XIV could have
insisted on something that didn't exist in
his time.

As king, Louis XIV no doubt had up-market
clocks in his palaces and he could simply
have instructed his clock-keepers to set
the clocks using a convenient sundial.

The solar day typically differs from 24 modern
hours by a small fraction of a minute and it
is unlikely that the clocks early in his reign
kept time to anything like that precision.
Frequent setting to sundial time would have
been required.

When he upgraded to pendulum clocks he may
have noticed that his clock-keepers had
changed their procedures...

I think the first EoT tables used for
"correcting" clocks were published by
Huygens in 1665 and better tables were
published by Flamsteed about 7 years
later.

Enthusiastic clock-keepers may have used
these tables and the king may not have
approved.  The only edict that he need
have issued would have been of the form:

   "Do not use the equation of time when
setting the clocks."

I know how to dig out ancient English Acts
of Parliament but I do not know how to find
old French edicts.

  Please can someone nail down this edict?

Until I can read this edict in 17th century
French, I shall deem this to be another
example of a much-repeated falsehood
gaining widespread acceptance.

Now to ponder part 2!

Frank

Frank H. King
Cambridge, U.K.




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Inquiry

[Steve Lelievre]

Hi,

I've got a two part inquiry from a third party:

1. Is it true that Louis XIV issued some kind of edict that all clocks 
manufactured in France were to be Equation Clocks (that is, clocks that 
showed solar time through a mechanical Equation of Time 'reversal' 
adjustment). References sought.


2. Can anyone confirm that throughout the 19th centuary (and perhaps 
into the early 20th centuary?), the French railways system used 
heliochronometers installed at each station for daily calibration of 
station clocks? Again, references sought.


Thanks,
Steve


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Re: Dial face colouration

[Steve Lelievre]

John, thanks for the clarification, and your patience with my questions.

All, I'm off to buy some photographic mattes to do experiements with. 
This is all about having a horizontal dial face that is not too bright 
to view even in the summer midday sun - so I'll go quiet now and report 
back after the summer solstice.


Steve



On 2017-02-28 1:40 AM, John Lynes wrote:

Hi Steve,
I'm sorry I've confused you.

...
The take-home conclusion is that there is no single ideal reflectance 
for the plate of a sundial.  It varies with the sky illuminance.  When 
Weber's Law prevails, a reflectance of about 60 per cent is likely to 
be a safe bet.


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Re: Dial face colouration

[Steve Lelievre]

John,

Will you clarify some things for me?

You mention that 50 lumens per square foot is about 500 lux, and that 
the cited article recommends a limit of 60% reflectance for sky 
illuminance of up to 1,000 lumens per sq. ft. If I multiple all that 
out, it would appear to suggest a a limit of 6,000 lux of reflected 
light for comfortable viewing. Is that the case?


Through Google, I found empirical rules for calculating the wattage of 
solar radiation reaching the ground, depending on season, altitude, 
declination, hour angle, and geographic elevation. I also found a 
conversation factor for converting sky illumination in watts per square 
metre to lux. Putting it all together, I get a figure of about 72,000 - 
91,000 lux for the incident illumination,  at noon on the northern 
hemisphere summer solstice at sea level, depending on latitude (and 
valid for mid-latitudes only). Using the mid figure of 80,000 lux, if I 
want to limit the reflected light to 6,000 lux then the reflectivity has 
to be less than 22.5%, which corresponds to a lightness of only 3.5 on 
the Munsell scale.


Does this conversion make sense, or don't things work like that?

Of course, if we've gone out in midday sun, we should be wearing 
sunglasses and, again from the web, sunglasses reduce the visible light 
reaching our eyes by two thirds or more. If I factor that in, my Munsell 
value rises to 5.3. And, as you pointed out, when the sun isn't so high 
in the sky, we can tolerate a more reflectivity on our dial face.


Thanks for any further comments or advice,

Steve

P.S. Based on what I've learned so far, I'm leaning towards using a 
material with a Munsell value of 6 or 7, which would correspond to the 
mid-grays, tans and browns that people have been suggesting may work in 
practice. It would be the number you mentioned but with the lightness 
notched down a little. My design latitude of 45N is a little further 
south than England (where the article's authors came from) and the 
summer sun is a tad brighter. As well, I reckon a suitable colour with a 
number of 6 or 7 would look OK against a lawn, flowerbed or other greenery.




On 2017-02-26 7:08 AM, John Lynes wrote:
There is no single optimum reflectance for a flat dial face.  
Obviously under dim sunlight the optimum reflectance would be 100 per 
cent, i.e.perfect white.
Under intense sunlight, contrast sensitivity would be optimised for a 
lower value of reflectance.  Thousands of papers have been written on 
contrast sensitivity.  One classical study is "Brightness and contrast 
in illuminating engineering" by RG Hopkinson, WR Stevens and JM 
Waldram, Transactions of the Illuminating Engineering Society 
(London), Vol 6, No 3, pp 37-48 (1941). This indicates that when the 
sky illuminance on a matt dial face is over about 50 lumens per square 
foot (about 500 lux) the optimum reflectance would be about 60 per 
cent (a light grey, about Munsell Value 8).  Below this illuminance 
(which would correspond to a solar altitude close to sunrise or 
sunset) the optimum reflectance would rise quite sharply.
Note however that the maximum sky illuminance considered by the 
authors was 1000 lumens per square foot (corresponding to a solar 
altitude of about 20 degrees).  Higher illuminances might further 
reduce the optimum reflectance.

John Lynes


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