Re: Adjusting dial to new location

[Michael Ossipoff]

By “auto-correction”, I refer modification of the dial, so that it will
directly read Local-True-Solar-Time (LTST) at your latitude at your
standard-meridian instead of where the dial is.

…

Auto-correcting for longitude by rotating & tipping the dial is a
“retrofit” longitude auto-correction, as opposed to initially incorporating
that auto-correction in the marking of the dial.

…

(As I said, I have no idea why anyone would want longitude-auto-correction,
to make the dial read the Local-True-Solar-Time (LTST) at your latitude at
your timezone’s standard-meridian (instead of where the dial is). Because
the longitude-correction could be achieved by merely adding the
longitude-correction constant to each EqT entry on the correction-plaque,
the auto-correction doesn’t avoid any table-consulting & correction work
needed by the dial-user who wants standard-time.  All it accomplishes is to
make LTST determination require a correction too.)

…

As has already been pointed out twice, only one wedge is needed.

…

The longitude-correction could be achieved by, first, an initial rotation
about the vertical axis, & then a rotation about some particular horizontal
axis.

…

Three variables:

…

1. The amount & direction of initial rotation, about the vertical-axis,
away from the NS alignment of the gnomon.

…

2. The place on the circular-dial-plate’s circumference at which the wedge
is applied.

…

3. The amount by which the dial-plate is tipped by that wedge.

…

There are three desiderata:

…

1. The style is in the meridianal-plane, with its higher end poleward.

…

2.The Style is tipped above the horizontal by an angle equal to the
latitude.

…

3. The dial has been rotated about the style so as to have the orientation
of flat ground at your standard-parallel.at your latitude. (i.e. rotated in
the direction of your standard meridian, by the number of degrees by which
that meridian differs from yours.)

…

Those 3 desiderata give 3 equations in 3 unknowns. The 3 variable are the
unknowns.

…

The equations are spherical co-ordinate-transformation formulas. The 3
equation are statements, in terms of those formulas, that the 3 desiderata
are achieved.

…

The 3 nonlinear equations in 3 unknowns can be numerically-solved by the
Newton-Raphson method,  In fact according to some authors, Newton-Raphson
is the only method available for a system  of nonlinear equations.

…

You speak of rotation about 3 axes. …2 of them by wedges?  (…because you’ve
suggested 2 wedges.).

,,,

When the 1st wedge is put in at (say) the dial-plate’s north edge, the dial
plate is supported by, & stably balanced on, the wedge at the dial-plate’s
north edge, & the dial edge opposite the wedge, at the south edge of the
dial-plate. That means that the whole dial-plate & all of its periphery
(except its south-point) are above the horizontal table-surface on which
the dial was resting.

…

Now, when you put a 2nd wedge in at (say) the dial-plate’s east edge, &
push it in till it contacts the raised dial-edge, & then & start rotating
the dial-plate with it, about what axis are you rotating the
dial-plate?  You’re
rotating it about the line drawn between the point at the dial-plate’s
south edge, where the dial-plate rests on its horizontal table, & some
point on the west edge of the wedge at the north end of the dial.

…

That isn’t a horizontal axis.

…

I guess you could do it that way, but it sounds like more work than the use
of just one wedge.

…

As I said, you only need one wedge.

…

Your other suggestion expressed after that is unclear.

On Tue, Apr 4, 2023 at 7:38 PM  wrote:

> Depending on your choice of rotation axes, only two rotations are needed,
> one for the elevation of the pole and one around the gnomon for longitude
> correction. These are the two that correspond to the actual changes needed.
>
> If you are using the three orthogonal x, y, and z axes, then three
> rotations are needed. And they can tell you how to make the wedge.
>
> Another three rotation procedure that might be easier to understand but
> may not tell you how to make the wedge is this. Rotate about a horizontal
> axis until the gnomon is vertical. Now rotate around the vertical axis to
> include the longitude correction. Then rotate around a horizontal axis to
> put the gnomon in the correct new location. I would do this in a computer
> graphics situation because it only requires the old and new position values.
> ---
>
>
>
> On 2023-04-04 15:54, Steve Lelievre wrote:
>
>
> 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 becaus

Re: Adjusting dial to new location

[koolish]

Depending on your choice of rotation axes, only two rotations are
needed, one for the elevation of the pole and one around the gnomon for
longitude correction. These are the two that correspond to the actual
changes needed. 


If you are using the three orthogonal x, y, and z axes, then three
rotations are needed. And they can tell you how to make the wedge. 


Another three rotation procedure that might be easier to understand but
may not tell you how to make the wedge is this. Rotate about a
horizontal axis until the gnomon is vertical. Now rotate around the
vertical axis to include the longitude correction. Then rotate around a
horizontal axis to put the gnomon in the correct new location. I would
do this in a computer graphics situation because it only requires the
old and new position values.

---

On 2023-04-04 15:54, Steve Lelievre wrote:

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

[koolish]

Assuming that a dial should read only local solar time is a rather
limited view. While it might be of interest to the dial purist, it is
not particularly useful to the general population and often requires a
lot of explanation. And it makes us seem like an eccentric clique. The
dial produces a shadow. The hour lines and other indications are
strictly our interpretation and a particular one should not be forced on
everybody else.

---

On 2023-04-04 13:05, Michael Ossipoff wrote:

On Tue, Apr 4, 2023 at 08:45  wrote: 

Rotating the dial plate around a vertical axis is wrong because the hours lines are not at constant angles. 

Rotating the whole dial around the polar axis is the correct way to adjust a local solar time dial to a different longitude, the time zone center, for example. 


Having a dial show the time in a different location is strictly a creative 
choice.

---

Rotating the dial about the vertical axis & then doing the non-meridian Al 
tipping, in the right combination, is how you get the result that the dial is 
oriented (still in the meridianal-plane) to give Local True Solar Time at your 
standard meridian.


I don't know why anyone would want to do that, unless it's important to keep using an old EqT plaque. 

On 2023-04-04 08:44, Jack Aubert via sundial wrote: 
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eigentliche Nachricht steht dadurch in einem Anhang.

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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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Fwd: Adjusting dial to new location

[Michael Ossipoff]

-- Forwarded message -
From: Michael Ossipoff 
Date: Tue, Apr 4, 2023 at 09:53
Subject: Re: Adjusting dial to new location
To: 


The combination of rotation about the vertical axis, &  then non-meridianal
tipping, hadn’t occurred to me.

…to directly read the Local True Solar Time of somewhere else.

…so that you can just use your old EqT plaque after you move?

Wouldn’t have occurred to me. I’d just make a table incorporating EqT & the
new longitude- correction.

I wouldn’t want a sundial to be committed to clock-time, by building in the
longitude correction (either when marking the dial, or by the rotation &
tipping).


On Tue, Apr 4, 2023 at 08:45  wrote:

> Rotating the dial plate around a vertical axis is wrong because the hours
> lines are not at constant angles.
>
> Rotating the whole dial around the polar axis is the correct way to adjust
> a local solar time dial to a different longitude, the time zone center, for
> example.
>
> Having a dial show the time in a different location is strictly a creative
> choice.
> ---
>
>
>
> On 2023-04-04 08:44, Jack Aubert via sundial wrote:
>
> Diese Nachricht wurde eingewickelt um DMARC-kompatibel zu sein. Die
> eigentliche Nachricht steht dadurch in einem Anhang.
>
> This message was wrapped to be DMARC compliant. The actual message
> text is therefore in an attachment.
>
> ---
> https://lists.uni-koeln.de/mailman/listinfo/sundial
>
> ---
> https://lists.uni-koeln.de/mailman/listinfo/sundial
>
>
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Re: Adjusting dial to new location

[Michael Ossipoff]

The public stationary sundial in my town is mounted normally for Local True
Solar Time. It’s correction-plaque gives un-adjusted EqT, with an
instruction to add a certain number of minutes for the longitude-correction.

On Sun, Apr 2, 2023 at 17:26 Steve Lelievre 
wrote:

> 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
>>
>>
>> ---
>> https://lists.uni-koeln.de/mailman/listinfo/sundial
>>
>>
>> ---https://lists.uni-koeln.de/mailman/listinfo/sundial
>>
>> --
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Re: Adjusting dial to new location

[Michael Ossipoff]

On Tue, Apr 4, 2023 at 08:45  wrote:

> Rotating the dial plate around a vertical axis is wrong because the hours
> lines are not at constant angles.
>
> Rotating the whole dial around the polar axis is the correct way to adjust
> a local solar time dial to a different longitude, the time zone center, for
> example.
>
> Having a dial show the time in a different location is strictly a creative
> choice.
> ---
>
>
> Rotating the dial about the vertical axis & then doing the non-meridian Al
> tipping, in the right combination, is how you get the result that the dial
> is oriented (still in the meridianal-plane) to give Local True Solar Time
> at your standard meridian.
>

I don’t know why anyone would want to do that, unless it’s important to
keep using an old EqT plaque.

> On 2023-04-04 08:44, Jack Aubert via sundial wrote:
>
> Diese Nachricht wurde eingewickelt um DMARC-kompatibel zu sein. Die
> eigentliche Nachricht steht dadurch in einem Anhang.
>
> This message was wrapped to be DMARC compliant. The actual message
> text is therefore in an attachment.
>
> ---
> https://lists.uni-koeln.de/mailman/listinfo/sundial
>
> ---
> https://lists.uni-koeln.de/mailman/listinfo/sundial
>
>
---
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Re: Adjusting dial to new location

[koolish]

Rotating the dial plate around a vertical axis is wrong because the
hours lines are not at constant angles. 


Rotating the whole dial around the polar axis is the correct way to
adjust a local solar time dial to a different longitude, the time zone
center, for example. 


Having a dial show the time in a different location is strictly a
creative choice.

---

On 2023-04-04 08:44, Jack Aubert via sundial wrote:


Diese Nachricht wurde eingewickelt um DMARC-kompatibel zu sein. Die
eigentliche Nachricht steht dadurch in einem Anhang.

This message was wrapped to be DMARC compliant. The actual message
text is therefore in an attachment. 
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RE: Adjusting dial to new location

[Jack Aubert via sundial]

Diese Nachricht wurde eingewickelt um DMARC-kompatibel zu sein. Die
eigentliche Nachricht steht dadurch in einem Anhang.

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text is therefore in an attachment.--- Begin Message ---
I think I must be missing something here.  I cannot quite wrap my brain around 
what we would be trying to accomplish with a longitude adjustment.

 

A horizontal garden variety dial should tell apparent local solar time as long 
as it is correctly designed and the gnomon is pointing at the north celestial 
pole.  It can be moved to a new location and will continue to tell apparent 
local solar time as long as the whole thing is tilted so that it is at the 
latitude it was designed for and positioned so that the gnomon continues to 
point to the north celestial pole.  Now, If such a dial were to be tilted on 
its other axis so that it corresponds to the original longitude then I think it 
would tell local solar time at the original longitude.  This would appear to be 
wrong since it would not correspond to either local solar time or local civil 
time.   

 

AFAIK, the only way longitude comes into play in the design would be to make 
the dial conform more closely to civil time (leaving aside the equation of 
time) for example if the dial is located near the edge of the time zone.  AFAIK 
the only way to do this is to shift the dial plate around the vertical axis 
originating at the bottom end of the gnomon so that noon is no longer lined up 
with the gnomon and east west are no longer at right angles to the gnomon.  If 
such a dial were relocated then it would need some kind of longitude adjustment 
but would it not then tell something approximating civil time at its old 
location rather than the new one?

 

Is this wrong?  Is it possible to make a local longitude adjustment by tilting 
the whole thing on its polar axis?  

 

My spherical trig is almost nonexistent so I am trying to imagine all this 
visually and cannot quite see how it would work.  It seems to me that an 
east-west wedge would throw the gnomon off its polar axis.  

 

Jack Aubert  

 

 

From: sundial  On Behalf Of Steve Lelievre
Sent: Monday, April 3, 2023 7:47 PM
To: Rod Wall ; kool...@dickkoolish.com
Cc: 'Sundial sundiallist' 
Subject: Re: Adjusting dial to new location

 

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.



 

--- End Message ---
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Re: Adjusting dial to new location

[Rod Wall]

Hi Steve,

I use to be a member of the NASS but I am retired now. And due to funds 
I was not able to renew my membership. So I don't have access to Fred 
Sawyer's and Bill Gottesman's article.


Maybe the Article and the drawing of the Earth with sundials could be 
used to explain this?


Roderick.

On 3/04/2023 10:26 am, Steve Lelievre wrote:
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
 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

[Rod Wall]

Hi all,

Is the Sundial Mailing list able to accept images?

Below is how we can understand how sundials work. A sundial is a 
mechanical clock. Sundials are geared to the largest clock in the world, 
Earth. Look at it from a mechanical point of view on a spinning Earth.


Draw the earth and cut out paper sundials and place them at different 
Longitudes and see what wedge is needed to keep the style parallel to 
the axis of the Earth.


You can also understand how sundials work in the southern hemisphere. 
The sun still comes up in the East and sets in the West.


Roderick.

On 4/04/2023 12:03 pm, Michael Ossipoff wrote:
That surprises me too. I’d have expected that the only differences 
would be that the dial is numbered counterclockwise, & that north & & 
south are replaced with poleward & equatorward.


On Mon, Apr 3, 2023 at 16:47 Steve Lelievre 
 wrote:


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

[Rod Wall]

Hi all,

This link I think is a good way of showing. How we can understand how 
sundials work. A sundial is a mechanical clock. Sundials are geared to 
the largest clock in the world, Earth. Look at it from a mechanical 
point of view on a spinning Earth.


Draw the earth and cut out paper sundials and place them at different 
Longitudes and see what wedge is needed to keep the style parallel to 
the axis of the Earth.


https://www.dropbox.com/s/5loieb818s2dr9o/CCF%20Relocating%20a%20sundial%204%20April%202023.pdf?dl=0

You can also understand how sundials work in the southern hemisphere. 
The sun still comes up in the East and sets in the West.


Roderick

On 4/04/2023 12:03 pm, Michael Ossipoff wrote:
That surprises me too. I’d have expected that the only differences 
would be that the dial is numbered counterclockwise, & that north & & 
south are replaced with poleward & equatorward.


On Mon, Apr 3, 2023 at 16:47 Steve Lelievre 
 wrote:


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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