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

[Michael Ossipoff]

Patrick--

That isn't necesary, because sundials are for telling solar time, not clock
time.

If you want Standard-Time, then a conversion table, incorporating EqT &
longitude-adjustment, can be used.

Michael Osslipoff
July 31st
Week 32, Wednesday
0540 UTC


On Tue, Jul 30, 2019 at 3:17 PM Patrick Vyvyan 
wrote:

> A basic problem with the accuracy of sundials is the Analemma. Due to the
> tilt of the Earth, the position of the shadow for a given time moves in a
> "figure-of-eight" shape over the course of the year. Therefore, even if the
> sundial is very accurately marked and positioned, the shadow will only fall
> exactly on the hour line twice a year - the winter and summer solstices.
>
> The figure-of eight Analemma is quite often marked for midday (and can
> serve to give the date as well). On large sundials, the Analemma may also
> be marked for every hour - but on a smaller dial, this can be visually very
> confusing! Another solution, used on heliochronometers, is to allow the
> dial to rotate against a scale marked with the appropriate Analemma offsets
> according to the date.
>
> Best wishes,
> Patrick
>
> On Tue, 30 Jul 2019 at 14:40,  wrote:
>
>> Hi Steve,
>>
>> as I built a large one (https://Kepleruhr.eu with 240m²) and thought some
>> about getting as accurate as possible here are my readings so far:
>>
>> 1) If you go for a sharp edge you will find out that the penumbra is all
>> the
>> times about 2 min in width which is the wandering time of all of the sun
>> diameter: The sun diameter is roughly 0.5° in the sky and it takes
>> roughly 2
>> min for the sun to move this angle. The penumbra in angle does not depend
>> on
>> the distance from the gnomon to the face. So I would suggest that the
>> reading would be +/-2 min for untrained and about +/-1 min for trained
>> observers. This is valid for sundials using the bypassing shadow of the
>> Gnomon or the moving flare of any rectangle or circular iris.
>>
>> 2) I estimate a reading accuracy of the Kepleruhr by +/-15 sec (at high
>> noon
>> only): There is a wandering flare of 2 cm (+/- penumbra) with two side
>> edges
>> on a line of 2 cm which increases the reading accuracy. This wandering
>> flare
>> is produced by a spherical Nodus with this 2 cm gap southwards. There are
>> some movies at the concerning YouTube-channel (links given at the
>> website).
>>
>> 3) In my case I made the calibration of the sundial by
>>a) calculate the hour and day line positioning by given parameters
>> (declination, geometry of gnomon, Nodus, wall)
>>b) erect the gnomon to the wall firstly without the painting
>>c) observe the shadow at one of the next fully sunny days - taking
>> series
>> of photos, calibrate them with respect to lens distortions, positioning,
>> etc
>>d) find the hourly shadow positions by machine vision techniques
>>e) adjust the above given parameter set as long as the total error of
>> deviations between the calculated and measured positions got a minimum
>>f) calculate the lines with the latest parameter set and do the
>> painting.
>>g) BINGO - it turned out (observing the sundial 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] Im Auftrag von Steve
>> Lelievre
>> Gesendet: Dienstag, 30. Juli 2019 19:38
>> An: Sundial List 
>> 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
>>
>>
>>
>> ---
>> 

Accurate sun dial

[Neville Michie]

Hi,
I am investigating a sun dial which it is claimed
will be accurate to a fraction of a minute.
It is based on the sundials made by Cooke, 
who was the New South Wales Government Astronomer
up to 1928.
The difficulties in making it are to make an analemma
with the days of the year marked on it. The device 
has a clock dial with hour hand and minute hand.
I have the facilities to make all the parts, the 
challenge is to make it the best of its kind.
The original model came in two versions,
a cheap version and a deluxe. There is still 
some reverse engineering to do to re-create 
the original designs which are only available
as pictures.
I am attaching a picture of the cheaper model.
Cheers, 
Neville Michie




---
https://lists.uni-koeln.de/mailman/listinfo/sundial

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

[Steve Lelievre]

Hi everyone,

Just to clarify ... my request is for information about the accuracy 
that any makers on this list /have actually achieved/.


Thanks, Kurt, for your answer for the KEPLERUHR dial. By the way, 
everyone, Kurt's dial is the subject of an article in the next issue of 
The North American Sundial Society's journal, The Compendium (September 
2019), coming soon.


Alexi, regarding an uneven wall, I'm designing for a plate mounted to a 
wall, not for a dial painted directly on the wall. Measurement errors 
for declination and inclination of the plate will affect operation but, 
yes, my plan relates to a planar surface (or pretty darn close!)


Patrick, regarding the analemma, I'm looking at doing a Local Solar Time 
dial, not a Mean Time dial, but I'll probably have an Equation of Time 
chart.


Best,
Steve





On 2019-07-30 12:40 p.m., kepler...@gmail.com wrote:


As I mentioned at my implementation approach I eventually did not take 
the parameters I got from maps or measurements by a ruler – I took the 
least square error approach by finally parameter adjustment and e.g. 
got to the news that the wall is horizontally 0.7° out of angle with 
respect to remote imaging/mapping.


Kurt

*Von:*Perit Alexei Pace [mailto:a...@onvol.net]
*Gesendet:* Dienstag, 30. Juli 2019 21:30
*An:* Patrick Vyvyan 
*Cc:* kepler...@gmail.com; Sundial List 
*Betreff:* Re: What accuracy to aim for with a carefully made sundial?

Another source of error apart from those mentioned in the original 
post is how accurate can a wall's declination be measured, say to half 
a degree. And what error would half a degree make depends on the size 
of your sundial. We are also assuming the wall is planar and built 
perfectly plumb!


Alexei

On Tue, 30 Jul 2019 at 21:16, Patrick Vyvyan > wrote:


A basic problem with the accuracy of sundials is the Analemma. Due
to the tilt of the Earth, the position of the shadow for a given
time moves in a "figure-of-eight" shape over the course of the
year. Therefore, even if the sundial is very accurately marked and
positioned, the shadow will only fall exactly on the hour line
twice a year - the winter and summer solstices.

The figure-of eight Analemma is quite often marked for midday (and
can serve to give the date as well). On large sundials, the
Analemma may also be marked for every hour - but on a smaller
dial, this can be visually very confusing! Another solution, used
on heliochronometers, is to allow the dial to rotate against a
scale marked with the appropriate Analemma offsets according to
the date.

Best wishes,

Patrick

On Tue, 30 Jul 2019 at 14:40, mailto:kepler...@gmail.com>> wrote:

Hi Steve,

as I built a large one (https://Kepleruhr.eu with 240m²) and
thought some
about getting as accurate as possible here are my readings so far:

1) If you go for a sharp edge you will find out that the
penumbra is all the
times about 2 min in width which is the wandering time of all
of the sun
diameter: The sun diameter is roughly 0.5° in the sky and it
takes roughly 2
min for the sun to move this angle. The penumbra in angle does
not depend on
the distance from the gnomon to the face. So I would suggest
that the
reading would be +/-2 min for untrained and about +/-1 min for
trained
observers. This is valid for sundials using the bypassing
shadow of the
Gnomon or the moving flare of any rectangle or circular iris.

2) I estimate a reading accuracy of the Kepleruhr by +/-15 sec
(at high noon
only): There is a wandering flare of 2 cm (+/- penumbra) with
two side edges
on a line of 2 cm which increases the reading accuracy. This
wandering flare
is produced by a spherical Nodus with this 2 cm gap
southwards. There are
some movies at the concerning YouTube-channel (links given at
the website).

3) In my case I made the calibration of the sundial by
   a) calculate the hour and day line positioning by given
parameters
(declination, geometry of gnomon, Nodus, wall)
   b) erect the gnomon to the wall firstly without the painting
   c) observe the shadow at one of the next fully sunny days -
taking series
of photos, calibrate them with respect to lens distortions,
positioning, etc
   d) find the hourly shadow positions by machine vision
techniques
   e) adjust the above given parameter set as long as the
total error of
deviations between the calculated and measured positions got a
minimum
   f) calculate the lines with the latest parameter set and do
the painting.
   g) BINGO - it turned out (observing the sundial since
years) 

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

[Perit Alexei Pace]

Another source of error apart from those mentioned in the original post is
how accurate can a wall's declination be measured, say to half a degree.
And what error would half a degree make depends on the size of your
sundial. We are also assuming the wall is planar and built perfectly plumb!

Alexei

On Tue, 30 Jul 2019 at 21:16, Patrick Vyvyan 
wrote:

> A basic problem with the accuracy of sundials is the Analemma. Due to the
> tilt of the Earth, the position of the shadow for a given time moves in a
> "figure-of-eight" shape over the course of the year. Therefore, even if the
> sundial is very accurately marked and positioned, the shadow will only fall
> exactly on the hour line twice a year - the winter and summer solstices.
>
> The figure-of eight Analemma is quite often marked for midday (and can
> serve to give the date as well). On large sundials, the Analemma may also
> be marked for every hour - but on a smaller dial, this can be visually very
> confusing! Another solution, used on heliochronometers, is to allow the
> dial to rotate against a scale marked with the appropriate Analemma offsets
> according to the date.
>
> Best wishes,
> Patrick
>
> On Tue, 30 Jul 2019 at 14:40,  wrote:
>
>> Hi Steve,
>>
>> as I built a large one (https://Kepleruhr.eu with 240m²) and thought some
>> about getting as accurate as possible here are my readings so far:
>>
>> 1) If you go for a sharp edge you will find out that the penumbra is all
>> the
>> times about 2 min in width which is the wandering time of all of the sun
>> diameter: The sun diameter is roughly 0.5° in the sky and it takes
>> roughly 2
>> min for the sun to move this angle. The penumbra in angle does not depend
>> on
>> the distance from the gnomon to the face. So I would suggest that the
>> reading would be +/-2 min for untrained and about +/-1 min for trained
>> observers. This is valid for sundials using the bypassing shadow of the
>> Gnomon or the moving flare of any rectangle or circular iris.
>>
>> 2) I estimate a reading accuracy of the Kepleruhr by +/-15 sec (at high
>> noon
>> only): There is a wandering flare of 2 cm (+/- penumbra) with two side
>> edges
>> on a line of 2 cm which increases the reading accuracy. This wandering
>> flare
>> is produced by a spherical Nodus with this 2 cm gap southwards. There are
>> some movies at the concerning YouTube-channel (links given at the
>> website).
>>
>> 3) In my case I made the calibration of the sundial by
>>a) calculate the hour and day line positioning by given parameters
>> (declination, geometry of gnomon, Nodus, wall)
>>b) erect the gnomon to the wall firstly without the painting
>>c) observe the shadow at one of the next fully sunny days - taking
>> series
>> of photos, calibrate them with respect to lens distortions, positioning,
>> etc
>>d) find the hourly shadow positions by machine vision techniques
>>e) adjust the above given parameter set as long as the total error of
>> deviations between the calculated and measured positions got a minimum
>>f) calculate the lines with the latest parameter set and do the
>> painting.
>>g) BINGO - it turned out (observing the sundial 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] Im Auftrag von Steve
>> Lelievre
>> Gesendet: Dienstag, 30. Juli 2019 19:38
>> An: Sundial List 
>> 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
>>
>>
>>
>> 

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

[Patrick Vyvyan]

 A basic problem with the accuracy of sundials is the Analemma. Due to the
tilt of the Earth, the position of the shadow for a given time moves in a
"figure-of-eight" shape over the course of the year. Therefore, even if the
sundial is very accurately marked and positioned, the shadow will only fall
exactly on the hour line twice a year - the winter and summer solstices.

The figure-of eight Analemma is quite often marked for midday (and can
serve to give the date as well). On large sundials, the Analemma may also
be marked for every hour - but on a smaller dial, this can be visually very
confusing! Another solution, used on heliochronometers, is to allow the
dial to rotate against a scale marked with the appropriate Analemma offsets
according to the date.

Best wishes,
Patrick

On Tue, 30 Jul 2019 at 14:40,  wrote:

> Hi Steve,
>
> as I built a large one (https://Kepleruhr.eu with 240m²) and thought some
> about getting as accurate as possible here are my readings so far:
>
> 1) If you go for a sharp edge you will find out that the penumbra is all
> the
> times about 2 min in width which is the wandering time of all of the sun
> diameter: The sun diameter is roughly 0.5° in the sky and it takes roughly
> 2
> min for the sun to move this angle. The penumbra in angle does not depend
> on
> the distance from the gnomon to the face. So I would suggest that the
> reading would be +/-2 min for untrained and about +/-1 min for trained
> observers. This is valid for sundials using the bypassing shadow of the
> Gnomon or the moving flare of any rectangle or circular iris.
>
> 2) I estimate a reading accuracy of the Kepleruhr by +/-15 sec (at high
> noon
> only): There is a wandering flare of 2 cm (+/- penumbra) with two side
> edges
> on a line of 2 cm which increases the reading accuracy. This wandering
> flare
> is produced by a spherical Nodus with this 2 cm gap southwards. There are
> some movies at the concerning YouTube-channel (links given at the website).
>
> 3) In my case I made the calibration of the sundial by
>a) calculate the hour and day line positioning by given parameters
> (declination, geometry of gnomon, Nodus, wall)
>b) erect the gnomon to the wall firstly without the painting
>c) observe the shadow at one of the next fully sunny days - taking
> series
> of photos, calibrate them with respect to lens distortions, positioning,
> etc
>d) find the hourly shadow positions by machine vision techniques
>e) adjust the above given parameter set as long as the total error of
> deviations between the calculated and measured positions got a minimum
>f) calculate the lines with the latest parameter set and do the
> painting.
>g) BINGO - it turned out (observing the sundial 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] Im Auftrag von Steve
> Lelievre
> Gesendet: Dienstag, 30. Juli 2019 19:38
> An: Sundial List 
> 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
>
>
>
> ---
> https://lists.uni-koeln.de/mailman/listinfo/sundial
>
>
> ---
> https://lists.uni-koeln.de/mailman/listinfo/sundial
>
>
---
https://lists.uni-koeln.de/mailman/listinfo/sundial

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

[kepleruhr]

Hi Steve,

as I built a large one (https://Kepleruhr.eu with 240m²) and thought some
about getting as accurate as possible here are my readings so far:

1) If you go for a sharp edge you will find out that the penumbra is all the
times about 2 min in width which is the wandering time of all of the sun
diameter: The sun diameter is roughly 0.5° in the sky and it takes roughly 2
min for the sun to move this angle. The penumbra in angle does not depend on
the distance from the gnomon to the face. So I would suggest that the
reading would be +/-2 min for untrained and about +/-1 min for trained
observers. This is valid for sundials using the bypassing shadow of the
Gnomon or the moving flare of any rectangle or circular iris.

2) I estimate a reading accuracy of the Kepleruhr by +/-15 sec (at high noon
only): There is a wandering flare of 2 cm (+/- penumbra) with two side edges
on a line of 2 cm which increases the reading accuracy. This wandering flare
is produced by a spherical Nodus with this 2 cm gap southwards. There are
some movies at the concerning YouTube-channel (links given at the website).

3) In my case I made the calibration of the sundial by
   a) calculate the hour and day line positioning by given parameters
(declination, geometry of gnomon, Nodus, wall)
   b) erect the gnomon to the wall firstly without the painting
   c) observe the shadow at one of the next fully sunny days - taking series
of photos, calibrate them with respect to lens distortions, positioning, etc
   d) find the hourly shadow positions by machine vision techniques
   e) adjust the above given parameter set as long as the total error of
deviations between the calculated and measured positions got a minimum
   f) calculate the lines with the latest parameter set and do the painting.
   g) BINGO - it turned out (observing the sundial 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] Im Auftrag von Steve
Lelievre
Gesendet: Dienstag, 30. Juli 2019 19:38
An: Sundial List 
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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---
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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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