sunlit-design.com is back online! (Apologies - corrected URL)

[David Pratten]

Dear 
Dialists,
 
After a period of 
hibernation, http://www.sunlit-design.com is 
back online - to stay!
 
Today, I have 
uploaded a unique dynamic suntime - clock time visualisation that may be of 
interest to dialists. http://www.sunlit-design.com/gallery/visualisations/eot1.php 
  Some of you will remember the first visualisation that I produced a 
few years ago.  Today I have updated so that it is different every day of 
the year (depending on EOT values) and also can be used to interactively explore 
the annual variations in EOT.
 
Your feedback on the 
visualisation is welcome.
 
As well - The Sun 
API (high accuracy solar calculation software) is now totally free for 
commerical and personal use!
 
All the 
best
 
David
---
https://lists.uni-koeln.de/mailman/listinfo/sundial

sunlit-design.com is back online!

[David Pratten]

Dear 
Dialists,
 
After a period of 
hibernation, http://www.sunlit-design.com is 
back online - to stay!
 
Today, I have 
uploaded a unique dynamic suntime - clock time visualisation that may be of 
interest to dialists. http://localthesunapi.com/gallery/visualisations/eot1.php Some 
of you will remember the first visualisation that I produced a few years 
ago.  Today I have updated so that it is different every day of the year 
(depending on EOT values) and also can be used to interactively explore the 
annual variations in EOT.
 
Your feedback on the 
visualisation is welcome.
 
As well - The Sun 
API (high accuracy solar calculation software) is now totally free for 
commerical and personal use!
 
All the 
best
 
David
---
https://lists.uni-koeln.de/mailman/listinfo/sundial

Curiosity Dept: Ice sundial

[David Pratten]

Title: Message



Dear 
All,
 
Yesterday I was 
looking at the nice sharp shadow of an ice scupture about 3 foot high and I 
realised that it would be possible to make a sundial out of ice!  Does 
anyone know if this has been done and are there any photos on the 
web?
 
Thanks
David

Analemma Photos article at Wired.com

[David Pratten]

Title: Message



Dear 
All,
 
Thought you may like 
this ... http://www.wired.com/news/technology/0,1282,65428,00.html
 
David
 
For sun related 
calculation needs ... visit http://www.sunlitdesign.com/products/thesunapi/

RE: Precise EOT Program - Correction

[David Pratten]

Hello Gianni, Fer and John,

Yes you are correct.  December 22-23.  I had another look at my spreadsheet
and found that I had misread it.  

All the best

David

> -Original Message-
> From: [EMAIL PROTECTED] 
> [mailto:[EMAIL PROTECTED] On Behalf Of Gianni Ferrari
> Sent: Saturday, 14 June 2003 9:20 PM
> To: sundial@rrz.uni-koeln.de
> Subject: Re: Precise EOT Program
> 
> 
> 
> Hello John,
> 
> also I  have found  the values given by Fer.
> 
> The maximum change of the EOT , between the local noons  of 
> two consecutive days, is,  in 2003,  equal to  29.98 secs  - 
> 22/23 December.
> 
> Within December 20 and 25,  the changes are around constant  
> and equal to 29.90 - 29.98 sec
> 
> In 2004 (leap year) the maximum of the EOT change occurs  
> between  21 and 22 December, and it is equal to 29.8 sec
> 
> A regard
> 
> Gianni Ferrari
> 
> 44° 39' N  10° 55' E
> Mailto : [EMAIL PROTECTED]
> 
> 
> 
> 
> -
> 
> 


-

RE: Precise EOT Program

[David Pratten]

Dear John,

The Sun API is a software component that will do all EOT/ Declination plus a
lot of conversion between units etc.
www.sunlitdesign.com/products/thesunapi 

The program works in degrees (which is convenient for mortals) and
implements Meeus's algorithms.  The program is accurate to within 250ms for
EOT (compared to MICA/ ICE).

The program also has routines which will find the time of solstices and
equinoxes.

The program works in two modes.  One is the MJD (Modified Julian Day based
on UT) and the other  is perfect for building real sundials.  The second
time base (SDY) gives for any time of any day of the year - an average value
for EOT/ Declination for the next century.

For John's purposes, the ability of the program to work with Excel is a real
bonus.  A table of eot values for every 10 seconds during an observation
period can easily be generated.

Check it out.

The author

David Pratten
Sunlit Design





> -Original Message-
> From: [EMAIL PROTECTED] 
> [mailto:[EMAIL PROTECTED] On Behalf Of John Carmichael
> Sent: Friday, 13 June 2003 4:14 AM
> To: Sundial List
> Subject: Precise EOT Program
> 
> 
> Hello all,
> 
> I'm looking for a handy precise program that calculates EOT values in 
> minutes and seconds at particular times during the day. In other 
> words, I don't want the average EOT value for the day as found in the 
> printed tabular EOT values in Mayall & Waugh.  Instead, it would give 
> the exact EOT value at a particular time during the day.
> 
> I've found several EOT calculator programs (applets) on the "Current 
> Data" link at sundials.org. Does anybody know if the values given in 
> these applets are daily averages or precise values?
> 
> Thanks for any suggestions.
> 
> John
> 
> John L. Carmichael Jr.
> Sundial Sculptures
> 925 E. Foothills Dr.
> Tucson Arizona 85718
> USA
> 
> Tel: 520-696-1709
> Email: [EMAIL PROTECTED]
> Website: <http://www.sundialsculptures.com>
> 
> 
> -
> 
> 


-

RE: Precise EOT Program

[David Pratten]

Dear John,

Courtesy of The Sun API and Excel.

December 26th/ 27th

The greatest difference is .12333 degrees or 29.60 seconds.

David


> -Original Message-
> From: [EMAIL PROTECTED]
> [mailto:[EMAIL PROTECTED] On Behalf Of John Carmichael
> Sent: Friday, 13 June 2003 8:17 PM
> To: sundial@rrz.uni-koeln.de
> Subject: Re: Precise EOT Program
> 
> 
> Hi everybody,
> 
> Thanks to all who wrote. Looks like most people favor the
> Dialist Companion for precise EOT values.
> 
> I need precise EOT for setting my sundials and for precise
> time readings. I got spoiled at Kitt Peak by Bob Hough's 
> complete list of these EOT values. I can see definite shadow 
> movement in as little as 10 seconds on my large cable dials 
> and I know that EOT values can change more than that in just 
> one day.  By the way, does anybody know what the maximum 
> amount EOT changes in 24 hours and on what date this occurs?
> 
> John
> 
> John L. Carmichael Jr.
> Sundial Sculptures
> 925 E. Foothills Dr.
> Tucson Arizona 85718
> USA
> 
> Tel: 520-696-1709
> Email: [EMAIL PROTECTED]
> Website: 
> - Original Message -
> From: "fer j. de vries" <[EMAIL PROTECTED]>
> To: 
> Sent: Friday, June 13, 2003 1:22 AM
> Subject: Re: Precise EOT Program
> 
> 
> > John,
> >
> > Even if you want a procedure to calculate the EoT at a
> certain time at
> > a certain day, what accuracy do you need? If 5 seconds is
> enough you
> > could use the year formula calculated by my program equadecl. Use as 
> > input a decimal daynumber to get the wanted EoT but
> also correct
> for
> > the longitude you are living.
> > The basic output is for noon GMT.
> >
> > If you need higher precision then look for another procedure.
> >
> > I also would like to know for what reason you need such a
> procedure in
> > dialing.
> >
> > Fer.
> >
> >
> > Fer J. de Vries
> >
> > De Zonnewijzerkring
> > mailto:[EMAIL PROTECTED]
> > http://www.de-zonnewijzerkring.nl
> >
> > Home
> > mailto:[EMAIL PROTECTED] http://www.iae.nl/users/ferdv/index-fer.htm
> > Eindhoven, Netherlands
> > lat.  51:30 N  long.  5:30 E
> >
> > - Original Message -
> > From: "John Carmichael" <[EMAIL PROTECTED]>
> > To: "Sundial List" 
> > Sent: Thursday, June 12, 2003 11:14 PM
> > Subject: Precise EOT Program
> >
> >
> > > Hello all,
> > >
> > > I'm looking for a handy precise program that calculates
> EOT values
> > > in minutes and seconds at particular times during the
> day. In other
> > > words,
> I
> > > don't want the average EOT value for the day as found in
> the printed
> > tabular
> > > EOT values in Mayall & Waugh.  Instead, it would give the
> exact EOT
> value
> > at
> > > a particular time during the day.
> > >
> > > I've found several EOT calculator programs (applets) on
> the "Current
> Data"
> > > link at sundials.org. Does anybody know if the values
> given in these
> > applets
> > > are daily averages or precise values?
> > >
> > > Thanks for any suggestions.
> > >
> > > John
> > >
> > > John L. Carmichael Jr.
> > > Sundial Sculptures
> > > 925 E. Foothills Dr.
> > > Tucson Arizona 85718
> > > USA
> > >
> > > Tel: 520-696-1709
> > > Email: [EMAIL PROTECTED]
> > > Website: 
> > >
> > >
> > > -
> > >
> >
> > -
> >
> 
> 
> -
> 
> 

-

RE: Re equation of time

[David Pratten]

Title: Message



Dear 
Doug,
 
The 
factors that make the sundial 'fast' or 'slow' are not dependent on 
latitude.  
 
See http://www.sunlitdesign.com/infosearch/equationoftime.htm and 

 
http://www.sunlitdesign.com/products/thesunapi/documentation/sdxEOT.htm for 
a function to calculate the Equation of Time  If you note the parameters to 
this function you will see that latitude is not necessary for calculating 
it.
 
David

  
  -Original Message-From: 
  [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On 
  Behalf Of dougdotSent: Wednesday, 16 October 2002 7:26 
  AMTo: sundial@rrz.uni-koeln.deSubject: Re equation of 
  time
  Hello all,
  As a newcomer to dialling, I would like to know 
  whether the "fast" or "slow" as shown on the graph is the same for the 
  southern hemisphere as for the northern hemisphere.
  Doug

RE: seeking for an azimuth software

[David Pratten]

Dear Alain,

Check out www.sunlitdesign.com/products/thesunapi

David

-Original Message-
From: [EMAIL PROTECTED]
[mailto:[EMAIL PROTECTED] On Behalf Of Alain MORY
Sent: Saturday, 14 September 2002 3:51 AM
To: sundial@rrz.uni-koeln.de
Subject: seeking for an azimuth software


Hello !

I'm searching for a soft that could be able to give the date and the
azimuth of the sun, when a time is given. I made picture of engraved
neolithic stones, at some precise times and I wanted to know if they
could point one or more 
famous times in the year.
Does anybody knows such a soft ?

Alain MORY
47°57N
6°57E




-



-

Sundial Enthusiasts in Australia

[David Pratten]

Dear All,

While I normally live in Kazakhstan, I am currently in Australia.  I
would love to hear (off list) from anyone in Australia with an interest
in Sundials.  You can email me at mailto:[EMAIL PROTECTED] or phone me
in Sydney (02) 9585 2565

Thanks

David Pratten
www.sunlitdesign.com


-Original Message-
From: [EMAIL PROTECTED]
[mailto:[EMAIL PROTECTED] On Behalf Of Richard Mallett
Sent: Wednesday, 6 March 2002 9:13 AM
To: [EMAIL PROTECTED]
Subject: Re: Reflector Reply Change


Reply to : Larry McDavid

>>  Why did we want this change? <<

I'm glad of it (although I did not request it) because with my email
software (NAVCIS) I can only reply to the originating address.  All the
other mailing lists that I belong to (such as the ones on yahoo groups)
use the list address as the originating address, and I have never seen
any objections to this method.  If I want to send a personal email to
the sender (which for me is comparatively rare) I just look for 'From: '
in the message header.

Richard.


  E-mail from: Richard Mallett, 04-Mar-2002
-

-

RE: On northern vs. southern dials

[David Pratten]

Title: Message



Dear 
All,
 
I 
concede - the same answer by logic (Fer) and by brute 
force(Mark).
 
David
 
-Original Message-From: 
[EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On 
Behalf Of fer j. de vriesSent: Monday, 4 March 2002 9:05 
AMTo: sundialSubject: Re: On northern vs. southern 
dials

  Anselmo et All,
   
  I think the answer to your question is latitude 
  45 degrees.
   
  At any place the sun is half a year above the 
  horizon.
  This also means that the sum of the hours that a 
  north facing wall and a south facing wall catch the sun also is half a 
  year.
   
  So we have to look for the latitude where a north 
  facing dial catches the smallest amount of the sun ( or where a south facing 
  dial gets the highest amount of the sun ).
   
  At the pole the sun shines at the north side for 
  50% as you said.
  Going to lower latitudes this percentage 
  decreases to a minimum but than increases to the same amount of 
  50% again at the equator as you also said.
   
  At first glance I should answer that minimum than 
  will be just between at latitude 45 degrees.
   
  If this symmetry is true this also would mean 
  that at latitude X and at latitude 90 - X the number of hours of sunshine on a 
  north facing dial is equal. ( and the numbers of hours of sunshine on the 
  south dial also is equal )
   
  And indeed this is true.
   
  Have a look at the attached pictures of a north 
  facing dial at 23.5 and at 66.5 degrees.
  You may see that the amount of sunshine is equal 
  for both latitudes.
  And this equality is present for any couple of 
  latitude X and 90 -X.
   
  So I think that the answer to your question 
  is 45 degrees.
   
  Best wishes, Fer.
   
  Fer J. de Vries[EMAIL PROTECTED]http://www.iae.nl/users/ferdv/Eindhoven, 
  Netherlandslat.  51:30 N  long.  
  5:30 E
  
- Original Message - 
From: 
Anselmo Pérez 
Serrada 
To: Sundial, Mailinglist 
Sent: Sunday, March 03, 2002 5:02 
PM
Subject: Re: On northern vs. southern 
dials

Hi Mike, hi diallists,
 
   When I said a sundial in the North 
Pole I meant a sundial, say, at 1 cm from it. There the
concept of North still makes sense and it is 
obvious that there there are as many hours of
sunlight in the northern side than in the 
southern side in the course of a year. And we can
make the same reasoning for a dial in the 
Equator: there we have the same result, but with
a different distribution along the 
days.
 
As for the 'not-50%+50%' question, you may 
look at two things to realize that it is not like this
in all latitudes:
   1st Take a glance at the lines in 
a classical azimuthal sundial (you can make one with Sonne 
program).
   2nd (and more convincing ;) just 
ask how much does it cost a flat or a house oriented southwards
and another one oriented northwards... Where I 
live the difference is no less than 3 euros!
 
I do believe (David Pratten said something like 
this) that the bigger differences occur close to the the
Arctic Circles and to the Tropical Circles, but 
I can't prove it. I suppose that in the end I'll have to apply brute 

force but I think as well there must be a 
better way to prove it.
 
Anselmo

  - Original Message - 
  From: 
  The 
  Shaws 
  To: sundial@rrz.uni-koeln.de 
  Sent: Sunday, March 03, 2002 1:54 
  PM
  Subject: RE: On northern vs. southern 
  dials
  
  Thinking about this question a little more - during the course of a 
  complete year, doesn't every point on Earth get 50% light and 50% 
  dark?
  So, the further North (or South) you go, the more of the 50% shines 
  on the South (or North) facing wall.
  So the North (or South) pole is the place to go to get the 
  maximum light shining on the South (or North) facing 
  wall.
   
  
  Mike Shawhttp://homepage.ntlworld.com/jmikeshaw/N 53º 21' 
  24"W 03º 01' 47"Wirral, UK. 
 

RE: On northern vs. southern dials

[David Pratten]

Title: Message



Dear 
All,
 
I will 
take an intuitive punt on any point on the arctic circle as having maximum 
ratio of southern exposure to northern exposure.  Can't prove 
it.
David

  
  -Original Message-From: 
  [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On 
  Behalf Of Anselmo Pérez SerradaSent: Sunday, 3 March 2002 9:27 
  AMTo: Sundial, MailinglistSubject: On northern vs. 
  southern dials
  Hi everyone,
   
     Imagine an oriented wall (gnomonic 
  declination equals to 0 deg in one side and 180 deg in the other), all of us 
  know that the
  southern side is exposed more time to sunlight 
  than the northern one, but where is this difference bigger?  It is 
  clear that in the 
  equator and in the North Pole the rate is 50% to 50%, ie., both sides receive the 
  same amount of sunlight through a whole year, 
  so there must be 
  in the middle some latitude where the difference becomes maximal. 
  Which is that latitude?
   
     OK, I know we can solve it easily by 
  'brute force' but is there a simpler method to determine that value? I didn't 
  find it.
   
     Now that I remember, a kind of 
  touristical question: in this month's issue of the spanish version of 
  Scientific American there is an article
  by D. Savoie about sundials an in it he says that 
  in the Place de la Concorde in Paris it was drawn a sundial (an Oughtred 
  sundial
  I suppose) based on the obelisk erected there. 
  Does anybody know if the lines are still drawn or were they 
  erased?
   
   
  Anselmo Perez Serrada
   
   
  PS: My apologizes for Southern diallists (you all 
  know about our Northern egoccentrism!). Just swap the words North and 
  South.

RE: Polar ceiling sundial

[David Pratten]

The BSS sundial glossary has the following entry under "Types of Dials":

"reflecting ~: these dials have no gnomon, but reflect sunlight by means
of a semi-cylindrical mirror, set with the axis of the mirror parallel
to the polar axis. The mirror reflects the light to form a caustic curve
amongst the hour points. For the special case of the mirror having a
cycloid shape, the hour points are equally spaced. Note that the term
reflecting dial may also be used for ceiling dials."

What is the typical dialface for a 'reflecting dial'?  Are the comments
above about semi-cylindrical mirrors apply equally to ceiling and wall
dials?

If a polar ceiling dial has an inclination of phi/2 what does having a
mirror inclined at phi do?

What is a caustic curve?

David

Refraction

[David Pratten]

Title: Message



 
 
Dear 
Dialists,
 
I have been 
pondering the effect of refraction on dial performance.
 
Refraction quoted at 
.1 degree to .5 degree apparent difference in altitude below 10 degrees of 
altitude, will impact the hour angle to some degree.  See http://www.gcstudio.com/calcuse.html These 
are average values - refraction (according to Meeus quoting someone) can vary by 
up to .3 degree at the lower altitudes.
 
1. It would seem to me that dials 
that attempt to tell time during the hour after sunrise and hour 
before sunset could usefully take refraction into account.  However 
altitude for a given hour angle changes through out the year.  
Are there dials laid out with reference to average refraction 
effects?
 
And
 
2. We know that Mean 
time + EoT = Apparent Time 
 
However because 
viewing the sun through our atmosphere's refraction is unavoidable - 
Is there 
established terminology to distinguish between Apparent Time (geometric) as 
just defined above and Actual Observable Apparent Time (after 
refraction)?
 
David
 
 

Did it pass unnoticed?

[David Pratten]

Title: Message



Dear 
Dialists,
 
Merry Christmas - 
and did it pass us unnoticed?  Today at 2001/12/25 05:32:02 [UT] our dials 
and our watches are running in synchronisation!
 
David
www.sunlitdesign.com 
 
 

RE: accuracy

[David Pratten]

Dear Walter,

Greetings.  

There is another factor which limits sundial accuracy to about +/-22
seconds.  This is the variation in the value of Equation of Time from
year to year within a leap cycle.  See
www.sunlitdesign.com/infosearch/sundialaccuracy.htm

David
www.sunlitdesign.com

-Original Message-
From: [EMAIL PROTECTED]
[mailto:[EMAIL PROTECTED] On Behalf Of walter.jonckheere
Sent: Thursday, 20 December 2001 8:47 PM
To: sundial@rrz.uni-koeln.de
Subject: accuracy


Greetings to all
We all know that the atomic clock has the highest possible resolution,
while for sundials 2 to 1 minute seems to be the best achievement. I
have a feeling 1 second could be obtained considering what follows. ( I
consider a second ideal as one can feel it, I mean it is a timespan well
related to the human body, one second you live, the next you may be
dead; it is also somewhat related to the heartbeat) Consider a
horizontal sundial whith the 15 degrees hour lines; it is impossible to
trace minute lines when keeping usual dimensions for the dial. However,
if we go far away from the base point of the gnomon, the portion of the
arc between 2 hours, becomes larger; so imagine we go to where 60 lines
can be drawn between two adjacent minute lines and we keep only the top
part of the line 11h59m59s and try to draw it on the ground related to a
very accurate positioning of the local meridian. These data allow also
to calculate the height of the gnomon tip. If both dimensions are
feasable to realise, we would have the desired accuracy of one second;
of course the positioning of the meridian is of paramount importance and
probably the most difficult to materialise. ( is this a nice subject for
a university ?) Of some important influence is the width of  the gnomon.
The indication of noon time is never accurate because of this width,
while the shadow cast for the earlier hours, may be considered as a
hairline and is thus more accurate, which means that the morning part of
the dial is more accurate if the shadow hairline is taken into account
for determination of the meridian. So in fact, sundials should have a
gap at noon corresponding to the width of the gnomon, and the afternoon
part should be calculated in function of the right hairline shadow
related to a second parallel meridian. Very interested to read your
comments Walter

RE: Query about solstices

[David Pratten]

Dear Fritz,

Using Find Annual Feature function (sdxFindAnnFeatx)of the The SUN API
www.sunlitdesign.com/products/thesunapi I get the follwing value for the
solstice this December:

December 21 19:21:30.7143 [UT] (which is +/- 10 seconds of the true
value)

Compare with   http://aa.usno.navy.mil/data/docs/EarthSeasons.html which
shows the value to the nearest minute.

Using the Declination function (sdxDecl) we find the declination for
this time on the 20th, 21st and 22nd:

20th -23:26:06.7694
21st -23:26:20.9605 SOLSTICE
22nd -23:26:06.8546

Which have the following differences from the Solstice

20th -0:00:14.1911
21st 0  SOLSTICE
22nd -0:00:14.1060


David
www.sunlitdesign.com

-Original Message-
From: [EMAIL PROTECTED]
[mailto:[EMAIL PROTECTED] On Behalf Of Fritz Stumpges
Sent: Thursday, 20 December 2001 9:12 AM
To: 'Frank Evans'; sundial@rrz.uni-koeln.de
Subject: RE: Query about solstices


This topic got me wanting to get a piece of pipe and try it!
>From my new Sky software, which I'm just getting to know,
I found that solstice is at about 11:22 on the 21st.  I
then got the declinations on the day before and after at this time.  But
the sun changes only 14 seconds(arc)/day.  This means that on the 20th
it is -23deg26m14s and on the solstice it is -23deg26m28s.  How does
this compare with other sources for accuracy?

Anyway, at this required resolution, it would take a "pipe"
or earthen hole, 307 feet long, assuming a "pinhole" or? which could be
resolved as 1/4 of an inch of movement (@307 ft!) This is to measure the
actual movement that day with respect to the day before and day after.
Is this correct?  And if so, I doubt they really could resolve this.
This is 130 times smaller than the apparent diameter of the sun!?

What do you all think?  There goes the fun I was going to have with this
endeavor tomorrow.  I'll be there celebrating this magical moment
anyway, as I'm sure many of you will

Cheers,

Fritz 

-Original Message-
From: Frank Evans [mailto:[EMAIL PROTECTED]
Sent: Wednesday, December 19, 2001 11:46 AM
To: sundial@rrz.uni-koeln.de
Subject: Query about solstices


Greetings fellow dialists,

You don't have to have a clear sky on the actual day you are wishing to
mark sunrise or sunset. Martin Brennan in his book "The Stones of Time"
showed elegantly how the people at Newgrange in Ireland did it five
thousand years ago with the rising solsticial sun shining down a long
shaft into the immense earthwork onto auxiliary marks for adjacent days.

More recently there is a simple noon line in Durham Cathedral dated 1829
with extra marks for five and ten minutes after noon. This line was
simply a clock regulator, though.

Frank, 55N 1W
-- 
Frank Evans

RE: Sundial link

[David Pratten]

Mounting the sundial upside down so that the face is oriented as for
Britian will make the hour numbers go the right way ...

David

-Original Message-
From: [EMAIL PROTECTED]
[mailto:[EMAIL PROTECTED] On Behalf Of The Shaws
Sent: Wednesday, 12 December 2001 10:06 PM
To: [EMAIL PROTECTED]; sundial@rrz.uni-koeln.de
Subject: RE: Sundial link


 I note that on the link it says:-

<>

Perhaps the slight snag that the hour numbers go round the opposite way
might have been worth mentioning

Mike Shaw

http://homepage.ntlworld.com/jmikeshaw/

N 53º 21' 24"
W 03º 01' 47"
Wirral, UK.



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