# Buying an Electronic Sundial. **URL:** \ **Category:** Factual Questions\ **Created:** [December 2, 2007, 3:01am UTC](https://boards.straightdope.com/t/buying-an-electronic-sundial/428516 "2007-12-02T03:01:46Z")\ **Posts on this page:** 7\ **Page:** 1
**Author:** ![Jim\_B](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jim_b/32/4338_2.png) [@Jim\_B](https://boards.straightdope.com/u/Jim_B)\ **Post date:** [December 2, 2007, 3:01am UTC](https://boards.straightdope.com/t/buying-an-electronic-sundial/428516/1 "2007-12-02T03:01:46Z")
For a couple of years now, I have been thinking about buying a sundial. As many of you probably already know, sundial time follows the apparent course of the sun, which is neither Standard nor Daylight time, except by coincidence. The only problem with buying a sundial time is setting it at first. I know almanacs can help with this. But I also wonder if there are any electronic gadgets that can show sundial time. Quite frankly, sundials are such a run-around (what with the problems of reading them on overcast days, etc.) I may just get the electronic gadget and forget about the sundial altogether. Does anyone know where they sell something, if anything, like this? And what do they call this electronic appliance, if it exists? 🙂 ---
**Author:** ![Inner\_Stickler](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/inner_stickler/32/318_2.png) [@Inner\_Stickler](https://boards.straightdope.com/u/Inner_Stickler)\ **Post date:** [December 2, 2007, 3:05am UTC](https://boards.straightdope.com/t/buying-an-electronic-sundial/428516/2 "2007-12-02T03:05:26Z")
A watch? (Have I been whooshed?) ---
**Author:** ![Jim\_B](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jim_b/32/4338_2.png) [@Jim\_B](https://boards.straightdope.com/u/Jim_B)\ **Post date:** [December 2, 2007, 3:10am UTC](https://boards.straightdope.com/t/buying-an-electronic-sundial/428516/3 "2007-12-02T03:10:48Z")
[QUOTE=Inner Stickler] A watch? (Have I been whooshed?) [/QUOTE] I assume you’re joking 🙂 . But just to take your post seriously for future posters, as I have already pointed out, Standard and Daylight time are **not** Sundial time, except by coincidence. Both time systems work on an entirely different principal. Standard/Daylight time follow the **average** time it takes the sun to evolve around the planet in a year. If you tried to set a regular watch to solar time, it would always be a little too fast, or a little too slow. I don’t fully understand it myself. But getting an almanac over the years has educated me a little 🙂 . ---
**Author:** ![Inner\_Stickler](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/inner_stickler/32/318_2.png) [@Inner\_Stickler](https://boards.straightdope.com/u/Inner_Stickler)\ **Post date:** [December 2, 2007, 3:15am UTC](https://boards.straightdope.com/t/buying-an-electronic-sundial/428516/4 "2007-12-02T03:15:03Z")
What a curious thing. _Toddles off to Wikipedia_ ---
**Author:** ![LSLGuy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lslguy/32/5813_2.png) [@LSLGuy](https://boards.straightdope.com/u/LSLGuy)\ **Post date:** [December 2, 2007, 3:19am UTC](https://boards.straightdope.com/t/buying-an-electronic-sundial/428516/5 "2007-12-02T03:19:28Z")
IANA astronomer nor horologist, but I expect the USNO web site, or that of Astronomy magazine can help. Determining the correct solar time for your lat/long is mathematically trivial, so they probably have a calulator page to do that. Once you know the clock time that corresponds to local solar noon at your location on a given day, you can set your sundial so it reads noon at that clock time & you’re almost in business. You’ll need to correct for the difference between local solar noon today and local noon on the equinox. But that’s easy: just get the clock time for local noon on the equinox date & compare it to today’s time. 5 minutes later? Add 5 minutes to the today noon clock time when setting your sundial & you’re done. A Google for “mean solar time” calculator will probably set you up. ---
**Author:** ![Napier](https://avatars.discourse-cdn.com/v4/letter/n/ce73a5/32.png) [@Napier](https://boards.straightdope.com/u/Napier)\ **Post date:** [December 2, 2007, 11:22am UTC](https://boards.straightdope.com/t/buying-an-electronic-sundial/428516/6 "2007-12-02T11:22:01Z")
A fancy sundial can have an analemma built in so it does read a version of time that is correct year around. You will have to aim the sundial not straight up, but at the zenith for the middle of your time zone. You can just use the analemma on a globe, too. Maybe you are looking for a calculator for the position of the sun (and other major objects) at an arbitrary time. I have used [http://aa.usno.navy.mil/data/docs/topocentric.php](http://aa.usno.navy.mil/data/docs/topocentric.php) and it is handy and easy. ---
**Author:** ![rowrrbazzle](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/rowrrbazzle/32/414_2.png) [@rowrrbazzle](https://boards.straightdope.com/u/rowrrbazzle)\ **Post date:** [December 3, 2007, 1:31am UTC](https://boards.straightdope.com/t/buying-an-electronic-sundial/428516/7 "2007-12-03T01:31:50Z")
[QUOTE=LSLGuy] You’ll need to correct for the difference between local solar noon today and local noon on the **equinox**. But that’s easy: just get the clock time for local noon on the **equinox** date & compare it to today’s time. 5 minutes later? Add 5 minutes to the today noon clock time when setting your sundial & you’re done. [/QUOTE] According to Wikipedia, the difference is zero about 3 weeks from the equinoxes, and only a few days from the solstices. > **[Equation of time | Secular effects](https://en.wikipedia.org/wiki/Equation_of_time#Secular_effects)** > > (Note: the word “secular” in this context means “pertaining to the passage of time over long periods”, not “lacking religion”. See, for example, “secular trend”, which also uses the word in this sense.) > The two above mentioned factors have different wavelengths, amplitudes and phases, so their combined contribution is an irregular wave. At epoch 2000 these are the values (in minutes and seconds with UT dates):