a Sun Dial poser... where on Earth does it work?

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carson

carson

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  I have this neat little sundial that I brought back from the Texas Coast. 10 bucks from a roadside stand.

  Now, it does not show the correct time at my latitude... 28.9? North.

The angle of the indicator is about 52?. Without me doing all the hard work, can someone tell me at what latitude it would be accurate?

  I know it doesn't work on a rainy day  ;D  but I'll bet someone knows how to figure it out..Hurry, it's sunny today.  ;)

carson FL


 

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Well.. You did answer your own question (you said it shows the correct time at YOUR lattitude)

The answer is kind of complex.  A sun dial needs to be properly adjusted for where you are.. Ideally I'd have an elevation setting on the vane.  Then you could go out at "high noon" (Which may not actually be 12:00) and set it for "No shadow" (Shadow falls upon the vane itself) and go back oh say 3 hours later and set the height so it shows 3pm.

However even then it's not that easy
 
Hey John, here is what I said:

Now, it does not show the correct time at my latitude... 28.9? North.
Click to expand...

What say now?  At the wrong latitude there will be nothing linear/accurate about any sun dial.

carson
 
Must have missed the NOT.. Each sun dial, as I said,has to be designed for where it is sitting.

Thus any one that you buy, already made works as designed.. It is designed as a decoratoin.
 
You can learn a lot in general about sundials at  http://en.wikipedia.org/wiki/Sundial

and more about sun angles and latitude at

http://home.netcom.com/~abraxas2/sun.htm

Frankly, it's more than I ever wanted to know...
 
Great link, Gary.  "Since the style is aligned with the Earth's rotational axis, the style points true North and its angle with the horizontal equals the sundial's geographical latitude λ. A sundial designed for one latitude can be used in another latitude, provided that the sundial is tilted upwards or downwards by an angle equal to the difference in latitude. For example, a sundial designed for a latitude of 40? can be used at a latitude of 45?, if the sundial plane is tilted upwards by 5?, thus aligning the style with the Earth's rotational axis."  Seems like a fairly straightforward adjustment. 

If you try it, Carson, let us know how well or poorly it works out.  Cheers.  ...  Steve
 
Thanks Gary and Steve,

  Halfway reading through the links provided I got a headache. Think I'll go sit outside in the Sunshine until the symptoms disappear.  ;D


  I'll experiment with the tilting process, Steve. Makes sense, but first I have to finish reading. May even have to go back to College to take another math course.  ::)

  Darn it, it just clouded over; what'll I do now?

This subject sure keeps your mind of black water tanks !

  carson FL  (chuckling)

 
Eureka, I got it !!!

  The angle of the GNOMON, The angular part, is supposed to be equal to the Latitude of your location.

Ok, my angle is about 60? so it will work at the Southern Border of the Canadian Yukon Territories. I am sitting at 28.9? here in Florida. so I'll have to tilt it about 31.1?.... ok....

  I temporarily held it at that angle, making sure the Gnomon was pointing true North.

Just then it got cloudy again, drat... but I did notice before that it was hard to read the minutes and seconds on the shadow line, so I made a quick decision. I looked at my digital watch on my arm to get the right time and decided to scrap my Sun Dial project then and there.

  I want to thank you all for the tremendous help. Hope I also put a chuckle on your face.  8)

carson FL... have a sunny day

 
For the cloudy days you meed a solar operated sundial with the battery storage. 

OK, new product.  Indoor sundial, will work in day or night.  Has a gear driven halogen lamp that tracks as the sun does.  Great Brookstone item, or Sky Mall item.  Totally silly.  On fact I would also incorporate a projection clock to cast the digital time on the ceiling.  $349.05 plus shipping and handling.

 
Methinks you are on to something, Bill.

  I would add a GPS receiver so that it would automatically be accurate at any Latitude and Longitude anywhere in the World. Because of the great appeal it would sell worldwide, no doubt. Gotta think ahead.  ;D

  An idea like yours could be called "timeless".

  Just think, an IPO could make us rich.  ::)

carson FL

 
Let's build an electronic sun dial for outdoor use which is powered by solar panels. It follows the sun and shows the time. Had that idea a few years ago but never realized it...
 
Right on, Mike.

   If the unit had a quartz movement, updated by WWV in Colorado/WWVH in Hawaii (US Time Standard) by radio waves, add a digital readout and the problem would be solved. Just think what a revolutionary concept that would be.  ;)

  We should get going on that right away. Wunderbar! 

carson FL  60.0F  -  15.6C  cold here

 
carson,
no quartz movement, no radio waves, no digital readout. Just solar panels for the power supply, a monocular telescope, a scale - and a little trick to get the solar time.
 
Sorry for delay.

These are my "painted thoughts" for an electronic sun dial. Some description is given in the drawing. More information: The difference between the light sensitive sensors in both eyes (brightness respective voltage) is electronically compared. This results of the comparison results in driving a step motor or a servo motor which turns the figure around.

In the morning the brightness awakes the system via the solar panels.
The continuous comparison of the brightness in both eyes delvers the continuous actual direction to the sun.

The sunbeams enter the telescope on the one end. They leave the telescope at the other end and strikes the scale at the correct ?solar time?.
 

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Now we are talking, Mike... brilliant.  I want one.  ;)

  If it is fully automatic, can it find the Sun in the East every morning? Or maybe you have to aim it manually first. Quick, spend a few thousand Euros to patent it.  ;D

  carson FL
 
Carson, you don't need to aim manually. Because of the comparsion of the brightness (voltage) in the both eyes the system always searches the angle, where the brightness (voltage) is the same in both eyes. And that's the direction to the sun.
In bad weather it may not find the sun's position. So the system should fall asleep automatically in that case and tries again later. But in bad weather a "normal" sun dial doesn't work too...
 
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