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 Post subject: solar ephemeris
PostPosted: Thu Aug 10, 2006 1:20 am 
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Joined: Thu Aug 10, 2006 1:15 am
Posts: 2
I need a web site or software (Windows XP and Windows 2000) to calculate the position of the sun. The entries should include latitude and longitude to tenth of a second, time to the second, and altitude. The utility is to produce the azimuth and elevation to the center of the sun to an accuracy of 0.1 degrees and better if possible. The simpler the better.

I found a web site that does this but it gives the answer in right asc and declination. I don’t know how to convert to azimuth and elevation. If I cannot find a program to calculate the az and el directly utility to do this conversion would be nice.

Thanks for your time,
Bkelly
b1 at bkelly dot ws


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PostPosted: Thu Aug 10, 2006 7:58 am 
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Joined: Fri Dec 03, 2004 2:41 pm
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Location: 55° 57'N: 03° 08'W
You will probably find something suitable here:

http://websurf.nao.rl.ac.uk/surfbin/first.cgi

:)


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PostPosted: Thu Aug 10, 2006 11:49 am 
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Joined: Thu Aug 10, 2006 1:15 am
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Thats a nice simple site, but the accuracy is not sufficient. I need to enter lat and long to tenths of a second and time to the second and I need azimuth and elevation to at least 0.1 degrees, preferably 0.01.

Thanks for taking the time to respond.
Bkelly


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PostPosted: Sun Aug 13, 2006 1:01 pm 
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Joined: Sun Aug 13, 2006 12:29 pm
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Location: Goosnargh, north of Preston, UK
Hi bkelly,

When discussing high-accuracy calulation of solar coordinates, Jean Meuus - in his book 'Astronomical Alorithms', says the following...

"A very high accuracy, better than 0.01 arcsecond, is obtained when use is made of the complete VSOP87 theory (see chapter 32), but for the Earth this theory contains 2425 periodic terms..."

I'd certainly recommend the book, if you want to tackle the calculation yourself. If not, then a search for VSOP87 (or Variations Séculaires des Orbites Planétaires 87) throws up several hits, but generally for computer applications or software modules. However, Wikipedia suggests that Celestia implements the VSOP87 theory, so downloading that could possibly answer your question. Unfortunately, I've not used Celestia myself and don't know for sure it does what you want.

http://www.shatters.net/celestia/

Something to watch out for is the effect of atmospheric refraction on the apparent position of the Sun. You'll need to know if you want it included in your calculation, or not.

Lots to think about.

javascript:emoticon(':?')
Confused


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