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Re: The Online Nautical Almanac
From: Frank Reed CT
Date: 2004 Jul 19, 23:12 EDT
From: Frank Reed CT
Date: 2004 Jul 19, 23:12 EDT
I wrote earlier:
>if you wanted the positions of the stars, for a historical lunars analysis
>maybe, in 1804, which would you recommend: Omar Reis's Online Nautical
>Almanac (as modified), or Centennia Software's Online Nautical Almanac?
George H replied:
"I really couldn't say. I haven't investigated Centennia Software's Online Nautical Almanac."
Sorry, George. I didn't mean to be obscure.
(Centennia Software) = (HistoricalAtlas.com) = (me).
In any case, let's take a specific example. For June 22, 1821, the position of Pollux is
SHA = 246d 24.6'
Dec = N28d 27.1'
according to my Online Nautical Almanac.
According to Omar Reis's Online Nautical Almanac (even after recent modifications), the position is
SHA = 246d 23.9'
Dec = N28d 28.2'.
The distance between those two positions is about 1.3 minutes of arc --not a big deal for standard celestial navigation but a very large error if one were using this position as an input for a lunars calculation. Many other stars have similarly large errors in their positions.
As I said earlier, the LARGEST problem with O.R.'s star positions arose because he failed to include proper motions. However, the positions are by no means correct yet. I can see at least two independent issues at work in his star positions, but I don't have time to puzzle out the source of these errors (this time around).
Centennia Software's Online Nautical Almanac is accessible here:
http://www.HistoricalAtlas.com/lunars
So far, my online almanac data tables and predicted lunars have passed every test I've thrown at them. They are accurate to a fraction of a second of arc in star positions and 1 second of arc (largest allowed error) in the positions of the Sun, Moon, and planets.
Since I began keeping count on July 7, my Online Almanac & Predicted Lunars tools have been used 412 times. Everybody please let me know if you encounter any problems. I am working on yet another set of enhancements and hope to have them available soon.
Frank R
[ ] Mystic, Connecticut
[X] Chicago, Illinois
>if you wanted the positions of the stars, for a historical lunars analysis
>maybe, in 1804, which would you recommend: Omar Reis's Online Nautical
>Almanac (as modified), or Centennia Software's Online Nautical Almanac?
George H replied:
"I really couldn't say. I haven't investigated Centennia Software's Online Nautical Almanac."
Sorry, George. I didn't mean to be obscure.
(Centennia Software) = (HistoricalAtlas.com) = (me).
In any case, let's take a specific example. For June 22, 1821, the position of Pollux is
SHA = 246d 24.6'
Dec = N28d 27.1'
according to my Online Nautical Almanac.
According to Omar Reis's Online Nautical Almanac (even after recent modifications), the position is
SHA = 246d 23.9'
Dec = N28d 28.2'.
The distance between those two positions is about 1.3 minutes of arc --not a big deal for standard celestial navigation but a very large error if one were using this position as an input for a lunars calculation. Many other stars have similarly large errors in their positions.
As I said earlier, the LARGEST problem with O.R.'s star positions arose because he failed to include proper motions. However, the positions are by no means correct yet. I can see at least two independent issues at work in his star positions, but I don't have time to puzzle out the source of these errors (this time around).
Centennia Software's Online Nautical Almanac is accessible here:
http://www.HistoricalAtlas.com/lunars
So far, my online almanac data tables and predicted lunars have passed every test I've thrown at them. They are accurate to a fraction of a second of arc in star positions and 1 second of arc (largest allowed error) in the positions of the Sun, Moon, and planets.
Since I began keeping count on July 7, my Online Almanac & Predicted Lunars tools have been used 412 times. Everybody please let me know if you encounter any problems. I am working on yet another set of enhancements and hope to have them available soon.
Frank R
[ ] Mystic, Connecticut
[X] Chicago, Illinois
