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A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Tinyac almanac program for Windows
From: Paul Hirose
Date: 2010 May 13, 15:42 -0700
From: Paul Hirose
Date: 2010 May 13, 15:42 -0700
Dave Walden wrote: > lat seems to effect geocentric LHA? It shouldn't, and I haven't noticed that it does. For example, body = Sun, topocenter = Griffith Observatory (the default), time = 2010 May 13 2200 UT1 (delta T = 67.781 to match the USNO MICA program), coordinate reference system = apparent geocentric geodetic (LHA) of date. Tinyac says LHA = 32°37'08.8", lat = +18°31'46.4". Turning to MICA at the same time, GAST = 13 26 12.1065, true geocentric RA = 3 22 31.920. GHA = GAST - RA = 10 03 40.1865 (time) = 150 55 02.798 (arc). Subtract the longitude of the topocenter (118 17 54.0) to obtain 32 37 08.8. Declination = 18 31 46.45. These are identical to the Tinyac values. Now switch Tinyac to topocentric origin, leaving other settings unchanged. LHA = 32°37'12.7", lat = +18°31'43.8". In MICA, get the apparent topocentric RA and dec and repeat the steps above. Again, the match is perfect. (For this test I used the built-in SOFA ephemeris to show that it's impressively accurate in the present epoch for the Sun. It's equally good for the Earth. Other bodies are considerably less accurate, though.) By the way, an HTML message is not a reliable way to get my attention. (See my sig.) If there were any other replies, I missed them. I wasn't watching my Trash folder for filtered-out messages because I figured the user base for this program would be somewhere between negligible and nil. Besides, I do make it clear there's a filter. I'll try to pay more attention from now on, but there's a good deal of trash to look over each day, and I don't do it very carefully. I've never been one to fret about missing a few messages. That casual attitude includes my own postings. If one failed to show up (which I don't think has happened here yet) I probably wouldn't bother to repost or make an inquiry. --