NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: GHAA formula
From: Bill Murdoch
Date: 1997 Dec 07, 9:16 PM
From: Bill Murdoch
Date: 1997 Dec 07, 9:16 PM
Paul Hirose posted a shortened copy of the formula that I had given for the GHA of Aries. I do not disagree with shortening the formula at all. As you can guess, the exact formula has many more terms and longer constants than I gave. I cut it down to only include cyclic terms of 0.0000009 rev or 0.02' or larger, I left in the T^2 term, and I changed the time in the cyclic terms from ephemeris time to universal time. It should exactly match the Nautical Almanac perhaps 99% of the time. So far I have not found it off by more than 0.1' although it is possible that the sines in the terms I cut could gang up and all have a value of +1 or -1. But, as Paul says it is still really overkill for practical small boat celestial. What really puzzles me is why the formula (which is so simple) does not show up in navigation texts ? Why is it only in calculational astronomy texts ? Bill Murdoch Kingsport, TN =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=--=-= =-= TO UNSUBSCRIBE, send this message to majordomo@ronin.com: =-= =-= navigation =-= =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=--=-=
