NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Almanac data
From: Frank Reed
Date: 2009 Jun 4, 23:40 -0700
From: Frank Reed
Date: 2009 Jun 4, 23:40 -0700
Last week, I wrote regarding Peter Hakel's Moon spreadsheet: "I tried out some dates and noticed that the Moon's position is right on the money for 2009, but it's a few tenths of a minute of arc off c.1950 and a couple of minutes of arc out if I go back two centuries. Those are fairly big error for lunars. It appears that you're using a simple expression for delta-T that's quadratic in time." Peter sent me a revised version to preview with expanded delta-T calculations, and his numbers now agree with with the almanac data from my software to within two or three seconds of arc of difference at most, usually less. We've used entirely different approaches to generate the ephemerides, so the agreement is not due to identical implementation of the algorithms or any other "lucky accident". -FER --~--~---------~--~----~------------~-------~--~----~ Navigation List archive: www.fer3.com/arc To post, email NavList@fer3.com To , email NavList-@fer3.com -~----------~----~----~----~------~----~------~--~---