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A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Almanac data
From: Peter Hakel
Date: 2009 Jun 7, 16:03 -0700
From: "frankreed@HistoricalAtlas.com" <frankreed@HistoricalAtlas.com>
To: NavList@fer3.com
Sent: Thursday, June 4, 2009 11:40:58 PM
Subject: [NavList 8514] Re: Almanac data
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
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From: Peter Hakel
Date: 2009 Jun 7, 16:03 -0700
A demo of this spreadsheet can be viewed at:
http://www.youtube.com/watch?v=CyHVqqVJQH0
The spreadsheet itself can be freely downloaded at:
http://www.navigation-spreadsheets.com/uploads/moon.xls
Analytic expressions for DeltaT are available at:
http://eclipse.gsfc.nasa.gov/SEhelp/deltatpoly2004.html
Peter Hakel
http://www.youtube.com/watch?v=CyHVqqVJQH0
The spreadsheet itself can be freely downloaded at:
http://www.navigation-spreadsheets.com/uploads/moon.xls
Analytic expressions for DeltaT are available at:
http://eclipse.gsfc.nasa.gov/SEhelp/deltatpoly2004.html
Peter Hakel
From: "frankreed@HistoricalAtlas.com" <frankreed@HistoricalAtlas.com>
To: NavList@fer3.com
Sent: Thursday, June 4, 2009 11:40:58 PM
Subject: [NavList 8514] Re: Almanac data
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
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