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Re: GHA = GAST - RA Astronomical Almanac vs Nautical Almanac
From: Stan K
Date: 2014 Mar 22, 20:34 -0400
From: Stan K
Date: 2014 Mar 22, 20:34 -0400
Mike,
In addition to Delta T that Paul already mentioned, you have to consider the fact that the Sun is not a good one for comparison. The Nautical Almanac "fudges" the value of the GHA of the Sun because it ignores the v correction. Check page 261, paragraph 24 of the Almanac. Also check the NavList archive for some discussion of this.
Stan
In addition to Delta T that Paul already mentioned, you have to consider the fact that the Sun is not a good one for comparison. The Nautical Almanac "fudges" the value of the GHA of the Sun because it ignores the v correction. Check page 261, paragraph 24 of the Almanac. Also check the NavList archive for some discussion of this.
Stan
-----Original Message-----
From: Mike Mayer <mwmayer@tds.net>
To: slk1000 <slk1000@aol.com>
Sent: Sat, Mar 22, 2014 3:32 pm
Subject: [NavList] GHA = GAST - RA Astronomical Almanac vs Nautical Almanac
From: Mike Mayer <mwmayer@tds.net>
To: slk1000 <slk1000@aol.com>
Sent: Sat, Mar 22, 2014 3:32 pm
Subject: [NavList] GHA = GAST - RA Astronomical Almanac vs Nautical Almanac
Hi,
Anyone know what I'm missing? In comparing the Sun's GAST - RA from the Astronomical Almanac to the GHA in the Nautical Almanac there are cases that seem to be too far off. For example, for January 1, 2014 at 0 UT I get:
GAST = 6h42m17.0580s = 6.704738333h (Page B13)
RA = 18h45m35.31s = 18.759808333h (Page C6)
RA = 18h45m35.31s = 18.759808333h (Page C6)
GAST - RA = -12.055070000 = 11.944930000h = 179.17395° = 179°10'26.22"
= 179°10.437'
= 179°10.437'
The Nautical Almanac has 179°10.2'
The difference is 0.237', which is outside the accuracy the Nautical Almanac specifies for the GHA Sun data in the paragraph numbered 24 on page 261 of the commercial version of the Nautical Almanac 2014.
What am I missing ?
Thanks!
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