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A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Nautical Almanac
From: Stan K
Date: 2016 Jul 19, 12:45 -0400
From: Stan K
Date: 2016 Jul 19, 12:45 -0400
Bob,
Thanks for sending this. I'll be taking a closer look at the Pyalmanac software just for the fun (?) of it.
So we have two versions of Enno's almanac available on the web, one dated December 1, 2014, the other dated November 9, 2015. Though I would tend to trust the later one more than the earlier one, another difference is that the earlier one has a section of celestial navigation formulas that the later one does not.
About the 60' instead of 0' issue, certainly worth fixing, but I think it is unlikely that even an "unsuspecting" navigator would not realize that -22º60.0' is the same as -23º00.0'.
Another couple of things in Enno's almanac that differ from the printed Nautical Almanac:
1) An occasional difference of 0.1' in the value of d for the Moon
2) The SD of the Moon is given once in Enno's almanac, but is given for each of the three days on a page in the printed Almanac, and the single value in Enno's almanac does not always correspond to that of the middle day of the printed Almanac.
There may be more differences, but, like these, they are probably insignificant, at least for real-life position finding. However, no on-line almanac I have ever seen is exactly like the printed Almanac, so they could not be used for, say, a Power Squadrons exam.
Stan
-----Original Message-----
From: Robert Pearson <NoReply_Pearson@fer3.com>
To: slk1000 <slk1000@aol.com>
Sent: Tue, Jul 19, 2016 10:24 am
Subject: [NavList] Re: Nautical Almanac
From: Robert Pearson <NoReply_Pearson@fer3.com>
To: slk1000 <slk1000@aol.com>
Sent: Tue, Jul 19, 2016 10:24 am
Subject: [NavList] Re: Nautical Almanac
Stan,
When I saw the Dec 1, 2014 date on the 1st page I thought this version (linked to in your post) would have the rounding error that give positive values for angle that are actually negative angles and have a 0 degree as the whole degree part. This error was corrected in an update to the Pyalmanac software package last Sept 2015. However I see this copy apparently was printed using the corrected software even though the creation date is clearly prior the the date of the fix.
Copies of the almanac and the python software package used to create it are available on Enno Rodegerdts' web site:
When I was playing around with the Python code last year I noticed 2 rounding errors in the code. When I went back to his website I found he had already posted an updated to the Pyalmanac package.
The other rounding error I found apparently hasn't been corrected and can be found both in the version you linked to and the current version on Enno's website. This error results in rounding to 60.+ minuites instead of 0.+. Not all that drastic but in a quick lookup an unsuspecting navigator might be pick a value 1 deg off. 1st error like this occurrs on pg 3 for sun's dec at 1800 on Fri Jan 01 2016.
Regards,
Bob Pearson
