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    Re: Nautical Almanacs
    From: Stan K
    Date: 2015 May 26, 22:28 -0400
    A quick look indicates to me that these tables, practically speaking, are as good as any.  In some areas they attempt to be better than the Nautical Almanac.  For instance, these tables give v and d values for the planets for each day of the three days on a page, rather than giving one value for all three days.

    My question is, what is their standard of accuracy?  Quite a few values are a bit off of the Nautical Almanac values, some of which we know are deliberately "misadjusted".  For instance, take the GHA of the Sun for 17h UT on 1 January 2015.  These tables agree with most sources, including the USNO web site, with a value of 74º07.2'.  However, the Nautical Almanac, which adjusts the GHA of the Sun to allow for the fact that it does not provide v values, gives a value of 74º07.0'.  Strictly speaking, the former value is more accurate, but if you are taking a Power Squadrons exam you had better use the latter value.

    (FWIW, Celestial Tools has two modes for the Sun.  In the "Nautical Almanac" mode it gives 74º07.0'.  In the "Accurate" mode it gives 74º07.2'.  Unadjusted (accurate) values for the hourly GHA of the Sun are in disagreement with the Nautical Almanac about 50% of the 8760 hours in a (non-leap) year by as much as 0.2'.  In the "Nautical Almanac" mode Celestial Tools agrees with the Nautical Almanac for almost 99% of the hours, and never disagrees by more than 0.1'.)

    Stan


    -----Original Message-----
    From: Henry Halboth <NoReply_Halboth@fer3.com>
    To: slk1000 <slk1000@aol.com>
    Sent: Tue, May 26, 2015 9:27 pm
    Subject: [NavList] Nautical Almanacs

    To all,

    I recently stumbled acoss a website claiming to provide astronomical data to an accuracy of 0.3'. I have not as yet had the opportunity to check this claim out, however, the tables do look somewhat impressive. Is anyone familiar with this site?


    Henry
       
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