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    New JPL long ephemeris
    From: Paul Hirose
    Date: 2011 Jul 18, 13:15 -0700

    Ephemeris or almanac programmers may be interested to know the Jet 
    Propulsion Laboratory put their latest "long ephemeris" online a few 
    months ago. DE422 covers 3000 BC to 3000 AD, the same as DE406. The 
    binary files are about 3 times larger for the same time span, though.
    
    All JPL ephemerides online are described here:
    http://ssd.jpl.nasa.gov/?planet_eph_export
    
    And the files are at this FTP site:
    ftp://ssd.jpl.nasa.gov/pub/eph/planets/
    
    Note that the ephemerides are just data files. You must supply the
    software to extract the positions of the solar system bodies. In 
    addition, Windows users must download the ephemerides in ASCII form and 
    convert them to binary.
    
    The free astronomy DLL I distribute requires a trick to use a DE422 
    ephemeris. (This is also true for my Tinyac program, which depends on 
    the DLL.) The DLL uses the filetype (.422) to look up the file's "record 
    length" in an internal table. But the latest ephemerides are not yet in 
    the table. Fortunately, DE421 has the same record length, and it is in 
    the table. So, if you give a DE422 ephemeris a .421 filename it works 
    perfectly. This is explained on the Web page 
    (http://home.earthlink.net/~s543t-24dst/sofajplNet/index.html)
    
    How does DE422 compare to DE406, the old long ephemeris? I tested 11 
    geocentric positions at 3-day intervals in November 283 BC. The total 
    (great circle) discrepancy in the Moon's position was .0038° to .0050° 
    (13" to 18").
    
    Why that year and month? Because last December in the History of 
    Astronomy mailing list we had a discussion about a possible Spica 
    occultation in November 283 BC. Of course there was some argument about 
    the accuracy of modern ephemerides at such a remote epoch.
    
    The messages are archived at 
    http://listserv.wvu.edu/cgi-bin/wa?A0=hastro-l, but you must be a list 
    member to access the archive. If you would like to see the specifics of 
    the "occultation", without joining HASTRO-L, they're also in a Journal 
    of Cosmology article by Anton R. Peters, 2010, Vol 9, 2245-2258:
    http://journalofcosmology.com/AncientAstronomy123.html (part 4)
    
    By the way, the occultation proponent eventually admitted there was no 
    occultation, only a close conjunction. His precession calculation had 
    been wrong.
    
    -- 
    I filter out messages with attachments or HTML.
    
    
    
    
    

       
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