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