-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 Here's a link which might shed at least a little light on some differences in the computational models: http://www.centerforspace.com/downloads/files/pubs/AIAA%202006-6753%20Revisiting%20Spacetrack%20Report%203.pdf I received the above from a friendly lurker on the list. It was quite enlightening, and made me understand some of the historical issues with things like picking the right epoch and time system to base the calculations on. It's 88 pages, but the layout puts some of the most interesting pieces in the first six pages. There's also the subject of the specific mathematical libraries used. Not representing a number properly and accounting for "roundoff error" can result in really bogus predictions. I confronted this myself in the past, and if I hadn't been writing programs to work on both a Palm Pilot and my Linux systems, I would not have noticed the 30-arc-minute-or-so discrepancies in star positions. This was for celestial navigation, so such a huge error was intolerable to me. Regarding Heavensat, Mike McCants wrote: > There are no RA and Dec labels on this display. This is confusing. Maybe a note to the authors? Anyone with energy to write and release such a tool would probably desire it to be "right." Or so I'd hope. :) John -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.2.2 (MingW32) Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org iD8DBQFFRq7FEd1YUJfL25YRAqCvAJ9jMONaeu21cbQKzGidh8D00tzf1ACgp3Iz bYp0QLPCakufLbg8q4vJdEo= =ioCC -----END PGP SIGNATURE----- ------------------------------------------------------------------------- Subscribe/Unsubscribe info, Frequently Asked Questions, SeeSat-L archive: http://www.satobs.org/seesat/seesatindex.html
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