I was using Celestia to investigate mutual events of Saturn's satellites (e.g. one moon casting a shadow on another) when I encountered a bug in Celestia. "Eclipses" (these events are properly called transits) in which the occulting body appears smaller than the sun are not correctly depicted in Celestia. These shadows generally appear too dark and have edges that are too crisp. I created a patch for Celestia that fixes these problems and gives much more realistic impressions of inter-moon eclipses. Here's a comparison of the shadow cast by Enceladus on Titan as it transits the Sun on 25 Jul 2009:
From Titan, Enceladus appears significantly smaller than the Sun. It doesn't block all of the Sun's light, thus the shadow in the first image is unrealistically dark.
Saturn's major satellites have orbits that lie close to its equatorial plane. Because Saturn is tilted significantly (almost 27 degrees) from its orbital plane, eclipses between satellites can only occur during a span of time near the planets equinoxes, which occur about every 15 years. The next equinox happens in 2009; hopefully, we'll see some nice images of eclipses from Cassini.
If you want to explore mutual events in the Saturnian system, you can get the patch here:
http://www.celestiaproject.net/~claurel/celest ... ipse.patch
This page has cel URLs for a few interesting events:
http://www.celestiaproject.net/~claurel/celest ... tests.html
And this table gives a comprehensive listing of mutual events during Saturn's 2009 equinox:
ftp://cdsarc.u-strasbg.fr/pub/cats/J/A+ ... tab4-7.dat
(Also so the ReadMe: ftp://cdsarc.u-strasbg.fr/pub/cats/J/A+A/485/293/ReadMe )
Discussion forum for Celestia developers; topics may only be started by members of the developers group, but anyone can post replies.
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