Celestia Forums

Hi Celestians!
Last night I was investigating on an uncommon event that will happen on 2008, May 25th, when Jupiter will not have any Galilean Satellite visible!
From 3:50:59 UT to 4:09:31 UT Jupiter's satellites will have the following positions:
- Europa is in transit in front of Jupiter
- Ganymede is covered (occulted) by the planet disk
- Callisto will be in Jupiter's shadow (eclipsed)
- Io will enter Jupiter's shadow (eclipsed)
So, during that short time lapse no Galilean satellite will be visible!

I tried to recreate this event with Celestia, just starting from my home (Rome, Italy) and looking at Jupiter and its satellites. Then for Io entering into umbra I made 4 snaphots, you can see here

http://wm51.inbox.com/thumbs/f4_e50ee_d9fa18c8_tn.jpg.thumb

http://wm51.inbox.com/thumbs/f5_e50ed_91aa3548_tn.jpg.thumb

http://wm51.inbox.com/thumbs/f6_e50ec_73eea2cc_tn.jpg.thumb

http://wm51.inbox.com/thumbs/f7_e50eb_2b9ebf4c_tn.jpg.thumb

The problem with these pictures is the shape of Jupiter's shadow on Io during the eclipse: it's concave instead of being convex!
Please think about our Moon, when it enters the Earth's shadow during an eclipse and you'll convince yourself that the shadow on Io is completely wrong!

Chris, what do you think about this bug?

Thanks a lot
Pierluigi

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Point size range: 1.000000 - 64.000000

piellepi wrote:The problem with these pictures is the shape of Jupiter's shadow on Io during the eclipse: it's concave instead of being convex!
Please think about our Moon, when it enters the Earth's shadow during an eclipse and you'll convince yourself that the shadow on Io is completely wrong!

Chris, what do you think about this bug?

I think that it is not a bug at all.

Jupiter is much larger with respect to Io than the Earth is with respect to the moon, so you can expect to see different shadows cast: the edge of Earth's shadow will be noticeably round, where as Jupiter's shadow is so large that the edge will look almost straight. The slight concavity is probably the result of the fact that the limb of Io is darker the center.

--Chris

I'm pretty sure your observations are due to the angle that you're viewing Io at, and the curvature of Io itself. Try going to Jupiter and looking at the Eclipse.



As you can see, it is properly rounded, convex.