Jupiter's moons changing appearance during transit

[tom_rs]

Hi all

On Sunday night while watching the transit of Ganymede from Perth, WA, I noticed that Ganymede had a dark, almost black appearance during the first half of its transit and during the last part had changed to a white appearance. There were quite a few clouds that night so I didn't see the white appearance until Ganymede was quite close to the end of its transit.

I've never watched a transit before so my apologies if this is a well known thing. But what might cause this change in appearance? Is it an optical illusion? Or a mistaken observation!

The shadow transit (+ that of Europa) was also quite visible and separate and I'm pretty sure I wasn't mistaking the two.

I had a look around on the internet for a similar description and found this article from 1867. But no others!

http://books.google.com.au/books?id=...QccKYr4I&hl=en

Cheers

Tom

[AlexN]

I think you'll find that this is caused when the moon exits the planets shadow... its the only plausible explanation I can think of...

Someone else with more knowledge of the topic will surely come and answer this more accurately.

Hope i've helped Tom,

Alex.

[iceman (Mike)]

Hi Tom, to IceInSpace!

Depending on the angle of the sun, I guess it could be possible. The galilean moons are locked in 1:1 tidal rotation with Jupiter so I guess it's possible that as it rotated as it orbited, it could've started reflecting more sunlight.

I'll have to pay more attention next Ganymede transit and see for myself?