Jupiter - not a shadow transit last night?

[kerrylewis]

Postings here refer to shadow transit last night around 20.00 but apps etc show it as a moon - Callisto. These usually look bright against the planet and can be difficult to see but last night's transit was dark and looked just like a shadow. At first I thought that the shadow and the moon might be coinciding but this seems to be impossible.

Anyone have the definitive answer - moon or shadow?

[Stu]

Jupiter Moons lists a multiple moon transit, but there is only Callisto showing so I assume it must have been a shadow too. I saw a shadow very clearly last night, and know from experience that I can't see the moons themselves once they are away from the limb, there is not enough contrast with a small scope.

Still looking for a 'definitive answer' though.....

Stu

[kerrylewis]

Yes Stu - I had the same. I assumed that 'multiple moon transit' might mean moon + shadow but I could only see what looked like a shadow in the position that the app was predicting the moon to be.

I have seen moons in transit but agree that they are not easy to see until they get near the limb, and look bright not dark.

Someone out there must have the answer!

[Stu]

Kerry, this site lists all transit and occultation events for the moons and does not list a shadow transit for that time..... Intriguing!

http://www.projectpluto.com/jevent.htm

Stu

[Stu]

Some discussion here about Galilean moon appearance...

http://www.cloudynights.com/ubbthreads/showflat.php/Number/4040244

[kerrylewis]

It is intriguing. It seems like we did see a moon and not a shadow. Any images? There is one in the beginners section but that looks likes shadow. And why did the app list a 'multiple' transit? I will not rest until we have the definitive!!

[Stu]

Yes, was trying to understand whether Callisto is darker than the others and so would show up better. Not convinced yet though.....

[U Cyg]

Here is a link to an image that shows how dark Callisto is against the face of Jupiter.  The image in the third post shows Callisto along with the shadow of Ganymede.

http://tinyurl.com/qcul9mk

[Stu]

Fabulous U Cyg, that seems to explain it. It proves that I've never seen Callisto transiting before because I've not been able to pick up the other moons except near the limb. I'm amazed it was so clear, could have sworn it was a shadow.

Many thanks,

Stu

[lukebl]

I was watching this too and was surprised how dark it was. Although it looked like a shadow, it was actually Callisto itself which is very dark. Just goes to show how bright Jupiter is compared to its moon. Jupiter has an albedo of over 0.5, whereas Callisto is only 0.2, hence it appears dark in comparison.

[Stu]

Thanks Lukebl, any ideas why it was shown as a multiple transit in Jupiter Moons?

[JB80]

Well I guess that is what I saw too then, it certainly was very distinct.

[kyokugaisha]

I was also very surprised by how dark it looked. I took the image below but the seeing wasn't really good enough to show it as anything other than a black circle - just how it looked to the eye.

However WinJupos shows the scene very clearly.

[kerrylewis]

Great responses. So, that's it then- it wasn't a shadow but Callisto itself. It was amazingly dark and distinct and I will now look out for further transits by this moon. Anyone know when the next one is?

[JB80]

And definitely post a heads up the day before and maybe people can be prepared for imaging it.

[Stu]

Kerry, have a look in the link I posted earlier, projectpluto. This has a list for the whole year. They are not so frequent because Callisto is the outermost moon and so takes longest to orbit.

Looks like the next one is on 28th March but early in the morning (effectively very late night 27th :-) ) 3.12am until 6.46am

Callisto is IV in this list

Stu

[kerrylewis]

Great. You really do learn something every day in this hobby and on this forum. I have seen moon transits before but never looking like this. It makes you want to turn back the clock 24 hrs and watch again but hopefully we will see more images or videos. Meanwhile I've set the alarm for 3.12 on March 28th!

[lukebl]

?.... Meanwhile I've set the alarm for 3.12 on March 28th!

Don't bother. Jupiter will have set by then!

[kerrylewis]

Don't bother. Jupiter will have set by then!

Really? Didn't think of that! I'll be there in spirit anyway. And there'll always be another time

[lukebl]

Really? Didn't think of that! ....

Easily done. I often plan to view or image something and then suddenly realise that it has set, or the sun had risen, or the full moon is in the way, or it's hidden by my big apple tree, or all sorts of other reasons!

[Stu]

Don't bother. Jupiter will have set by then!

DOH!!

Didn't even think of that, assumed it would still be visible. Will look further......

[kerrylewis]

Jupiter has been around for so long now I tend to think that it's a permanent fixture! But we have Saturn and Mars to look forward to as replacements.

[Stu]

Take two!

How about 13th April? Coincides with GRS Transit too, starting around 10.30 at 36 degrees altitude.

Stu

[kerrylewis]

Take two!

How about 13th April? Coincides with GRS Transit too, starting around 10.30 at 36 degrees altitude.

Stu

Looks good . I don't have a great view to the west from the garden but with judicious positioning of the scope I should get it. BUT it will be cloudy.........

[Stu]

Think positive Kerry, think positive!! This cloud must end sometime!