Jupiter GRS plus double moon and shadow transit

[Stu]

Early start for that one Dave!

[Stu]

Rob, I can't quite remember which is the smallest scope I have seen the moons in transit, probably the 4". It is very difficult, if not impossible unless they are near the limb, where the limb darkening gives them more contrast.

One of the moons has a much lower albedo, possibly Callisto and appears almost like a shadow when it is in transit, much easier to see than the others.

[Qualia]

That's brilliant information, Stu. I had no idea Callisto's albedo or even how to go about seeing actual moon transits, so what you've written will be a lot of help. I guess it is possible just not that easy to do. 

[Stu]

I only discovered the info about Callisto by accident Rob. I was observing what I thought was a shadow transit but the Jupiter Moons App listed it as a moon transit. I thought there was a mistake, but then saw it appear after transiting.

I hope this link works, I found an excellent video on YouTube showing how dark it is when in transit.

Because it is the moon which orbits furthest from Jupiter, its orbit is around 16 days so transits at convenient times are far less frequent than the other moons.

Coming back to the limb darkening, I do find that if you watch the moon enter transit you can follow it relatively easily whilst over the darker limb, then it gets progressively harder, often impossible until it reaches the other limb. Occasionally they are over a belt so the contrast is a little better. Callisto can be easily tracked all the way across though.

[Stu]

Just been running through SkySafari to track down the next good transit. There is one on 7th Jan but Jupiter is only just rising. There is a nice conjunction of thre of the moons though later on, at 3.52am on 8th; worth checking out.

The best Callisto transit seems to be February 9th, starting at around 8pm and ending at 1.45am ish.

The added fun is that there is a shadow transit too, plus A GRS transit. Some images to give times below:

[Qualia]

Wow! That is amazing information, Stu and thank you for putting this together. Amazing stuff I never thought such a thing would be possible, but following your advice, the next time I see Callisto ready to move across Jupiter at an hour I can observe, I'm going to give it a try. I won't be able to do 7^th for I work until 22:00, but thank you so much for seeking out that information. As the weeks go by, Jupiter is getting more and more interesting, just a shame that the GRS doesn't seem to putting on such a show as it has done in other years. Looking forward to the morning of the 24^th. If clouds play game, should be a great display   

Cheers again, Stu