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SAB

Ganymede sketch, Jupiter and Uranus Obs

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After having surgery on my toe, I thus had no work last night (Friday 19 Nov) so took advantage of the clear skies. 7timer predicted good seeing until midnight and skippy sky was showing 9/10 for the whole night.

Seeing was very good from after sunset until about 12:30-1am, when it deteriorated slightly.

Time: sunset-3am

Scope: 12" F/4.4 truss dob

Seeing: 7/10 dropping to 6/10

Transparency: 0/5 (nearly full moon)

Spent the first half of the night largely on Jupiter and Uranus.

Jupiter

At 267x, I caught the GRS just as it was dissappearing over the planet's eastern limb. The spot is pale and a light pinkish colour. The outer rim appeared slightly darker than the interior. As the evening progressed, seeing continued to improve, and at 334x at 10:52UT (9:52pm local DST) I could see some interesting features coming into view in the SEB. Three white ovals, with the preceeding one the largest and the following two decreasing in size were seen, along with a darkish cloud feature that appeared intertwined between the ovals. The most obvious part of this feature stretched between the large preceeding oval and the second oval, looping over the preceeding oval appearing similar to the classic side-on view drawing of a breaking wave.

Ganymede

Seeing was good enough to view the Galilean moons as disks, each with obvious difference in size. At 534x, in moments of good seeing, I caught some surface markings on Ganymede. In the northern hemisphere a dark wedge shaped feature could be seen, while the northern polar regions appeared lighter and whitish compared to the orange-yellow hue of the rest of the moon. Seeing was still blurring the image, but it also settled enough to get a crisp view of the disk momentarily. I also noted Ganymede's orange-yellow colour contrasting with Callisto's Ice-blue, which was a neat sight.

Uranus

Uranus was the clearest I've ever seen it, even at 534x, the disk was pretty crisp, and at 334x it was text-book perfect! On a typical night at 250x things start to go south. So, at 534x I got a nice pale blue ball, and despite moonlight, Titania was spotted. I attempted to see albedo features that some other observers had noted, and I suspected the polar region to be slightly lighter tone, but could not be certain.

Ganymede Sketch:

gmede.jpg

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amazing! In my scope the moons are just dots. I had no idea you could get visual detail on the moons with any scope, even 12". I'm surprised Ganymede is yellow/orange to your eyes - Io certainly is that color, but I thought Ganymede would be grey ice.

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Wow - they are that big with a 12-inch? Would I be likely to see anything good using a 10-inch at about 480X (5mm eyepiece with a 2X Barlow)? Also, what would be your chances of seeing a volcano eruption on Io?

Edited by george7378

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Well done SAB, fantastic observations. It's amazing what difference the seeing makes, it must have been pretty perfect to get x534 and with a near full moon.

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Crikey! very impressive by the sounds of things. i cannot wait for my first light.

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Thanks for your comments guys!

amazing! In my scope the moons are just dots. I had no idea you could get visual detail on the moons with any scope, even 12". I'm surprised Ganymede is yellow/orange to your eyes - Io certainly is that color, but I thought Ganymede would be grey ice.

Ganymede's true colour is actually a rusty golden-brown, it's Callisto that seems to have a subdued greyish colour. I got a nice contrast between the two as they were next to each other.

Wow - they are that big with a 12-inch? Would I be likely to see anything good using a 10-inch at about 480X (5mm eyepiece with a 2X Barlow)? Also, what would be your chances of seeing a volcano eruption on Io?

The disk is very small even at 534x but still clearly a disk. To put a perspective on it, it's about half the angular diameter of Uranus. A 10 inch at 480x could well pick up the dusky shading on Ganymede, but seeing has to be *dead steady*, otherwise the tiny disk just blurs and jumps around in the turbulance making observation impossible.

Also, what would be your chances of seeing a volcano eruption on Io?

That's not possible.

Well done SAB, fantastic observations. It's amazing what difference the seeing makes, it must have been pretty perfect to get x534 and with a near full moon.

Thanks Doc! Yep it was a rare night, also looked at other targets to gauge the seeing. Uranus was a nice crisp ball at 534x (as opposed to unresolved blurry blob) and 47 Tuc was incredibly crisp at 334x, even at 762x stars snapped thru focus rather than just mush through it. Jupiter itself was sharp at 334x, but dropped off once you got into the high 300's, he's not very tolerant of magnification!

Edited by SAB

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