Friday, July 20, 2018

fun even in poor seeing

Seeing was very poor last night but I did have an interesting observation: Jupiter’s Galelean moons were in an unusual configuration.  They were all to the eastern side, and arranged in an offset / widely-spread trapezium.  Actually the pair closest to the planet was, at 9:30pm, about equidistant from the planet, while the outer pair was staggered.  I don’t recall ever seeing them all on one side.  I used the apodizing mask and was able to see some better detail, like the barges in the NEB and the still turbulent festoons.  No GRS.

I spent some time on the moon, but the seeing was so wavy, like looking at the bottom of a pool, that I began to feel slightly nauseous.  I did however locate the Apollo 11 landing site, including craters Armstrong, Collins, and Aldrin – so that’s a first.

Back to Jupiter, and this time (around 10:00) the northern moon of the nearer pair had moved outward, and the outer pair had moved closer together.  I watched for 20 minutes more, but the moons didn’t seem to move – I think they had reached the edges of their orbit and were travelling away from us, so still moving but the movement not perceptible since they weren’t moving laterally in front of us.

[I spent some time capturing some images from S&T's Jupiter moon simulator today, taking one hour apart snaps starting from 7:20pm PST 7/19/18.  In fact the inner pair is Callisto, moving out, and Io, moving toward Jupiter.  The outer pair is Europa, moving out, and Ganymede, moving inward.  But I definitely observed the line up and the movement in just those few minutes.]

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