jupiter, moon, repeat

The last few nights have been relatively cloudless and with pretty good seeing. But, there was always moisture blowing in from the ocean: a kind of grainy dust which you could actually see blowing past the moon. It caused the moon to have a large halo, and scattered enough light through the sky that I didn’t bother trying for doubles, since many on my list were faint pairings and I didn’t have the right conditions for those. As a result I stuck to the bright objects, Jupiter and the moon.

Jupiter always showed a great amount of detail, especially dark breaking-wave shaped festoons arcing from the NEB into the center band. On the night of 3 July it appeared the festoon was moving very rapidly across the face. This night was special too because there was a Galilean moon transit (Io), where the shadow seemed to precede the moon before it transited. In fact, the shadow near the eastern limb was from a moon which was already far progressed through its transit and was close to the western limb – but not visible. It was a very steep sunlight angle which caused the shadow to lag so far behind. Europa was approaching the limb and was not casting its shadow on it yet. The sequence was:

3:03 I Tr I
4:18 I Sh I
4:42 II Tr I
5:14 I Tr E
6:27 I Sh E
7:12 II Tr E
7:20 II Sh I
9:42 II Sh E

I saw I Sh I, II Tr I, and I Tr E. What’s interesting is Io had a very fast shadow transit, but its egress happened while the shadow was still on the planet. Europa, on the other hand, started and finished its transit before its shadow was even cast on the planet – showing just how steep the sunlight angle was and also that it is farther away from Jupiter than Io.

3 July I also happened to catch a meteor, of all things, shooting between Arcturus and CVn. It was quite a surprise given the moon haze and light scatter.

5 July was the best seeing, with a lot of turbulence all over the planet, including a festoon which forked in two.

For the moon I generally followed the terminator and looked at mountains on the limb. I used the Tele Vue Planetary filter and find while its much brighter than the moon filter (my eye is burned with an afterimage) I feel I see more detail and have better contrast. It struck me that the shadows on the moon are far blacker than what you might find on earth’s terminator – the shadow lines are sharp and there is little or no grayscale change. I assume this is because of a lack of atmosphere which might otherwise scatter light into the shadows and make them appear brighter. The night of the 5th I used 553x and saw a lot of jagged edges, floating mountains, and weird peninsulas along the terminator. Quite remarkable.