Jupiter Shadow Transit Observing Report

I hope you  had an opportunity to observe the double shadow transit/occultation of Jupiter’s moons in the early hours of June 23rd. As I mentioned in the observer StarGuide this particular set of Jovian moon dances included transits and shadow transits of Galilean moons Europa and Ganymede plus an occultation egress of Io. I set up my 10” Dobsonian at about 0245 UT. The transit and shadow transit of Europa was more than 50% complete as Jupiter rose here in southern Indiana at approximately 0240 UT.

Unfortunately I set up the Dob on the wrong side of a tree and realized this at about 0255. While I was moving the Dob Io reappeared from it’s occultation behind Jupiter’s disc. By the time I had my gear moved it was about 0305 and when I got back to the eyepiece Io had emerged from it’s occultation. As Jupiter continued to rise out of the atmospheric murk I settled in to watch the transits and shadow transits of Europa and Ganymede. I live about two miles west of the Ohio river and the temperature inversions over the river keep the atmosphere low near the horizon very unsteady.

At 0305 Europa’s shadow transit had about 40 minutes remaining, Europa was transiting and Ganymede’s shadow was about 1/3 across Jupiter’s disc but I wouldn‘t see it until nearly 30 minutes later. Just a few minutes after Io’s reappearance it was easy to compare it’s size and Ganymede. At moments of good seeing the two moons seemed to take on a three-dimensional quality and I had the sense that Ganymede was closer than Io. I never caught a glimpse of Europa’s shadow. The atmosphere was too unsteady.

I tried various eyepiece and filter combinations and averted vision watching for Ganymede’s shadow. I began seeing hints of it around 0325-0330. As Jupiter climbed higher just before 0400 UT Ganymede’s shadow began popping clearly into view during moments of good seeing. I’d settled on a 15mm Plossl eyepiece with a 2x barlow and 82A soft blue filter. The next event was Ganymede’s ingress across Jupiter’s disc. I was able to discern Ganymede on Jupiter’s limb until 0415.

A few minutes later (0430) it was time for Europa to egress it’s transit of Jupiter’s disc. I watched as it appeared at Jupiter’s western limb at approximately 04:30:15. I continued to observe for a few minutes more. Ganymede’s shadow was very distinct during moments of good seeing. I stayed at the eyepiece until Europa cleared 4th contact with Jupiter’s disc.

In about 100 minutes at the eyepiece I watched Ganymede’s shadow transit, Ganymede’s transit ingress, Europa’s transit egress and Io’s reappearance from behind Jupiter. What an amazing show.

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All times are coordinated Universal Time.