A Tall Tale Turns Out True!

My friend David Levine (shown here at left with wife Elinor at McDonald Observatory) was a buddy of mine from the local astronomy club, the Tucson Amateur Astronomy Association.  We shared similar interests, which included setting up for many public events, including the Grand Canyon Star Party, as well as more serious observing from TAAA dark-sky sites.  He had a way of telling a tale that was sometimes difficult to tell if it was true or not.  I could usually tell by the twinkle in his eye, but in the dark, it was harder to tell.  The Horsehead Nebula in your 8" telescope - Sure (wink-wink), I can believe that!  One of his stories involved observing a shadow transit on Jupiter, where the normally round shadow of the moon was crescent-shaped!  He was short on details, but indicated it was close to opposition when Jupiter was opposite the sun, rising at sunset, and the moon itself was blocking part of it's shadow.  Well, I had never heard of such a thing, and I've been around the block a few times, but he swore it was true!

Well Dave died a few years back but that tale has always stuck with me, and it just so happened that early yesterday Jupiter was at opposition.  Looking at a Javascript for the moon positions, it happened that Europa had a shadow transit about 6 or 7 hours past opposition - time for an adventure!  Since I work at Kitt Peak part time at their Nightly Observing Program, I was able to reserve the telescope for after the program.  There was a bright moon, so little demand for a late-night program.  Unfortunately, the shadow transit didn't start till after 2am local time - hard for a school night, but hey - these myths need to be dispelled!  I packed my webcam and laptop and headed to the Observatory after my wife left for her NICU shift.

It was a great, clear night and better-than-average seeing given the blustery breeze that was blowing.  I spent a couple hours trying some wide-field images in the moonlight, waiting for Europa to move into position.  Finally it was time to get set up - I've got little experience with the Imaging Source camera I got about a year ago, so it was a great night for some practice on the 20" scope.  The state-of-the-art of planetary imaging these days involves taking video sequences and taking the best images to stack into some truly amazing photos, and the camera/telescope combo worked well.  I took 2 minute sequences every 10 minutes or so and 3 of them are shown here.  At left Europa is shown approaching from the east and at right it is shown 20 minutes later as it casts it's shadow on the disk.

 

And some 70 minutes later, about the time I stopped with some thin cirrus moving in, the moon and shadow had crossed over halfway across Jupiter's disk.  The Great Red Spot had also rotated into view, and you can see a smaller red spot near the moon/shadow image.  Given the quality of the night, and that the seeing had deteriorated to about average, I'm amazed at how well these images came out.  And also, you can see that the disk of Europa indeed does occlude part of the black round shadow, a crescent shadow being the result - Dave was telling the truth!  A new observation for me, but I'm thinking that it has to be done within a few hours of opposition, and also, it will most likely occur for the inner moons Io and Europa.  I'm thinking the longer projection distance of the outer moons would make it more difficult to observe.  And yes, after disconnecting the camera and putting it away, I looked for seeing the partial shadow visually.  When waiting for moments of good seeing, yes, the crescent shadow could be seen, so it is possible to see with your own eyes.

 

Well, it was  long day at work after almost 3 hours of sleep, but it was a great adventure, and I'm glad to harken back to the old days sitting and talking astronomy with a dear departed friend.  The use of the 20" RCOS telescope is courtesy NOAO/AURA/NSF.