Tuesday, November 2, 2010

Dual Transits of Ganymede & Europa, Oct. 30-31

Last Saturday night I was looking forward to observing the many events involving the Galilean Moons, but I was also committed to doing something Halloweeny with Hillary. We even had a public argument on Facebook about what to do that night. Enter Chicago Astronomer Patrick to save the night for us, and mix astronomical observing with a Halloween themed Séance party at his Saki record store in Chicago. This was something for both of us to enjoy.



The night’s events, Galilean and otherwise, were to start around 7 PM, and we arrived right on time. Patrick saw us walking up to the store and came out to greet us. I was tempted to grab my Dob for a quick look-see at the Jovian system, but thought better of it. In hind sight, I should have, since Ganymede was due to start it’s transit at 7:15. We had no observation of Ganymede before it disappeared in front of Jupiter’s disk.

Observations were made in front of the store between 7:40 and 7:45, with lonely Callisto far off to the right (inverted image), Europa nearing Jupiter from the right, and Io off to the left. More observations were made between 8:30 and 8:46, to confirm trend of motion. We had something of an audience both times, mostly curious party-goers out for a smoke break. We shared the Jovian system with pleasure, explaining how each of the inner three Moons would be interacting with the planet that night.



Hillary in front of the store. It was a fun spot to observe, with costumed people coming by to have a look at Jupiter & Moons.

Although the forecasts were favorable for a clear night of observing, during the second round of viewing clouds were starting to move in from the Lake. Not cool, but they were scattered, and could be dealt with.

Since we had missed Ganymede’s point of contact to start it’s transit, our first observed event was the start of Europa’s transit, scheduled to occur at 9:22. Clouds were increasing, and seeing conditions had deteriorated, and I thought I observed first contact at 9:17. The total transit was to begin at 9:26, and this fits with what was observed, although between clouds, Europa could still be discerned near the limb until at least 9:33. The show had already ended, and Patrick had left to go home and feed his pets a few minutes before. When the clouds became impenetrable, I concluded observations in front of the store, and Hillary and I met Patrick at his house.

When we arrived, we had a few minutes to kill before the next event, Ganymede reappearing on the left limb (again, all of these descriptions are based on an inverted view). Patrick treated us to green tea before heading down the street to Sunken Gardens Park, my Dobsonian in tow. Ganymede was set to emerge at 10:15, with last point of contact at 10:25. Seeing conditions were still bad, but the clouds were not as bad as when we left the store. Therefore, Ganymede was not seen emerging from the limb until 10:21. Once we had all seen Ganymede slipping away from it’s master, it was already time to get ready for the next event, Io disappearing behind Jupiter. For a few minutes, though, we had the two moons together, just to the left of Jupiter.

The partial occultation of Io, starting at 10:33, was observed as best as could be done. At 10:36, Io was still partially visible, and should have been for at least another minute, but a cloud moved in and stole the moment of total occultation. With half an hour before the next event, we bounced around the sky. Orion was showing above the trees, and the Great Nebula was observed and discussed, particularly the 3D depiction of it in the Hubble IMAX film.

By 11:00, it was time to turn attention back to the Jovian system. Ganymede and Europa’s shadows were to fall upon the great disk in short succession, Ganymede starting at 11:04, and Europa at 11:14. Due to foreshortening on the limb and poor condition (saying nothing of my scope’s imperfect collimation), Ganymede’s shadow was not observed until 11:18, with separation from the limb noticed at 11:21. Europa’s shadow was more subtle, and I do not have it noted when it was first observed. Cloud cover thickened at 11:26, so we returned to Patrick’s house to warm up and refill mugs of tea. Although we returned for one last round at midnight for Europa’s emersion from the Jovian disk at 12:06, I do not have Europa noted as visible until 12:11, just as it’s partial transit was ending. The late night chill and worsening clouds cut our session short after that.

Hillary and I hung out for a little while before calling it a night, and heading back to Indiana. As Patrick’s Moon images above show, conditions did improve after we left, but I think we made the right call. We had seen a number of Galilean events already, more than I normally see in a good week. Patrick and Hillary are free to comment, but I will readily admit that after the first observation in front of the store, I was very focused and determined to stay on schedule, and observe every subsequent event after that. It was one of my most disciplined observation sessions ever, despite setting up and breaking down (Patrick is maybe slightly jealous of this capability) five times during the course of the night, at two locations. I like my leisurely tours of the sky when I’m alone, but this was an action packed night out in the Jovian system, and I wanted to document it as best possible. Unfortunately, my images are not worthy of posting, and don’t prove much of anything, except that I have a lot of ground to make up in the realm of astrophotography. Thank you to Patrick for hosting Hillary and me. I had a fun time, both at the Saki Séance party, and the observing during and after. And thanks to both of you for putting up with my single-mindedness of what’s next, what’s next, what’s next???


  1. Good posting Paulie and I am glad you are able to set up and take down so quickly and easily. What were some of the reactions from the folks who saw the events at the store? I missed it here due to weather :( Nothing like watching the parading moons of Jupiter.

    Grab and go astronomy !!!!!!

  2. I wasn't really sharing any events in front of the store. I don't think anybody was even out for Europa's first transit contacts, which was the only event while we were there. I don't think I would have shared it anyway. I was trying to gather data (not exactly precise, but close enough for my purposes). When those moments catch me off guard, I'm okay with sharing them, but this was something I had specifically requested off work to witness, and witness it I would. Non-astronomers be damned. Hillary and Patrick were free to view but this was for the hard core geeks.