Post by Paulie pchris00 on Aug 25, 2012 10:28:08 GMT -6
I didn’t work last Tuesday, specifically so I could attend the CA/CPD star party on Northerly Island. But I was feeling rather lethargic, and some lingering issues with my car caused me to stay home instead. I slept for awhile, then got up around 4 AM to get a look at the Jovian system. I wasn’t disappointed.
When I first observed Jupiter, I only noticed three of the Galilean Moons. I looked around for a dark spot on the Jovian cloud tops, indicating a shadow transit of the missing moon, but didn’t notice one. Now, I’ve seen the Jovian system more than most this summer, but I haven’t been getting more than an hour or two a week since late June. When I’m spending a lot of time observing the Jovian system, I don’t need any charts or tables to tell the Galilean Moons apart, or when they might transit (within a day or so). My Jovian observing skills were obviously rusty, and being limited to 6” aperture didn’t help either. According to Sky & Telescope’s tool for locating the Galilean Moons, there was indeed a shadow upon Jupiter when I first observed, though it wasn’t the missing moon. But I didn’t know any of that at the time, and trusted my skill more than I should have.
Europa, which appeared close to Jupiter when I started the session, and seemed to be moving towards the planet, also had its shadow near the opposite limb. Somehow I missed seeing it, and my camera wasn’t capable of picking up that detail. The morning air was cold and damp, and made my bad knees ache something awful. I took a short break before going back to time when Europa disappeared, still not sure it if was going to transit in front of Jupiter, or be eclipsed behind it.
Overexposed to emphasize Europa.
When I came back to the eyepiece about 4:55 AM CDST I found a surprise: Io had emerged from the opposite limb that Europa was approaching. All four moons were visible, but not for long. I marked first contact for Europa at 5:00 AM CDST. I could still see Europa as it crossed in front of Jupiter. Timing second contact of a Galilean Moon transit proves even harder than second contact on a Venus transit. Instead of a big, dark target on a big, bright background, a Galilean Moon transit is a not so bright, tiny disk transiting onto a somewhat brighter background. I found it very hard to time. I could see Europa for several minutes in front of Jupiter, but couldn’t discern when the moon was fully upon the Jovian disk. All I can say is that is was sometime between 5:05 and 5:10 AM CDST. Yeah, it was much harder than finding Venus’s second contact time. Sky & Telescope gave a first contact time of 10:00 UT- or 5:00 AM CDST. That matches my observation. S&T doesn’t give internal contact times, so I have no idea what time Europa was fully transiting Jupiter. At 5:10, I could no longer see Europa; it blended into the Jovian disk.
Io, after transit egress.
I watched for 24 more minutes as Io continued to distance itself from Jupiter. Morning twilight was quickly brightening the sky. There was nothing more I could expect to observe, so I turned my attention to the trio of morning planets spaced out along the ecliptic. It was time to call the session. It was the first time in a long time that I’ve observed the ingress of a Galilean transit. I hope to catch quite a few more as the Jovian system approaches opposition.
When I first observed Jupiter, I only noticed three of the Galilean Moons. I looked around for a dark spot on the Jovian cloud tops, indicating a shadow transit of the missing moon, but didn’t notice one. Now, I’ve seen the Jovian system more than most this summer, but I haven’t been getting more than an hour or two a week since late June. When I’m spending a lot of time observing the Jovian system, I don’t need any charts or tables to tell the Galilean Moons apart, or when they might transit (within a day or so). My Jovian observing skills were obviously rusty, and being limited to 6” aperture didn’t help either. According to Sky & Telescope’s tool for locating the Galilean Moons, there was indeed a shadow upon Jupiter when I first observed, though it wasn’t the missing moon. But I didn’t know any of that at the time, and trusted my skill more than I should have.
Europa, which appeared close to Jupiter when I started the session, and seemed to be moving towards the planet, also had its shadow near the opposite limb. Somehow I missed seeing it, and my camera wasn’t capable of picking up that detail. The morning air was cold and damp, and made my bad knees ache something awful. I took a short break before going back to time when Europa disappeared, still not sure it if was going to transit in front of Jupiter, or be eclipsed behind it.
Overexposed to emphasize Europa.
When I came back to the eyepiece about 4:55 AM CDST I found a surprise: Io had emerged from the opposite limb that Europa was approaching. All four moons were visible, but not for long. I marked first contact for Europa at 5:00 AM CDST. I could still see Europa as it crossed in front of Jupiter. Timing second contact of a Galilean Moon transit proves even harder than second contact on a Venus transit. Instead of a big, dark target on a big, bright background, a Galilean Moon transit is a not so bright, tiny disk transiting onto a somewhat brighter background. I found it very hard to time. I could see Europa for several minutes in front of Jupiter, but couldn’t discern when the moon was fully upon the Jovian disk. All I can say is that is was sometime between 5:05 and 5:10 AM CDST. Yeah, it was much harder than finding Venus’s second contact time. Sky & Telescope gave a first contact time of 10:00 UT- or 5:00 AM CDST. That matches my observation. S&T doesn’t give internal contact times, so I have no idea what time Europa was fully transiting Jupiter. At 5:10, I could no longer see Europa; it blended into the Jovian disk.
Io, after transit egress.
I watched for 24 more minutes as Io continued to distance itself from Jupiter. Morning twilight was quickly brightening the sky. There was nothing more I could expect to observe, so I turned my attention to the trio of morning planets spaced out along the ecliptic. It was time to call the session. It was the first time in a long time that I’ve observed the ingress of a Galilean transit. I hope to catch quite a few more as the Jovian system approaches opposition.