Another Jovian transit

Started by darrencrooks, 04/11/2003 05:06AM
Posted 04/11/2003 05:06AM Opening Post
Finally a clear night after a week of snow, freezing rain, and ice pellets. Got out to a friend's back yard last night, where seeing is much better than my light-strewn driveway, and passed a pleasant evening of viewing.

I found tube currents to be a bit of a distraction when viewing Jupiter,even after letting my humble 4.5" DS reflector cool for an hour (saw the GRS coming into view around the western limb about 0330 UT -- nice!), but the view of Saturn was quite sharp and steady. The Cassini division was easy at 135X (6.7mm Meade Series 3000 plossl), and I could make out surface detail as well ... a tannish band near the equator, and a brownish dot at the north pole). The moon was spectacular. Mountain ranges, valleys, rilles, craters ... they just sprang up in sharp relief.

A real treat was seeing both M44 and Jupiter in my buddy's 8" Meade SCT using a wide-field eyepeice ... beautiful. So was M42, which showed some gorgeous detail even when near the horizon, under a quarter moon.

And a bonus! Got Mercury just before it disappeared behind the trees. First time!

Tonight I was out again with my 4.5" reflector (which I have decided to christen Heep, by virtue of its being so 'umble) and again got some excellent views of both Jupiter and Saturn. I find Saturn to be less of a challenge than Jupiter. The Cassini division was again very sharp, this time at 90X with a 10mm Silvertop plossl. I could even see faint surface banding with the same eyepeice. Once the scope cools down enough, Saturn shows a rock-steady image that rarely changes ... but Jupiter! That's another story. So many features seem to appear out of nowhere only to be lost again just as quickly. But this night I sat patiently for about 2 hours, watching Jupiter, starting around 0300 UT.

I was watching what I thought was a shadow transit of Io. But at about 0400, I saw another black dot appear on the following limb ... and realized that the first tiny speck I saw was not the shadow of Io, but the moon itself. Another first. The Jovian disk was clear and sharp this night, and although the polar regions were not ask well defined as I had seen them before, I did notice a thin, sharp line running between the equatorial belts, neatly bissecting the planet. This feature was discernable only with difficulty, and disappeared from time to time. Another feature I hadn't seen before was a division in the SEB itself. At times it appeared as though the SEB were split in two. This was using my 6.7mm plossl.

All in all, an exceptional couple of sessions for planetary observing. Heep and I can hardly wait for Mars!

Sharp, steady seeing,
Darren
Posted 04/11/2003 01:38PM #1
Thanks, Ed. I couldn't see the other moon (Io). Not dark enough, I suppose? It really did look like two shadows. So I figured the first one must have been Io, because the shadow was so close to it.

Interesting confluence of events. I bet it's not often that two moons are passing across the face of Jupiter at the same time!

So when one of the outer moons transits Jupiter, I'm assuming that the shadow does not become visible for some time thereafter, because I never saw Callisto's shadow, just Io's.

Do you have a URL for Java Jupiter?

Thanks and clear skies,
Darren
Posted 04/11/2003 03:07PM #2
I had the same experience - I hadn't seen Callisto transit before; you couldn't have convinced me at the eyepiece that I wasn't seeing a shadow! I only confirmed this later. By the time I left the eyepiece Callisto and Io's shadow looked like two beady eyes peeking out between the equatorial belts.

I was able to see Io during (very) occasional moments of very good seeing (although I only got what I was seeing sorted out later). Busy night on Jupiter.