A huge storm which has been raging as long as humans have had telescopes ...
Jupiter is at opposition this month!
This means that it's your best chance (until next year) to observe all the fascinating detail of Jupiter's turbulent atmosphere. This year it's been phenomenally active, much more so than most years. The ALPO Jupiter mailing list (http://groups.yahoo.com/group/ALPO_Jupiter/) has been buzzing with discussions of the many new storms which have appeared on Jupiter this year.
Even better, it looks like we're having better seeing here this winter (at least when it's not cloudy or raining!) than we've had for several years. And Jupiter is big enough that you can see lots of detail in just about any telescope - I've done plenty of observing and sketching the giant planet through my 80mm f/7 refractor.
To follow discussions like that, or to track your own observations from night to night, you need to know a little about the terminology of Jupiter's atmospheric features. I've added labels to this sketch made at Fremont Peak a few years ago by member Jane Houston Jones, using a 7" refractor. South is up in the sketch.
The dark and light bands are formed by clouds of different temperatures, heights, and compositions within Jupiter's atmosphere. The dark bands are called "belts," or, sometimes, "bands," in contrast with the off-white "zones" between them. They appear brownish or reddish to most observers. Belts are named and abbreviated according to position on Jupiter: Equatorial Belt, South Temperate Band, and so on. The NEB, SEB, and the two Polar Regions are easy targets and should show up in any telescope, perhaps even high-powered binoculars if mounted on a tripod. Most of the other belts are more difficult to see, and require steady seeing and good optics. Note that even with the excellent seeing and excellent optics when this sketch was made, the EB was not visible. This is fairly typical - it's one of Jupiter's more elusive features. The highly detailed banding in the north polar region (e.g. separating the NNTB from the N3TB from the polar region) is also difficult and takes very steady skies.
The Great Red Spot (GRS) is Jupiter's most famous feature. A huge storm which has been raging as long as humans have had telescopes to look at Jupiter, it changes color and location over the years. It is fairly pale now, as the sketch shows (though it may be a little darker this year than last year, when the sketch was made). It sits within a hollow in the STB, called the "Great Red Spot Hollow", and often the hollow, where the dark band separates to make room for the GRS, is more obvious than the spot itself.
Festoons are another commonly observed feature. Blueish, in contrast with the reddish belts, they usually sweep out of the temperate bands (especially the NTP) into the EZ.
"Barges" are dark spots that migrate within a band. They aren't well understood; they may be areas of cooler cloud. This year Jupiter is also showing some noticeable dark stripes, particularly in the NEB.
A treat in the past few years has been the collection of white ovals, especially leading and following the GRS in the STB. White ovals can be either cyclonic or anticyclonic storms. On a night of steady seeing, an amazing amount of detail can be seen, and what initially appears to be a split in a band can turn out to be a complex of white spots of all sizes. ALPO and other observing groups track these white ovals, and issue alerts as they appear, disappear and merge, and have reported an unusual amount of activity in the last few years.
Are there other planets to look at? Sure!
Saturn is running a couple of hours ahead of Jupiter. Look for the bright object sharing the head of Taurus with Aldebaran, then point your telescope and enjoy the lovely view of the wide-open rings (tilted about 25 degrees from horizontal, still enough to follow the outer ring all the way around the far side of the planet). With the rings that open, it's also easier than usual to see the thin gap in the outer ring, and ambitious observers can look for the radial "spokes" in the B ring which show up in Voyager and other spacecraft photos. We unfortunately just miss the daytime occultation of Saturn on the 20th (hop in the car and drive south to northern LA county if you don't want to miss it), but Saturn will make a close approach around 3-4pm on that day, and should be a nice sight in a low-power telescope or binoculars.
Mars is still visible in the early evening sky, getting lower as the month progresses. It's too far away to show much detail through a small earthbound telescope, though. Later in the month, Venus returns to evening skies, showing a nearly full phase. Mercury moves into the morning sky, but stays low and close to the sun. The outer three planets - Uranus, Neptune, and Pluto - are all too close to the sun to be easily observable this month.
Palm pilot users: I wrote a couple of new Palm programs to show the moons of Jupiter and Saturn (and the GRS and shadow transits on Jupiter). They're free (and open source) for anyone who can use them. Go to http://www.shallowsky.com/software/ for more details.
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