Churning Whitecaps

Last month I offered an introduction to Jupiter observing. I hope by now you've had a chance to see the major bands, the satellites and their shadows, and maybe the GSfkaR (the Great Spot Formerly Known as Red). But what more can you see there?

Wait for a night of steady seeing, and crank up the magnification (over 200x, or higher if you can), pull up a chair so you're comfortable at the eyepiece, and you'll see a great deal more! Let's start with that red spot, the GRS. Dangit, it's not red, right? But don't be disappointed by the color; instead, take a close look at the area where the SEB (that's the southern equatorial band, if you missed last month's column) rejoins after splitting around the spot. The spot itself is a swirling maelstrom of a cyclone, and it stirs up the atmosphere around it and causes a huge zone of turbulence in its wake. Think of the churned-up whitecaps swirling around behind the propeller of a speedboat - only what's being churned are the red and white bands of Jupiter's atmosphere, and that means you can see the churning with a telescope. For a sample of what it looks like, look at the June 1999 Hubble image.

See all the red and white swirls behind the GRS? You can actually see those in your telescope, on a night when the atmosphere is steady. Try sketching what you see - don't worry whether it has artistic merit, because the point is to focus your attention on the details you're seeing, which in turn will help your mind train your eye to see more detail.

Want some other challenging Jovian targets? Look for festoons - long dark streamers (some people see them as blue) sweeping from the north or south equatorial bands into the pale equatorial zone. You can see some excellent examples of festoons in that Hubble image, coming off the NEB just above the GRS (remember, the spot is in the south, so the NEB is the band that doesn't have the spot in it). Festoons change over a period of a few weeks, so you can watch them appear, disappear, or lengthen if you watch Jupiter regularly. While you're looking at the light equatorial zone, look for the thin, dark equatorial band (EB). It's much subtler and harder to see than the NEB and SEB, and it's a good target as you learn to look for subtle detail on Jupiter. You may also see smaller features in the NEB and SEB, such as the small dark spots, probably cooler areas of cloud, called "barges", and the white ovals which appear, migrate, and merge.

Uranus, Neptune, and Pluto are in the morning sky - visible to the late-night owl or the early riser. Saturn and Mars hang low in the west in early evening. They're still visible throughout the month, but look now - they'll be harder to see next month. On the 24th, Saturn and Mars pass within a couple of degrees of each other.

Venus is even lower, a change after its high pass over the past month - but now is actually an excellent time to catch Venus because throughout the month it will shrink to a thin crescent and meanwhile it will grow in size as it draws closer to us. Take a look every few days, and you'll see its size and phase change, even in the smallest telescope.

Finally, although the event won't happen until June 8, it's worth mentioning Venus' upcoming transit of the sun. Why? Because it won't be visible here - but a Venus transit is an exceedingly rare event, and some dedicated planet-watchers may want to schedule a vacation during this time. (How rare? The last Venus transit took place in 1882; the next one will happen in 2012, and after that there won't be another one until 2117.) If you do travel for it, don't forget that you'll need a solar filter, if you don't already have one.

The transit happens at 2 am our time, which is why we won't see it - the sun won't be up. The path of visibility includes the eastern half of the US, where it will be already in progress at sunrise: the farther east you go, the longer you'll have between sunrise and when Venus' shadow exits the sun's disk. Going farther north helps, primarily because the length of the day increases (go above the arctic circle, and you get to see the whole thing!) and if you were contemplating a trip to Europe, Africa, Brazil, or Asia, those places all get excellent views (weather permitting, of course). For details, check out the map at http://sunearth.gsfc.nasa.gov/eclipse/transit/venus/ - there's lots of other useful information about transits on that site as well.

Stay tuned next month, for more tips on transit viewing. And until then, there's plenty to keep you busy on Jupiter!