Don’t Miss What’s Right Over Your Head

Hiding over your head the next couple weeks is December's version of Cassiopeia - an M instead of a W. Created with Stellarium

I bet you haven’t looked up lately. Way up. I know I didn’t until last night and there I saw it, literally hiding in plain sight, the constellation Cassiopeia the Queen. When it ascends the northeastern sky in early fall, you can’t miss the group’s striking W or zigzag shape. By the time December rolls around, Cassiopeia’s still there, but it’s too high up to get noticed by many of us. Here in Duluth, between 8 and 9 o’clock in the evening, the W, now transformed into the letter M, is pitched in the northern sky a little more than an outstretched fist from the sky’s overhead point or zenith.

I suppose the best way to enjoy a view of the Queen is simply to lie down on your back and look up. No neck strain necessary. And take your binoculars with you. The Milky Way flows right through the constellation. Sweeping across the M will reveal hundreds more stars than you can see with you naked eye and at least a handful of fuzzy spots, where stars are gathered into star clusters.

Jets of water ice spray blast from from the south polar region of Saturn's moon Enceladus at approximately 670 mph. This raw, unprocessed image of Enceladus was taken on November 30, 2010 and received on Earth December 1, 2010.

The Cassini probe at Saturn dipped to within 30 miles of Saturn’s icy moon Enceladus (en-SELL-ah-dus) last Tuesday and sent back the first photos the following day. The raw image above shows the moon just as the spacecraft did. The sun was hidden by the moon, providing the perfect backlight to highlight the moon’s misty fountains of fine ice particles. They remind me of the plumes blasting from the snow machines on our local ski hill, Spirit Mountain. Scientists believe the plumes originate from reservoirs of underground water.

Artist's view of water vapor plumes escaping from fault lines in Enceladus' surface. Credit: NASA/JPL

Enceladus has a very stretched out (eccentric) orbit causing its distance from Saturn to vary during the 1.4 days it takes to circle around the planet. The difference in the force of gravity between close and far stretches and squeezes the little moon. Rub your hands together and you’ll feel the heat of friction. The change in gravitational force – called tidal forces – cause the fault lines in Enceladus’ southern hemisphere to rub back and forth against each other, producing the heat that melts the water and powers the geysers.

The photo also has other interesting details. For one, the moon is lit not by the sun, but by sunlight reflected by the planet Saturn, which is out of the frame. Then there’s that strange shadow extending up over the plumes on the left. I agree with Phil Plait, who writes the Bad Astronomy blog, that we’re probably seeing the shadow cast by Enceladus itself cutting off some of the sunlight that would otherwise light those plumes as brightly as the others. Any way you look at it, the view is spectacular!

The newly emerging SEB (the dark, loopy strand just below middle in the left image) is in good view tonight. All is still quiet in Jupiter's opposite hemisphere, which features the famous Great Red Spot. North is at top in the pictures. Images credit and copyright: Christopher Go

For Jupiter watchers, tonight’s a good night to watch for the return of the planet’s South Equatorial Belt (SEB). The hemisphere that shows the darkening of the belt is favorably placed for observers in the U.S, Canada and South America. The best time for viewing is around 7:30-8:30 p.m. CST. Chris Go’s photos show well how far along the change has come since the beginning of the revival in October. To see it best, you’ll need at least a 6-inch telescope, medium to high magnification and steady (unturbulent) air.