Jimmy Westlake's Celestial News column appears monthly in the Steamboat Today.
Find more columns by Westlake here.
There’s a comet coming! Right now, Comet Hartley 2 is an unimpressive green blob in the constellation of Cassiopeia, but in the weeks ahead, it could blossom into the best little comet of 2010. It might reach fifth magnitude in mid- to late October, making it faintly visible to the unaided eye from dark sky locations. And, as a bonus, a NASA spacecraft will buzz only 600 miles from Comet Hartley 2 on Nov. 4, revealing small details on the heart of this icy interloper for the first time.
There are basically two kinds of comets, long-period ones that come around every million years or so, such as the famous Comet Hale-Bopp in 1997, and short-period comets that buzz past Earth every few years or decades. Halley’s Comet is probably the most famous of these. Comet Hartley 2 is of the short-period kind. Discovered in 1986 by Australian astronomer Malcolm Hartley, this little ice ball gets tangled up with Jupiter every so often, and Jupiter’s gravitational tug has shortened Comet Hartley 2’s orbital period around the sun to 6.47 years.
Comet Hartley 2 is small, even for a comet, and is not noted for putting on an impressive show, but this year’s pass is different, because it will skim only 11 million miles from Earth, its closest swing by Earth since its discovery. Its rapid motion across the sky will be evident from night to night, especially near the time of closest approach to Earth on Oct. 20, when the comet will be smack dab in the middle of the constellation Auriga. Unfortunately, the nearly full moon will overwhelm the faint comet around that time. You’ll do best to catch it the first two weeks of October and then again the first week or so of November, during the dark of the moon.
To spot the comet, go outside in the early evening around 8:30 p.m. and face the northeastern sky. There, you should see the familiar “W”-shaped pattern of Cassiopeia’s Chair, formed by five bright stars. Comet Hartley 2 is making its way below the “W” night by night during the first week of October. Although it might sprout a short tail as it gets closer to the sun and Earth, for now the comet looks like a faint, fuzzy, green cloud, somewhat like a dandelion head. On the evening of Oct. 7, the little comet will skim right past the famous “Double Cluster” of stars between the constellations of Cassiopeia and Perseus. Binoculars should show the beautiful star clusters and Comet Hartley 2 together in the same field of view. You can bet I’ll have my telescope out snapping pictures that night!
If standing out in the chilly night air with binoculars looking for green fuzz balls isn’t your idea of fun, you can sit back and relax until NASA’s Deep Impact spacecraft whizzes past Comet Hartley 2 on Nov. 4 and beams back amazing close-up photos of its icy surface. Only a few comets have been scrutinized at close range by spacecraft, so there still is much we can learn from this encounter.
For updates and current photos of Comet Hartley 2, keep an eye on the website www.spaceweather.com.
Professor Jimmy Westlake teaches astronomy and physics at Colorado Mountain College’s Alpine Campus. He is an avid astronomer whose photographs and articles have been published all across the world. His “Celestial News” column appears weekly in the Steamboat Today newspaper, and his “Cosmic Moment” radio spots can be heard on local radio station KFMU. Also, check out Jimmy’s astrophotography website at www.jwestlake.com.