Jimmy Westlake's Celestial News column appears monthly in the Steamboat Today.
Find more columns by Westlake here.
Comet C/2007 N3, better known as Comet Lulin, is zooming past the Earth this week on its whirlwind tour of the inner solar system. Some comets are in orbits that periodically bring them back to the inner solar system, but if astronomers are correct, Comet Lulin has never been here before and will never be back again. Better enjoy it while it's here.
What are comets? Astronomers think of them as the frozen leftovers from the formation of our solar system nearly five billion years ago. A typical comet is about 10 miles across and made primarily of frozen water and other exotic ices. Unlike the planets, whose orbits are nearly circular, comets are in highly elongated orbits that carry them from the cold recesses of the outer solar system into the hot inner solar system during a period of hundreds, thousands or even millions of years. It is only when a comet enters the inner solar system that it swells and grows its characteristically beautiful tail. The pressure of sunlight and the solar wind blows the comet's vapors and dust away from the sun and out of the solar system.
Everything about Comet Lulin seems backwards. It orbits in the same plane as the major planets, but in the opposite direction. And rather than pointing away from the sun, its dust tail seems to point toward the sun. Comets orbiting the sun backwards are not all that unusual. In fact, the most famous of all comets, Halley's Comet, orbits backwards. What is unusual about Comet Lulin is that it does so in the same plane as the planets, like a fish swimming upstream. Consequently, when it passes only 38 million miles from Earth this morning, Earth and comet will pass each other at the dizzying speed of 140,000 mph. After that, Comet Lulin will quickly fade into the distance. Its quirky anti-tail that points toward the sun is really an optical illusion caused by our line-of-sight view straight down the tail. Lulin's sunward-pointing anti-tail is, in reality, curving off behind the comet, but it appears to project itself out in front. In 1957, Comet Arend-Roland also displayed an unusual anti-tail toward the sun.
I love comet-watching for two reasons. First, comets bring excitement to a sky in which not much changes except during centuries or millennia. Second, every comet is different and has its own unique personality. One never quite knows what to expect when a new comet is discovered.
Such was the case when astronomers at China's Lulin Observatory discovered this most recent comet in 2007 while still far from the sun. After a year and a half of waiting, Comet Lulin now is bright enough to be spotted with the unaided eye from dark sky locations. It sailed past the bright planet Saturn earlier this week, and now Comet Lulin will be cruising through the stars of Leo the Lion, including a close pass by Leo's brightest star Regulus on the night of Feb. 27. This comet is no Hale-Bopp, however, so use binoculars to help you spot the green fuzzball and its short, spiky tail. For finder charts, updates and a Comet Lulin image gallery, check out the NASA-sponsored Web site Space Weather. You might even spot some of my comet images there. Happy comet-watching.
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 around the world. Find his Web site at www.jwestlake.com.