Look for comet Lulin -- it won't be back for a million years
The pros are turning major amounts of telescope glass on comet Lulin; the rest of us can see it through binoculars
Throughout much of February, true early birds can catch a comet.Skip to next paragraph
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Comet Lulin -- formally C/2007 N3 (Lulin) -- is gracing the skies in the way-wee hours of the morning. It's still not clear if it will be visible to the naked eye later this month. But at the least, it should be a sweet binocular sight.
And catch it while you can. It won't be back for a million years. For a series of recent telescope-based images, you'll find a nice photo gallery here.
Its green hue comes from the gases it's giving off as it approaches the sun and its ices begin to sublimate -- change immediately from solid to gas. Two in particular -- cyanogen and bound pairs of carbon atoms known as diatomic carbon -- give the comet's fuzzy halo, or coma, and its tail the green cast.
Up in New England, for instance, look for Lulin about 3 a.m., clear skies willing. (For a rough cut at what your skies may be like, Canada's weather service has a nice "seeing forecast" site for North America here.)
The comet should sit about 20 degrees above the horizon in the constellation Libra. By Feb. 23, at the same time each morning, it appears in the southwestern sky about 40 degrees above the horizon near the planet Saturn. By then, according to the folks over at Sky and Telescope magazine, comet Lulin should be at its brightest.
For pros, this has been a tough comet to observe, said Lowell Observatory astronomer David Schleicher during a quick phone chat. It was first detected in July 2007 and through much of the second half of 2008 was too close to the sun -- or behind it -- to observe.
It popped back into view last month. But it did so when the moon was heading toward full, so the moon's glare made it tough to observe.
Still, he and other astronomers are giving Lulin a serious once-over now that it's getting brighter and the moon is on the wane.
Lulin turns out to be a very-long period comet, Dr. Schleicher explains; it orbits the sun roughly once every 1 million years. This puts it among the group of comets that originate in the Oort Cloud, a roughly spherical assembly of billions of icy objects that extends to about 18 trillion miles from the sun.
Schleicher and a colleague were able to grab photometry (light intensity) data last July as the comet was inbound and roughly 2.6 astronomical units -- 2.6 times the distance between the Earth and the sun -- away from the sun.
The ratio of dust to gas in the coma at the time indicated a "middle of the road" composition for the comet's surface. And it was unleashing water at a heavy rate, some 20 octillion molecules per second, he said. (Actually, he said 2 times 10 to the 28th molecules per second.)
Within the past couple of weeks, they've also been able to gather images that will help them study the shape of the nucleus and coma.
He notes that others have been using one of the Keck Observatory's 10-meter telescopes to study the comet at infrared wavelengths. So it shouldn't be long before researchers have a more-complete picture of this once-in-a-million-year visitor.