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Health, Science, Environment

Comet Lulin makes a unique appearance

This article first appeared in the St. Louis Beacon, Feb. 20, 2009 - Stargazers willing to brave the cold and stay up until midnight or later will observe a once-in-earth's-lifetime event this month. Possibly with the naked eye, and certainly with binoculars, they will be able to observe the newly discovered Comet Lulin on its trip through the inner solar system.

Lulin is named for the Taiwanese observatory where it was first seen in July 2007.

Comet Lulin will look like a greenish fuzzy blob, with a very bright center and probably a tail. It will appear much bigger than a star.

It should be brightest on Tuesday, Feb. 24, its closest approach to the Earth. At that time it will be half the distance between the Earth and the sun -- about 38 million miles away and traveling at 31 miles per second toward the outer part of the solar system.

Under good conditions the comet is visible now.

"Comet Lulin is currently in the constellation Virgo, heading very quickly toward the constellation Leo," said UMSL astronomer Erika Gibb.

"Virgo rises in the Southeast around midnight. On Feb 16, it is very near the bright star Spica in Virgo. On Feb. 24, when Lulin is closest to Earth and should be brightest, it will be pretty close to Saturn, which is currently near the back foot of Leo. On Feb. 28, Lulin will pass very close to Regulus, the bright star at the bottom of the backward question mark pattern of stars that make up Leo's head (Leo is the lion)."

What are comets, and why are they so exciting?

Obviously, comets are exciting to lay observers because they look so cool.

Basically, the comet will rise in the east and move up in the night sky until it is overhead. On Monday, Feb. 23, it will be just east of Saturn, which appears as a very bright star. On Tuesday, Feb. 24, when it should be brightest, Comet Lulin will rise at about 10 p.m., and be straight overhead at 1 p.m. On Feb. 28, it will be straight overhead by midnight.

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They are small objects, less than 100 kilometers in diameter, about half ice and half dust. They are too small to detect until they get into the inner solar system, where the sun warms them, vaporizing part of the water vapor and releasing dust. 

The dust and gas form the comet's "coma" that makes it appear fuzzy. Some of the dust also forms a visible tail that can extend several million kilometers, always pointing away from the sun. A comet can also have an "ion tail" of charged particles created by solar energy.

To astronomers like Gibb, comets are exciting because they were created at the same time as the solar system, about 4.5 billion years ago. She will be able to collect data on organic matter from these vaporizing pieces of primordial matter. To do this, Gibb will be analyzing the spectra of light wavelengths emitted by the comet using special telescopes. The spectra will tell her what elements are present in this very hot dust. Each element when heated gives off light that can be separated into a characteristic pattern of wavelengths called spectra.

Why is Comet Lulin a once-in-Earth's-lifetime event?

This comet is thought to come from the Oort cloud, a spherical shell of comets surrounding the solar system. At the beginning of the solar system, the gravity of the giant planets -- Jupiter, Saturn, Uranus and Neptune -- flung these little fragments away to form the Oort cloud.

Comet fragments normally stay in the Oort cloud. But sometimes a passing star will give one a little tug and send it either into space or into the inner solar system where Earth resides. Comet Lulin is following a hyperbolic orbit. Therefore, after it circles the sun, it will go back to outer space, either to the Oort cloud or beyond. (Comets are too small for observers to continue following their paths into outer space.)

It will not come back.

For photos of Comet Lulin taken in St. Louis by Greg Ruppel, click here .

Jo Seltzer is a freelance writer with more than 30 years on the research faculty at the Washington University School of Medicine and seven years teaching tech writing at WU's engineering school.

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