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Sun-watching satellite spots 500th comet

The sun is to the lower left in this SOHO image of C/2002.
The sun is to the lower left in this SOHO image of C/2002.  

By Richard Stenger

(CNN) -- A spacecraft in orbit 1 million miles from Earth has detected its 500th comet, making it by far the most prolific comet hunter ever, according to solar scientists.

The satellite, known as the Solar and Heliospheric Observatory, or SOHO, needed less than six years to discover the milestone comet.

The $1 billion orbiter, a joint operation of NASA and the European Space Agency, trains an array of instruments on the sun, giving it ample opportunity to spy the primordial ice boulders as they fly near or right into our parent star.

"SOHO-500 was very faint compared to many other more spectacular sun grazing comets," SOHO scientist Paal Brekke of NASA's Goddard Space Flight Center in Greenbelt, Maryland, said this week.

Dreaming of discovery

Comet Ride
Interactive comet tour 
Iceball Gallery
Pictures of cool SOHO comets  through the years

Amateurs identified most of the comets, spotting them while perusing raw sun images and movies on the SOHO Web site.

No. 500, officially known as C/2002 P3, was reported by Rainer Kracht of Germany on August 12.

"Analyzing SOHO data is a great challenge and you have to combine many skills," Kracht said. "But every amateur astronomer dreams of finding a comet."

Most SOHO comets were found in pictures from an instrument called the Large Angle and Spectrometric Coronagraph, or LASCO.

"Though LASCO was not originally built for this purpose, no other instrument has discovered more of these comets," said Bernhard Fleck, a SOHO researcher at Goddard. "It was a wonderful surprise, of the kind we get in science sometimes."

Comets often brighten as they near the sun but tend to become lost in the glare when they approach too closely.

LASCO functions like a giant visor, blocking out the solar disc so observers can examine the surrounding area.

In all, Kracht has bagged 63 comets. The top hobby hunter is Michael Oates of Great Britain with 136.

"Until January 29, 2000, I had no idea that anyone could download images from a web site and make discoveries such as finding comets. The thrill of finding one is immense," Oates wrote on his Web site:

Comet competition

The SOHO science team sweetened the comet competition with a sweepstakes. Whoever came closest to predicting the day and time when the 500th SOHO comet made its nearest approach to the sun would win really cool prizes.

More than 1,200 people placed their bets between May 2 and May 31. The grand prize winner, Diane McElhiney, missed the so-called perihelion by only one hour and 43 minutes.

She earned a T-shirt, a poster with neat sun pictures and the DVD version of the IMAX film SOLARMAX. The score is by Nigel Westlake, the Australian composer best known for his soundtrack to the movie "Babe."

In the meantime, the comet search will go on, just for the joy of it. Participants caution that the enterprise can prove addictive, but it sure beats the conventional approach.

Xingming Zhou of China needed 15 years to discover one comet using a telescope. In the past two years, he found 13 while sifting through SOHO data.

SOHO orbits about 1 million miles (1.6 million kilometers) closer to the sun than the Earth in a so-called "Lagrange Point," where the gravity of the Earth and sun cancel each other out. The position gives the satellite an uninterrupted view of the sun.

For tips on how to hunt SOHO comets, visit:




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