Apr. 19, 2002 A new comet was discovered over the Internet by a Chinese amateur astronomer visiting the website for the Solar and Heliospheric Observatory (SOHO) spacecraft. The comet "C/2002 G3 (SOHO)" was first reported on Friday, April 12, by XingMing Zhou of BoLe city, in the XinJiang province of China, who discovered the comet while watching SOHO real-time images of the Sun on the Internet. The comet is a new comet, not belonging to any known group.
SOHO, launched over six years ago as a project of international cooperation between the European Space Agency (ESA) and NASA, has discovered more than 420 comets in just under six years. This makes the spacecraft the most prolific comet finder in the history of astronomy. Most of the comets were first spotted by amateurs around the world who downloaded SOHO's real-time images to their home computers. Anyone with Internet access can take part in the hunt for new comets and be a comet discoverer.
"From September 2000 to now I have been trying to find SOHO comets, and I've discovered 13 comets, one of which, designated '2001U9' and initially cataloged by the SOHO project as 'SOHO-367,' was the brightest one in the last two years," said Zhou, who previously spent more than 1,600 hours since his 1985 graduation scanning the heavens with his 15cm F/5.3 reflector telescope to discover a single comet.
"What's exciting about these near-sun comets is that we are exploring a population of comets that has never been seen before because they are very small and faint," said Douglas Biesecker, a solar physicist with L3 Com Analytics Corporation, Vienna, Va. "By the time their orbits take them close to the Sun so they become bright, they are lost in the Sun's glare and require a space-based coronagraph like that on SOHO to be seen." Biesecker, who is affiliated with the SOHO program at NASA's Goddard Space Flight Center in Greenbelt, Md., confirms potential comet discoveries as they are posted to the SOHO website.
C/2002 G3 (SOHO) will be visible in SOHO's Large Angle and Spectrometric Coronagraph (LASCO) C3 images until Saturday, April 20. The comet was first visible late in the day on Thursday, April 11. It entered the field of view at the bottom edge, almost directly under the Sun. It is moving upward to the left, and will eventually move back toward the right, exiting from the LASCO C3 field of view at the top edge, to the right of the Sun. First cataloged by the SOHO project as "SOHO-422," it has been officially designated C/2002 G3 (SOHO) by the International Astronomical Union.
The comet reached the point closest to the Sun in its orbit on April 17 at about 1:30 a.m. Eastern Daylight Time, at a distance of about 7.6 million miles (12.3 million kilometers). As the week goes on, the comet will move through the field of view more quickly.
In all these images, the shaded disk is a mask in the instrument that blots out direct sunlight, making faint comets and the dim outer atmosphere of the Sun, or the corona, visible. The white circle added within the disk shows the size and position of the visible Sun.
Solar radiation heats the comet, which in turn causes the outgassing of its water molecules and dust. The dust scatters sunlight at visible wavelengths, making the comet bright in LASCO images. The water molecules break down into oxygen and hydrogen atoms, and the hydrogen atoms interact with the coronal plasma (electrified gas that comprises the extended atmosphere of the Sun).
All the SOHO images are freely available on the SOHO web site: http://sohowww.nascom.nasa.gov/
More information about sun-grazing comets and how to spot new ones can be found at: http://sungrazer.nascom.nasa.gov/
Images and movies of the comet's passage are available at: http://soho.nascom.nasa.gov/hotshots/2002_04_15/
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