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

More information about sun-grazing comets and how to spot new
ones can be found at:
Images and movies of the comet’s passage are available at: