[meteorite-list] Catch Comet LINEAR Splitting in Two

[Ron Baalke]

http://skyandtelescope.com/observing/article_1531_1.asp

Catch Comet LINEAR Splitting in Two
By Edwin L. Aguirre
Sky & Telescope
June 17, 2005

The brightest comet in the sky right now isn't Tempel 1 or the fading
Machholz. It's one you've probably never heard of: Comet LINEAR, C/2005
K2, glowing at about magnitude 9.2 as of June 17th. It's visible with a
medium-sized telescope in the northwestern sky at the end of evening
twilight - but only for a few more days.

This minor comet recently brightened radically after going through a
dramatic change. Observers in Europe and the U.S. have obtained CCD
images that show what looks like its nucleus shedding a big fragment.
LINEAR's secondary nucleus appeared as a small, 17th-magnitude fuzzy
blob northeast of the primary, slowly drifting away in the direction of
the comet's short tail.

This breakup may have been the cause of C/2005 K2's ongoing outburst in
brightness; the comet brightened from magnitude 12 to 9 in the first
half of June. Typically, when a comet fragments, fresh icy material in
the nucleus's interior gets exposed to solar radiation, causing a
dramatic increase in the gas and dust output.

Comet discoverer and Sky & Telescope contributing editor David H. Levy
was comet hunting on the night of June 12th when he happened to sweep up
the (already-discovered) C/2005 K2 with a 10-inch telescope. "At 40
power, the object looked decidedly noncometary," noted Levy. "It was
unusually elongated; it appeared more like an amorphous,
low-surface-brightness galaxy than a comet, and that's what had me
fooled initially."

Comet on June 15th

Mike Holloway of Van Buren, Arkansas, captured the two images above on
June 12th at 3:27 UT and June 15th at 2:56 UT. They show the fragment
separating from the comet's main condensation during the 72-hour period.
Holloway used a 4-inch f/5.3 Takahashi refractor and an SBIG ST-2000XM
CCD camera. Photo by Mike Holloway.

C/2005 K2 is named after the LINEAR (Lincoln Near Earth Asteroid
Research) automated sky-survey program <http://www.ll.mit.edu/LINEAR/>
operating in Socorro, New Mexico, which discovered it on May 19th. It
was then only 19th magnitude. C/2005 K2 will reach perihelion on July
5th at about 0.54 astronomical unit (82 million kilometers) from the
Sun. This is the LINEAR project's 158th comet find.

Right now is the best time to try to spot the comet with a telescope,
before it gets too low in twilight. As of June 15th it's in Lynx about
30° above the northwestern horizon after dusk for observers at 40° north
latitude. It's rapidly heading south and dropping lower daily; it will
be in poor view by the 22nd. Use the ephemeris below to plot the comet's
position on a detailed star chart such as Sky Atlas 2000.0 or
Uranometria 2000.0 If you have sky-map software on your computer, you
can get orbital elements (or coordinates) from the Minor Planet Center
<http://cfa-www.harvard.edu/iau/MPEph/MPEph.html> and plot the comet's
course yourself.

Comets break up fairly often due to structural weaknesses in their
nuclei. Solar heating, for instance, can cause pockets of volatile ices
to sublimate rapidly, inducing stresses in the nucleus. Some famous
examples include Comet West, which split into four pieces after
perihelion in 1976, and Comet Shoemaker-Levy 9, which broke apart due to
tidal forces during a close approach to Jupiter prior to its discovery
in 1993. That comet's 21 sizable fragments returned to Jupiter and
crashed into the planet the following year.

Here are the right ascension and declination of C/2005 K2 at 0:00
Universal Time (which falls on the evening of the previous date in North
America):

Comet Positions
Date (0h UT) R. A. Decl.
June 16 8h 48.2m +39° 38'
June 17 8h 48.3m +36° 39'
June 18 8h 48.3m +33° 44'
June 19 8h 48.1m +30° 54'
June 20 8h 47.7m +28° 10'
June 21 8h 47.2m +25° 31'
June 22 8h 46.5m +22° 59'