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No bright comets are visible in our skies these nights, so this edition of "Comet Comments" contains no ephemerides or orbital elements. This gives us the opportunity to look back at 1999 and to discuss the comets we hope to see this year.
Amateurs Gary Hug and Graham Bell of Eskridge, Kansas, discovered a new comet on CCD images they took through a 0.3-meter Schmidt-Cassegrain reflector on December 10, 1999. The comet was magnitude 19 and near the Beehive cluster when found. Comet 1999 X1 (Hug-Bell) has a seven-year orbital period and stays outside the orbit of Mars.
The LINEAR program found its final comet of the year on December 20. Comet 1999 Y1 is more than a year from its perihelion, which is a distant 3.2 astronomical units.
Fifty-six comets were discovered in 1999. Only seven of them are periodic, returning in fewer than 200 years. Who made these discoveries? The LINEAR project in New Mexico, designed to find asteroids and comets that may hit the earth, found twenty. Many of these were first thought to be asteroids before closer examination (often by others) detected a coma or short tail.
The SOHO program found nineteen comets. SOHO is a spacecraft in solar orbit, about one million miles from Earth. It constantly monitors the solar region, and has taught us a great deal about the Sun. SOHO's comets are very bright and are often part of the Kruetz sungrazer family. Most of the SOHO comets are seen entering, but not exiting, the solar region. It is believed that they disintegrate as they pass near the Sun.
Australian amateurs Tillbrook, Lee, and Lynn visually discovered three comets. All three of their comets were found south of the equator.
Four other amateurs, in two teams of two, used their own CCDs to discover comets. Korlevic and Juric found a comet in February, while Hug and Bell found one in December.
The remaining twelve comets were found by those
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using professional equipment, often in the search for hit (or near-miss) asteroids and comets. Incidentally, for each comet discovered, hundreds of asteroids are found.
Although 2000 doesn't line up to be a great year for comets, you never know when a bright one will be discovered. Comet LINEAR (1999 S4) was expected to reach magnitude 3 by July (when it will be placed in the northern polar region); however, recent observations show the comet slow to brighten as it moves toward the Sun. During one stretch, dust production decreased rather than increased. Now the comet is 14th magnitude, and it will be interesting to see what happens before we lose it in the solar glare in early April. Comet McNaught-Hartley (1999 T1) may reach magnitude 6 late this year, but it is within 70 degrees of the Sun and far south until then. Finally, Periodic Comet Encke will be briefly visible from each hemisphere late in the year.
COMET HUNTING NOTES: The first visual telescopic comet discovery was made in 1680. In the 1760s, Charles Messier and others competed to visually discover new comets. The first photographic comet find was in the 1890s. For one hundred years, these were the two chief methods of finding comets. So what happened in 1999? Fifty six new comets were discovered: three were visual; two were photographic; and fifty-one were found by CCDs.
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