Comets and Asteroids

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We don't usually think of Earth or Mars or the other worlds as "leftovers," but the Solar System has been pretty accurately described as "Jupiter plus debris." There is quite a lot of real junk left over from the formation of the Solar System floating around out there: comets and asteroids are a further area for the planetary enthusiast to explore.

Comets Every once in a while a spectacular comet visits the inner Solar System. After a comet drought that lasted over twenty years, we were treated to two "great" ones in the mid 1990s, Comet Hyakutake and Comet Hale Bopp. Another surprise came in 2007 when the normally sedate Comet Holmes (Plate 55) flared to brilliance and dominated northern hemisphere skies for weeks. The visit of a spectacular comet is a particularly exciting and busy time for both amateur and professional astronomers. We're in the spotlight, with the public looking to us for both views and information. Suddenly it seems as if everybody's interested in looking through the CAT. Even your formerly skeptical brother-in-law is no longer puzzled about why you spent all that money on a telescope.

Actually, an SCT is not required when a great comet is in full flower; a pair of binoculars or just a pair of eyes will do fine. An SCT can do a good job when the comet is dimmer, while approaching or moving away, and a telescope is required for the run-of-the mill comets that visit the inner Solar System every year. Most of these interlopers don't get much brighter than magnitude 8, and that makes them perfect candidates for viewing in an 8-inch or larger CAT. Some are fairly impressive, like the recent (2006) Comet Barnard, which showed a hint of a small tail as it drifted sedately through Hercules. Most comets are mere smudges, but all are interesting. Watch the astronomy magazines and the Internet for news of "good" comets. Spotting these little fellows can become a nice pastime.

Can anything help with dim comets? They are much like deep sky objects, and the tricks that work on the deep sky—averted vision, jiggling the telescope, etc.—

Plate 55. (Comet

Holmes) The sky is full of surprises, like Comet Holmes, which went from invisible to astounding in late 2007. Credit: Author.

work on them, too. How about light pollution reduction filters? Lumicon sells a filter formerly called the "Swan Band Filter," and now just called the "Comet Filter," that passes OIII and cometary "C2" lines. Does it work? On comets that display C2 emission (from diatomic carbon), it works pretty well. Unfortunately not all comets show this emission.

Asteroids Think Pluto is boring? Then you probably won't like asteroids, either. As the name implies, they look just like stars ("asters") in the eyepiece. The only sure means of identifying them, like Pluto, is by checking to see if they move against the background stars. Asteroids are inherently interesting because of what they are rather than how they look. They are the leftover pieces of a planet that was prevented from forming by the gravitational influence of mighty Jupiter. The area between Jupiter and Mars is littered with these chunks, which range from a few hundred kilometers to a few meters in size. Most interesting for the SCT user is the handful of relatively large and bright minor planets, with Ceres and Vesta being the best of the bunch. The prime attraction other than the "been there" factor is watching their motion against the stars.

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