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The Long and Short of a Comet

July 24, 2000

Comets are chunks of ice, gravel, dust and rock stuck together in a lumpy ball. They orbit the Sun on lots of differently shaped paths; some are almost circular, traveling far from the Sun, and others have incredibly elongated orbits which take them deep into the inner solar system for a brief time before heading back out into the depths of space.

Not all comets are as spectacular as Hale-Bopp or Hyakutake, which were naked-eye objects in the late 1990s. Comet 1999 S4 LINEAR, which came swinging by in mid-2000, never got quite bright enough to see with the naked eye, but made a fine sight in binoculars or a small telescope. It was the brightest comet since the two mentioned above, so it got a small amount of media attention.

One such attentive medium was the San Francisco Chronicle. They commonly cover astronomical events, which is wonderful. However, like all things human, they sometimes make mistakes. On July 20, 2000, they had a brief report about comet LINEAR. They said

The Linear comet is believed to have been launched on its 100-year voyage around
the sun from a huge cloud of similar objects that surrounds the solar system more than a trillion miles away.

A minor point is that LINEAR is an acronym for ``Lincoln Near-Earth Asteroid Research'', and so it should be in all capital letters. A more important point is that the comet's period is longer than 100 years; much much longer. Although an exact figure is difficult to find, one approximation yields a period of 14 million years. The far point in its orbit is over 100,000 times farther from the Sun that the Earth ever gets, and it takes a long time to move that far. If you miss S4 LINEAR this time, don't wait up to see it again.

More info about 1999 S4 LINEAR and other comets can be found at Gary Kronk's wonderful Comets and Meteor Showers website. You can try to observe it yourself, too. Maps can be found at the Heavens Above website (you'll have to know your latitude and longitude for that).

My thanks to regular Bad Reader Andrew Lloyd for this one!

©2008 Phil Plait. All Rights Reserved.

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