Ask the Astronomer
Astronomer William Georgevich replies:
Comets hitting the Earth is the other favorite topic for sci-fi writers to hypothesize about. The best book about a comet hitting the Earth is Luciferís Hammer, which accurately describes how a comet might split into pieces as it enters the Earthís atmosphere destroying different parts of the Earth. Fortunately a devastation of that nature is expected once every 60 million years. Scientists say we are about due but even a 1% error on this estimate means all of us have a give and take of at least 600,000 years - a margin of safety I feel very comfortable with.
There is no best time of year to look for comets. In fact, there is no best place to look either. Master comet discoverer David Levy (of Comet Shoemaker-Levy fame) told me he scans the sky systematically, especially the early morning sky just before dawn, because each succeeding night a little more of the Universe unexamined by comet hunters is exposed for view looking East. I personally find it amazing that comets are so often discovered simultaneously within a few hours of each other considering how difficult they are to find.