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Treebeard's Stumper Answer
31 Jan 97

A new comet is coming! Comet Hyakutake made a great show last year. Comet Hale-Bopp (named after its discoverers) promises to be even brighter later this spring. It is currently a faint morning star, visible (with binoculars) low in the East just before sunrise. But before Christmas, it was an evening star, visible low in the West just after sunset. How can this comet jump from one side of the night to the other in just a month? Comets are fast, but not that fast!

Comet Hale-Bopp was an evening star before Christmas, but now it's a morning star. This happened because the comet went around the Sun. Imagine the comet approaching the sun. The sun sets (because the Earth turns), and we see the comet for a short time before it also sets. When it emerges on the other side of the sun, it sets first, so we don't see it then. But now it's a bit ahead of the sun, so we get a glimpse of it in the morning. This is a small change for the comet, but it makes a big change in when we see it.

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Marc Kummel / mkummel@rain.org