On March 6th and 7th, 2006, the near-Earth asteroid 2000 PN9 (also known as asteroid number 23187) will be flying by Earth, missing us by 2 million miles in the northern sky. The asteroid will be 12th magnitude those evenings as it races across the sky; users of 4- or 6-inch and larger telescopes should be able to see it creeping against the background stars — if they know exactly where to look. On March 8th it will be faded to magnitude 12½; on March 9th and 10th it will be magnitude 13.

To get an ephemeris (listing) of the asteroid's positions, for plotting on a highly detailed star atlas, use the JPL's HORIZONS system. The asteroid is so close that its apparent position will depend somewhat on your location on Earth, so in "Observer Location" enter a city near you. In "Time Span" choose a step value of 1 hour and enough steps to cover the nights you want. Then click "Generate Ephemeris." The times and dates in the output are in Universal Time. (To change this to Eastern Standard Time, subtract 5 hours.)

About Alan MacRobert

Alan M. MacRobert became an avid Sky & Telescope subscriber in 1966 at age 14, joined the editorial staff in 1982, and is now a senior contributing editor, semi-retired. He played a role in practically every part of the magazine and the company's other products for more than a generation, both on the amateur-observing side and the science-reporting side. In 1994 a book collection of his observing how-tos and telescopic sky tours was published as Star Hopping for Backyard Astronomers. He has produced This Week's Sky at a Glance online every week since 1989.

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