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1998 WT24 Sails by the Earth
1998 WT24 Sails by the Earth
11 Dec 2001
(Source: Sky & Telescope)

Roger W. Sinnott
Sky & Telescope

On Saturday night, December 15-16, the minor planet 1998 WT24 passes within five Earth-Moon distances of our planet on an inward journey toward the Sun. For a few nights around that time, the asteroid will be bright enough to spot easily in 4-inch and larger telescopes as it races across the constellations Gemini, Auriga, and Perseus toward Andromeda. Since it will be moving up to 1 degree per hour, skywatchers might actually be able to perceive its motion directly with a high-power eyepiece whenever the asteroid goes near a background star.

A fine opportunity for observers in the Americas to identify 1998 WT24 comes on Saturday morning, December 15th, when it glides through the northern fringe of the bright open cluster M38 in Auriga. This takes place near 8:20 Universal Time (that is, 3:20 a.m. EST or 12:20 a.m. PST). The asteroid will then be at its brightest, about magnitude 9.5.

Planetary scientist Steve Ostro (Jet Propulsion Laboratory) says that extensive radar imaging of 1998 WT24 is scheduled for the radio telescopes at Goldstone, California, and Arecibo, Puerto Rico, during the flyby. Discovered three years ago, 1998 WT24 is a kilometer-size body that completes an orbit around the Sun in only about seven months. That puts it in the elite Aten class of asteroids.

On December 10th, Petr Pravec and Lenka Sarounova (Ondrejov Observatory) told members of the Minor Planet Mailing List (MPML) that their latest light curve suggests this object rotates in about 3 hours. Its light fluctuates by about 0.24 magnitude. But the weather forecast is not favorable for the Czech Republic, and they urge other photometric observers to confirm their results during this very favorable opportunity. (For information on subscribing to the MPML, visit

The table below gives 1998 WT24's right ascension and declination (equinox 2000.0) at the start of each hour UT during the December 14-17 close approach, along with its predicted visual magnitude and motion in arcseconds per minute. These predictions are from the Minor Planet Ephemeris Service of the Minor Planet Center in Cambridge, Massachusetts ( Keep in mind that these are geocentric positions. Because the asteroid is passing so close to the Earth, parallax at a particular observing site could displace it by as much as 10 arcminutes or so.

Roger W. Sinnott
Senior Editor
Sky & Telescope magazine

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Last Updated: 12 Dec 2001