Late Sunday night — that is, in the predawn hours of Monday, July 3, 2006 — a small asteroid will sail from Andromeda past the Double Cluster in Perseus, then through Cassiopeia and into Cepheus. For a few hours it will be as bright as 11th magnitude, making it easily visible to skywatchers with a 6-inch telescope or larger. North America happens to be the best place on Earth for witnessing this event in a dark sky.
To help skywatchers locate the asteroid, dubbed 2004 XP14, we’ve prepared three detailed, overlapping star maps: Chart A, Chart B, and Chart C. (Click on the names in the caption above) Each is an Adobe PDF file that you can print for use at the telescope. Because the path shown extends more than 33° across the star-rich Milky Way, it wasn’t practical for us to include stars fainter than magnitude 10.0. The asteroid is somewhat fainter than this limit, but its obvious motion in the eyepiece field will be a dead giveaway that you're looking right at it. At its fastest, between 4:00 and 5:00 Universal Time, it will be traveling the Moon’s angular diameter every 4 minutes.
The asteroid is passing so close that its track you see it take against the background stars will depend somewhat on your location on Earth (the "topocentric parallax" effect). Be sure to pick the track for the city nearest you, or mentally interpolate between two cities.
In all cases the small crosses on the tracks show the asteroid’s location at 10-minute intervals of Universal Time. These predictions are based on orbital data from the Minor Planet Center in Cambridge, Massachusetts. Tracks are plotted only when the asteroid is at least 10° above the horizon and the Sun is still at least 10° below the horizon (mid-dawn).
The best strategy, as I learned when following a similar object with a 6-inch telescope in 2002, is to identify a star on one of our charts that the asteroid will pass very close to as seen from your location. Set the telescope on this star a few minutes ahead of the encounter time indicated by our chart, then simply watch and wait. Presently you’ll spot a tiny point of light gliding perceptibly past the star!
This asteroid was first picked up in December 2004 by the LINEAR survey program in Socorro, New Mexico. It is believed to be about 800 meters (a half mile) in diameter. At the time it was much fainter (magnitude 19) and farther away from Earth, but the character of its orbit caused astronomers to classify it as a PHA (potentially hazardous asteroid). The current flyby is only moderately close, the minimum distance being somewhat greater than that of the Moon. Still, this is by far the closest that this particular object will come during the rest of the 21st century.