On New Year’s Day, 1801, the Italian astronomer Giuseppe Piazzi discovered a new “planet” between the orbits of Mars and Jupiter. It was much smaller and fainter than the other known planets, so it was called a minor planet or asteroid (from its starlike appearance). Since then, several hundred thousand asteroids have been discovered and catalogued, and thousands more are discovered each year.
Most of the asteroids in the main asteroid belt remain there, but some have highly eccentric orbits that take them out of the belt and across the orbital path of the Earth, as well as the paths of other terrestrial planets. These asteroids are called Near Earth Objects, or NEO’s, and pose potential threats to the Earth.
On November 8, 2011, Near Earth Asteroid 2005 YU55 will pass within 0.85 lunar distances from our planet, and although this is the largest asteroid to swing past us for the next 17 years, YU55 is not an immediate threat to the Earth. It will miss us by a comfortable margin of 200,000 miles (325,000 kilometers).
2005 YU55 was discovered on December 28, 2005, by Robert McMillan of the Spacewatch Program. It is a nearly spherical object about 1,300 feet (400 meters) in diameter and is classified as C-type. Asteroids of this type are the most common variety and are usually found in the outer regions of the asteroid belt. They have very dark and neutral-colored surfaces, and are probably of carbonaceous composition similar to primitive carbonaceous chondritic meteorites.
2005 YU55 will make its closest approach to Earth on November 8th at 23:28 UT (6:28 P.M. EST). The best time for observing will be a few hours later, late in the day on November 8th and early on November 9th. The asteroid should reach about 11th magnitude for several hours before it fades as its distance rapidly increases.
Observations will be complicated by the asteroid’s rapid motion across the sky. If you want to track 2005 YU55 with your telescope, you will need accurate finder charts, for your specific location on Earth. With planetarium software such as SkyChart 3 and a good printer you can create high quality custom finder charts on your own.