Scientists at NASA's Near-Earth Object Program, which tracks asteroids and comets, ruled out any chance of impact. They're using the close encounter to learn more about the space rock known as 2005 YU55.
The last time a cosmic interloper this size came this close to Earth was in 1976 and it won't happen again until 2028.
Since late last week, antennas at the space agency's Deep Space Network in California have been monitoring the quarter-mile-wide asteroid as it approaches from the direction of the sun.
The Arecibo Observatory in Puerto Rico planned a viewing Tuesday when the asteroid is set to make its closest pass at a distance of 202,000 miles at 6:28 p.m. EST.
Researchers will analyze radar images to glean details about the asteroid's surface features and shape.
Since its discovery six years ago by a University of Arizona astronomer, scientists have learned a great deal about 2005 YU55. Its surface is coal black, and it spins slowly through space.
Amateur skygazers who want a glimpse need two things: a good sky chart and a 6-inch telescope or larger since the asteroid is too faint to detect with the naked eye. Even with a telescope, sighting is not guaranteed. The glare from the moon may make the asteroid difficult to spot.