Astronomers will observe a newly discovered asteroid on Jan. 27-28 and Feb 1-4, 2008, as the object called 2007 TU24 passes within 1.4 lunar distances, or 334,000 miles, from Earth. The asteroid, estimated at between 150 and 600 meters in diameter — about 500 feet to 1,900 feet, or the size of a football field, at 360 feet, to the size of Chicago’s 110-story Sears Tower, at 1,454 feet — was discovered in October 2007. It poses no threat to Earth, but its near approach gives astronomers a golden opportunity to learn more about potentially hazardous near-Earth objects.