High Quality Content by WIKIPEDIA articles! 2005 YU55, also written as 2005 YU55, is a potentially hazardous asteroid 310 meters or about 400 m (1,300 feet) in diameter. It was discovered on 28 December 2005 by Robert S. McMillan at Steward Observatory, Kitt Peak. On 8 November 2011 it passed 0.85 lunar distances (324,900 kilometers; 201,900 miles) from the Earth. This is the closest known approach by an asteroid with an absolute magnitude this bright since 2010 XC15 (H = 21.4) approached within 0.5 lunar distances in 1976.