Near-Earth object the largest explosion in recorded history, equivalent to 20,000 megatons of TNT. It attracted widespread attention because it was discovered only after the closest approach. In March 1998, early orbit calculations for recently discovered asteroid showed a potential 2028 close approach from the Earth, well within the orbit of the Moon, but with a large error margin allowing for a direct hit. Further data allowed a revision of the 2028 approach distance to , with no chance of collision. By that time, inaccurate reports of a potential impact had caused a media storm. From the late 1990s, a typical frame
Near-Earth object smaller than about in diameter (i.e. H = 22.0 with assumed albedo of 14%), are not considered PHAs. NASA's catalog of near-Earth objects also includes the approach distances of asteroids and comets (expressed in lunar distances). The first near-Earth objects to be observed by humans were comets. Their extraterrestrial nature was recognised and confirmed only after Tycho Brahe tried to measure the distance of a comet through its parallax in 1577; and the periodicity of some comets was recognised in 1705, when Edmond Halley first published his orbit calculations for the returning object now known as Halley's Comet. The 1758–1759