A member of a group of asteroids whose orbits cross that of the Earth. They are named after the first of their kind, Apollo, discovered in 1932 by German astronomer Karl Reinmuth and then lost until 1973. Apollo asteroids are so small and faint that they are difficult to see except when close to the Earth (Apollo is about 2 km across).

Apollo asteroids can collide with the Earth from time to time. Scientists estimate that several dozen asteroids 6 to 12 meters in size come near the Earth at a distance closer than the Moon. A collision with an Apollo asteroid 65 million years ago may have been one of the causes of the extinction of the dinosaurs. A closely related group, the Amor asteroids, come close to Earth but do not cross its orbit.