A Spanish astronomer spotted an asteroid the size of a small car crashing into the moon, it has been revealed.
Jose Madiedo, a professor at the University of Huelva, witnessed the 400kg meteorite hurtling through space at a speed of 61,000km/h into the lunar surface. It was the largest moon impact ever recorded.
Details about the rare sighting of the asteroid, which was as bright as the Pole Star, have only just been published by the Royal Astronomical Society.
Anyone on Earth looking at the moon at that time of the collision in September would have spotted it with the naked eye. The crash produced an eight-second afterglow before the meteorite vaporised, the society added.
Madiedo, who was operating two telescopes in search of such unusual sightings, said: "At that moment I realised that I had seen a very rare and extraordinary event."
The impact of the collision created a 40-metre-wide crater and released energy equivalent to an explosion of 15 tonnes of TNT.
A society spokesman said: "Our telescopes will continue observing the moon as our meteor cameras monitor the Earth's atmosphere. In this way we expect to identify clusters of rocks that could give rise to common impact events on both planetary bodies. We also want to find out where the impacting bodies come from."
Spanish scientists concluded that metre-sized objects may strike Earth up to 10 times more often than previously believed. The atmosphere often creates spectacular "fireball' meteors".