Astronomers say they have observed a meteorite weighing almost half a tonne crashing into the Moon in September, creating a record-breaking impact visible on Earth.
The lunar impact produced an “extraordinary flash” which is the longest and brightest ever recorded on the Moon, the astronomers said.
The group, led by Prof Jose Madiedo, of the University of Huelva in south-western Spain, say the flash generated by the collision would have been so bright it would have been seen on Earth.
A video made by Prof Madiedo shows an afterglow that was visible for eight seconds after the rock smashed into an ancient lava-filled lunar basin called the Mare Nubium.
"At that moment I realised that I had seen a very rare and extraordinary event," he said.
"Usually lunar impacts have a very short duration - just a fraction of a second. But the impact we detected lasted over eight seconds. It was almost as bright as the Pole Star, which makes it the brightest impact event that we have recorded from Earth.”
Footage of the collision was captured on 11 September 2013 by two of the Moon Impacts Detection and Analysis System (Midas) project telescopes.
The Moon’s surface was hit by the rock travelling at 61,000km/h (38,000mph) which the team estimate would have weighed about 400kg (900lb). They said this would have released the energy equivalent of 15 tons of TNT, and may have excavated a new 40 metre-wide crater.
"Our telescopes will continue observing the moon as our meteor cameras monitor the Earth's atmosphere," Prof Madiedo said. "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."
The Spanish team believes one-metre objects may strike the Earth ten times more often than scientists previously thought.
Objects the size of the one that struck the moon's Mare Nubium usually burn up in the Earth's atmosphere, producing spectacular fireballs.
The study is published in the Monthly Notices of the Royal Astronomical Society.