The flash of light from the impact was so bright it would have been visible from Earth, they report in the current issue of the Monthly Notices of the Royal Astronomical Society.
"This is the largest, brightest impact we have ever observed on the moon," Jose Madiedo of the University of Huelva told the BBC. "The impact we detected lasted over eight seconds."
The Moon Impacts Detection and Analysis System of telescopes in southern Spain detected the explosive impact, with energy equivalent to around 15 tons of TNT, on Sep. 11, the researchers said.
"Usually lunar impacts have a very short duration -- just a fraction of a second," Madiedo said. "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."
They estimated the meteor, traveling at 38,000 mph, would have created a crater measuring around 130 feet across.