A car-sized asteroid smashed into the moon last year and left the longest-ever afterglow for a lunar impact ever seen—one big enough to be spotted by the naked eye under good viewing conditions, a Spanish astronomer said Monday. Jose Maria Madiedo said he witnessed the blast while working two lunar-observing telescopes on September 11, AFP reports. "At that moment, I realized that I had seen a very rare and extraordinary event," he said. The 8-second afterglow was for a brief moment as bright as the Pole Star in the northern hemisphere, British scientists said.
The asteroid weighed about 880 pounds, measured up to 4.5 feet in diameter, struck at roughly 56,000mph, and caused a blast equivalent to 15 tons of TNT—making it three times bigger than any other such recorded hit on the moon, Space.com reports. Similar asteroids hit Earth more commonly than previously believed, but our atmosphere burns them up into so-called "fireball" meteors; on the moon, it's just a direct hit. NASA has seen more than 300 meteors hit the lunar surface since 2005, and plans to keep watching. "In this way we expect to identify clusters of rocks that could give rise to common impact events on both planetary bodies," Madiedo said. "We also want to find out where the impacting bodies come from." (Read more asteroid stories.)