Moon explosion: NASA says Huge explosion on the Moon visible to Earth. Meteoroid has smashed into the Moon, causing the biggest explosion ever seen on the lunar surface which was visible from Earth with the naked-eye, NASA said. "On March 17, 2013, an object about the size of a small boulder hit the lunar surface in Mare Imbrium," said Bill Cooke of NASA's Meteoroid Environment Office. "It exploded in a flash nearly 10 times as bright as anything we've ever seen before," said Cooke. Anyone looking at the Moon at the moment of impact could have seen the explosion - no telescope was required. For about one second, the impact site was glowing like a 4th magnitude star, researchers said. Ron Suggs, an analyst at the Marshall Space Flight Center, was the first to notice the impact in a digital video recorded by one of the monitoring program's 14-inch telescopes, said NASA. "It jumped right out at me, it was so bright," he said.