(CNN) -- A meteoroid struck the surface of the moon recently, causing an explosion that was visible on Earth without the aid of a telescope, NASA reported Friday. But don't be alarmed if you didn't see it; it only lasted about a second.
"It exploded in a flash nearly 10 times as bright as anything we've ever seen before," said Bill Cooke, of NASA's Meteoroid Environment Office.
NASA astronomers have been monitoring the moon for the past eight years, looking for explosions caused by meteoroids hitting the lunar surface. It's part of a program to find new fields of space debris that could hit Earth. NASA says it sees hundreds of detectable lunar meteoroid impacts a year.
None however can match the size of the explosion they say they saw March 17. NASA says the meteoroid was about 40 kilograms and less than a meter wide, and it hit the moon's surface at 56,000 mph. It glowed like a 4th magnitude star, NASA says, thanks to an explosion equivalent to 5 tons of TNT.
"It jumped right out at me, it was so bright," said Ron Suggs of the Marshall Space Flight Center.
Cooke says Earth was pelted by meteoroids at about the same time, but they hit the moon because it has no atmosphere to protect it.
"We'll be keeping an eye out for signs of a repeat performance next year when the Earth-moon system passes through the same region of space," Cooke said.
If you're wondering how there can be an explosion on the moon, without oxygen, NASA has the answer for you. It says the flash of light comes not from any type of combustion -- as we typically think of explosions -- but rather by the glowing molten rock at the impact site.

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