From year 2005 NASA astronomers have been monitoring the Moon for meteoroids landing on the lunar surface. "On March 17, 2013, an object about the size of a small boulder hit the lunar surface in Mare Imbrium," says 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."
On the impact the meteoroid travelling speed was 90,000 kph and weight 40 Kg, the explosion impact could be saw by anyone looking at the Moon with naked eye at that moment ( no telescope required ).
More informations at : http://science.nasa.gov/science-news/science-at-nasa/2013/16may_lunarimpact/