|Screenshot of meteor strike from video|
A boulder-sized meteor struck the Moon on March 17th, 2013, and the strike was visible to the naked eye despite the relatively small size of the object. The 40-kg (88 lbs) meteor measuring 0.3 to 0.4 meters (max 1.3 feet) wide slammed into the Mare Imbrium region of the Moon's surface while traveling at 56,000 mph, and scientists estimate the impact, which lasted for a second, glowed like a fourth magnitude star. Here's an explanatory video from Russia Today; the strike occurs at the 0:47 point, followed by a slo-mo instant replay:
The lack of an atmosphere ensured the meteor would not be slowed down or burned up upon entry. In response to the question as to how an explosion could take place in an oxygen-free environment, Bill Cooke of NASA's Meteoroid Environment Office said “Lunar meteors don't require oxygen or combustion to make themselves visible. They hit the ground with so much kinetic energy that even a pebble can make a crater several feet wide. The flash of light comes not from combustion but rather from the thermal glow of molten rock and hot vapors at the impact site”.
Amazing how the strike of an object little over one foot in diameter could generate an explosion on the Moon visible from Earth.