Unlike earth, the moon has no atmosphere to protect it from space junk. On May 17 a boulder sized piece of that space junk slammed into the surface of the moon at almost 60,000 mph. Had you been looking at the moon when it happened, you would have seen the flash without a telescope. The impact was equal to the power of 5 tons of TNT. All from a boulder not much larger than a beach ball.
Since 2005 NASA has been monitoring “lunar impacts”, and report this one is by far the largest and brightest they’ve seen. They estimate the crater to be 20 meters across.