"School kids measure distance to the Moon":

The students analysed an mp3 recording of the conversation between Neil Armstrong on the surface and ground control in Houston in which he utters his famous "one small step" speech. The recording is available on the NASA website.

They noticed an echo on this recording in which sentences from Earth are retransmitted via Armstrong's helmet speaker through his microphone and back to Earth. They used the open source audio editing program Audacity to measure the echo's delay which turned out to be 2.620 secs and used this to work out the distance to the moon as 3.93 x 10^8 metres.

That's not bad given that the actual distance varies between 3.63 and 4.05 x10^8 metres.