School kids measure distance to the Moon

Last week, four Spanish students revealed how they had taken pictures of the curvature of the Earth by attaching a digital camera to a helium balloon and letting it go. When the British newspaper The Daily Telegraph reported the work, the story snowballed, attracting worldwide coverage.

Now a group of 30 Italian students from classes 1SD and 1SE at the Liceo Scientifico “A. Vallisneri” in Lucca, Italy have gone one better with an ingenious measurement of the 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.

The students then went on to measure the eccentricity of the moon’s orbit using conversations recorded during the Apollo 17 mission, which was on the lunar surface for 300 hours.

They even estimated their errors using the Moon’s ephemerides. Likely errors include delays caused by electronics and the time it took for the signals to be routed to the various antennae around the world that NASA used for communications.

Not bad for a group of 14-19 year olds.

Ref: arxiv.org/abs/0903.3367: Echoes From The Moon