How does a laser beam measure the distance to the Moon so accurately? © Getty Images

How does a laser beam measure the distance to the Moon so accurately?

It's a long trip to the Moon, but thanks to early space explorers we know exactly how far.

Asked by: Colin Gray, Castle Cary

Advertisement

In 1969, the Apollo 11 astronauts placed the first of four mirrors on the Moon that reflect back laser beams to reveal the distance to the Earth. The beams travel at the speed of light and their journey times are measured to within a few million-millionths of a second, the distance can be recorded to within a few millimetres.


Advertisement

Subscribe to BBC Focus magazine for fascinating new Q&As every month and follow @sciencefocusQA on Twitter for your daily dose of fun science facts.