How do We Know the Distance to the Moon? To the Planets?

Today in History, January 10, 1946:

“Operation Diana”.

The US Army Signal Corps, using a “bedspring antenna” radar from a World War II era US Navy ship, somewhat modified, bounces a signal off of the moon, which took 2.5 seconds to return to the Earth.

The experiment was the precursor to using Radar to determine the distance to other bodies, such as Saturn, and for learning to communicate with later spacecraft outside of Earth’s atmosphere.

Diana was the Roman Moon Goddess, and this project would take the lead in naming later space projects after Roman Gods.