Page "Search for extraterrestrial intelligence" Paragraph 6

On August 21 – 23, 1924, Mars entered an opposition closer to Earth than any time in a century before or since.

In the United States, a " National Radio Silence Day " was promoted during a 36-hour period from the 21 – 23, with all radios quiet for five minutes on the hour, every hour.

At the United States Naval Observatory, a radio receiver was lifted 3 kilometers above the ground in a dirigible tuned to a wavelength between 8 and 9 kilometers, using a " radio-camera " developed by Amherst College and Charles Francis Jenkins.

The program was led by David Peck Todd with the military assistance of Admiral Edward W. Eberle ( Chief of Naval Operations ), with William F. Friedman ( chief cryptographer of the US Army ), assigned to translate any potential Martian messages.