National Radio Silence Day

Summary

In August 1924, as Mars passed within about 56 million kilometres of Earth, the retired Amherst astronomer David Todd urged the world's radio stations to fall silent so that any signals from Mars could be heard. A few stations went quiet for minutes at a time, the US Army and Navy listened, and nothing from Mars was received.

Later retellings give the episode a name, National Radio Silence Day. The newspapers of that week record no such day. They describe a proposal, a patchwork of brief and mostly voluntary silences, a Navy that declined to silence its stations, and a strip of film whose maker did not think it came from Mars.

What is documented

The approach. Late on 22 August 1924 (Universal Time), Mars made its closest approach to Earth of that opposition, at about 0.3728 astronomical units, or 55.8 million kilometres, according to NASA's JPL Horizons ephemeris. The Washington Evening Star told its readers that day that the planet was "a mere 34,000,000 miles away".

The proposal. At the end of July 1924 David Todd, emeritus professor of astronomy at Amherst College, proposed that all the radio stations in the United States but one cease sending on a night shortly before 22 August, and that all sending then cease while the world listened for a response from Mars. He also suggested sending the airship Shenandoah up 10,000 feet on 22 August so that its radio operators could listen. He was reported as saying: "Not for five centuries will there be another opportunity physically as favorable." JPL's ephemeris puts Mars slightly closer to Earth in August 2003, 79 years later.

The response. On 21 August the Evening Star reported that "The Navy Department is frankly skeptical and has declined to silence its stations", while the War Department had "ordered operators to keep quiet a few minutes each day". Washington's two long-distance broadcasters, WRC and WCAP, had received no request to keep silent. Todd said that day that his plan, if carried into effect, would be "a pure gamble". The chief of naval operations, Admiral Edward W. Eberle, ordered 20 of the Navy's most powerful shore stations to listen for signals from Mars from midnight on 21 August until 8 am on Monday 25 August, and the War Department gave Army stations a similar order. On the evening of 22 August WRC announced that it would stay silent for five minutes in every hour, beginning at the fiftieth minute, and that it would do the same the next night. In Argentina the high-power station at Monte Grande suspended transmitting for ten minutes in each hour, for four hours from midnight on the Thursday. The request there was said to have come from the Argentine ambassador in Washington, Honorio Pueyrredón, who indicated, according to the report, that Todd's idea had been approved by all the American government departments.

What was heard. Operators of a railway receiving set at Norfolk, Virginia, reported signals "not in any known code". From Vancouver came reports of combinations of four dashes, at first taken for messages from Mars. On 23 August E. J. Haughton, superintendent of the Dominion government wireless service, explained them: they had been heard every morning for four weeks, and were "merely those sent from United States radio beacons", which guided vessels in Puget Sound and on the Columbia River.

The film. C. Francis Jenkins, the Washington inventor of a method of transmitting photographs by radio, set up an automatic recorder in his laboratory to catch any unusual signals. It was tuned to a wavelength so long, the Washington Daily News reported, that it would cut out any earthly station, and it traced what it received as a line on photographic film. On 27 August the same paper described a film developed the day before. Near its start was "a dot and dash effect". On the other side were "a series of waved marks, occurring with a frequency of every seven and one-half minutes", before and after "a peculiar, intricate series of marks closely resembling the face of a man". Reception had been on wavelengths of 5,000 to 6,000 metres. Jenkins handed the film to the Navy's code experts. The paper reported that Todd was "elated" and that Jenkins "scouts the theory that it may have resulted from an attempt by Mars to communicate with the earth".

Todd's position. In November 1924 a syndicated feature on Todd reported that the "Mars messages" received in the Washington laboratory would not be accepted as authentic until terrestrial disturbances had been checked and all radio reception between 24 July and 24 September surveyed. The registry has found no report of that survey's result.

Leading explanations

Terrestrial transmitters (established for the one signal that was traced). The Vancouver dashes were identified within a day as United States radio beacons. The other signals reported that week were not assigned a source in the reports the registry consulted.

Signals from Mars (Todd's hope; unsupported). Nothing received in 1924 was shown to come from Mars. The film offered as the best evidence was not attributed to Mars by the inventor who recorded it, and Todd himself treated the "messages" as unauthenticated.

A new radio phenomenon (Jenkins's suggestion; untested). The Washington Daily News reported that Jenkins leaned "to the idea he may be on the threshold of a new radio discovery". No such discovery is recorded in the sources consulted.

Current status

Debunked. Mars came close in August 1924; Todd asked for silence; a few stations briefly gave it; the Army and Navy listened; and nothing from Mars was received. The one signal that was traced came from radio beacons, and the film was not claimed as Martian by its maker. No national radio silence day, and no national order for one, appears in the contemporary reports the registry read. A 1924 source describing such an order would change that finding. Nothing in the record suggests that anything was received from Mars.

Last reviewed: September 2026. Records are provisional. Where the evidence changes, the entry changes. Found an error? Tell us.