Today in History—February 27: The Discovery of Solar Radio Waves

On this day in 1942 a British physicist made a monumental discovery…and couldn’t tell anyone.

British radar equipment operating at 55–85 MHz was experiencing severe interference: strange, powerful signals that jammed their systems. This was the middle of World War II, so everyone assumed that the Germans had found a way to scramble British defense communications.

They weren’t entirely wrong. Radio jamming was already part of the conflict, an invisible battle being fought across the airwaves. By flooding the frequencies, enemy signals could disrupt radar, leaving a target blind and vulnerable to attack.

Radar itself was still something of a marvel. Radio waves had only been detected decades earlier, and radio signals from space were barely understood. These waves—part of the same electromagnetic spectrum as ultraviolet light and X-rays—could be sent out to bounce off distant objects and return with information.

In wartime, whoever controlled the signals controlled what could—and couldn’t—be seen.

James Stanley Hey was tasked with improving that system for the British. The physicist had joined the Army Operational Research Group, where he was assigned to study and refine radar for antiaircraft guns.

That February, reports of radar interference surged. But the pattern didn’t match enemy action. Hey noticed that the jamming began at sunrise and ended at sunset. Astronomers at London’s Royal Observatory confirmed that a massive sunspot was working its way across the Sun’s surface. Hey knew that sunspots were sources of strong magnetic activity—and he began to suspect a very different “enemy”: the Sun.

The interference was indeed being caused by solar radio bursts: intense emissions of electromagnetic radiation that could overwhelm certain radio frequencies. In identifying this, Hey had accidentally discovered that the Sun itself produces radio waves.

He couldn’t publish his findings in the middle of a war. In 1946, after the conflict ended, Hey confirmed that bursts of solar radio waves coincided with solar flares. It was the accidental birth of solar radio astronomy.

It turned out that the Sun had been broadcasting all along. We just weren’t listening.