Eclipses cause strange effects on radio waves. An army of amateur broadcasters wants to know why

On his 7.25-acre parcel along a highway south of Indianapolis, Baker’s collection of spiky antennas pointing in various directions allows him to broadcast across the U.S. and far beyond. He has broadcast his voice to the other side of the world and held conversations with other amateur radio enthusiasts in Europe and even in New Zealand, 13,000 kilometers (8,000 miles) away.

One of the antennas in Baker’s yard is specially angled, he says, to transmit a radio signal that initially stays close to the ground. But eventually that signal will head into space. “When it hits the ionosphere,” Baker says, “it will jump. It will bounce.”

This phenomenon, in which radio waves are intentionally reflected from some of the upper layers of the atmosphere, greatly extends the distance over which radio operators can communicate. It’s called the “sky wave effect” and this is how The first radio transmission was sent across the Atlantic Ocean. in 1901.

It means that the curvature of the Earth can be overcome. Radio transmissions can zigzag up and down, bouncing between the ground and ionosphere, which is located at an altitude of approximately 80 to 650 kilometers (50 to 400 miles). You could say that a person’s voice, transmitted in the form of electromagnetic waves, literally touches the sky during long-distance transmissions that depend on this effect.

“The fact that you can pick up radio signals from the other side of the Earth,” says Cathryn Mitchell, professor of radio science at the University of Bath, “is really amazing.”

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The really surprising thing is that the effect of sky waves is not stable and scientists still do not fully understand it. He ionosphere is rare. It fluctuates, moves, expands and contracts, and is far from uniform. Sometimes it’s filled with waves, Mitchell says, which churn during sunrise and sunset, almost like throwing a rock into a pond.

The presence or absence of the Sun is one of the reasons for this. During the day, the ionosphere thickens because sunlight hits atmospheric gases, ionizing them to produce electrons. At night, collisions decrease and the lower layer of the ionosphere disappears. This nocturnal thinning allows radio waves to travel much further, because they reach higher altitudes before electrons bounce them back to Earth. That is why people have long been able to pick up distant radio stations in the first hours.