For nearly as long as there has been radio, there have been antennas trained on the sky, looking at the universe in a different light than traditional astronomy. Radio astronomers have used their sensitive equipment to study the Sun, the planets, distant galaxies, and strange objects from the very edge of the universe, like pulsars and quasars. Even the earliest moments of the universe have been explored, a portrait in microwave radiation of the remnants of the Big Bang.
And yet with all these observations, there’s a substantial slice of the radio spectrum that remains largely a mystery to radio astronomers. Thanks to our planet’s ionosphere, most of the signals below 30 MHz aren’t observable by ground-based radio telescopes. But now, thanks to an opportunity afforded by China’s ambitious lunar exploration program, humanity is now listening to more of what the universe is saying, and it’s doing so from a new vantage point: the far side of the moon.
Bouncing Both Ways
As any amateur radio operator can tell you, the key to direct global radio communication is the Earth’s ionosphere – those layers of charged particles that ebb and flow 50 to 600 miles (80 to 1000 km) above our heads. Produced by the constant stream of radiation flowing from the Sun and interacting with the Earth’s magnetic field, the ionosphere has long been known to refract radio waves. The degree to which radio waves are refracted depends on things like the structure of the ionosphere, which changes diurnally, as well as the angle at which the radio waves strike the charged particle layers. But refraction also depends heavily on the wavelength of the incident waves, with the 10-meter band, or 28 MHz, normally considered the upper limit for useful ionospheric bounce.
The refrac ..
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