![]() ![]() That probe's measurements, Chen said, showed that the moon's far side, indeed, is incredibly quiet. Longijang 1, however, failed while entering the moon's orbit, so astronomers only received data from Longijang 2. The two spacecraft, also known as the "Discovering the Sky at Longest Wavelengths Pathfinder," rode to the moon with the Chang'e 4 mission that landed on the lunar surface in 2019. The mother spacecraft would then relay the measurements to Earth when crossing the moon's planet-facing side.Ĭhinese scientists have previously attempted to test this approach with two microsatellites called Longijang 1 and Longijang 2. The satellites would gather data while on the far side of the moon. China's constellation would achieve that in space, with the satellites circling the moon in the same orbit. ![]() Since radio waves are the type of electromagnetic radiation with the longest wavelengths, telescopes that can map their sources in the sky with high-enough resolution need to use multiple antennas distributed over a large area. Astronomers say that the moon's far side is, in fact, the most radio-quiet place in the whole solar system. During the lunar night, it also faces away from the sun, which, too, is a powerful source of radio waves. Far away from Earth's obstructive atmosphere, the moon's far side is also protected from man-made radio noise. The moon's far side, however, is probably the best place in the solar system to look for this mysterious signal. And that is exactly the type of electromagnetic radiation that cannot be seen from the planet's surface. ![]() As the redshift effect caused by the accelerating expansion of the universe stretches electromagnetic radiation from sources moving away from us toward longer wavelengths, what was microwave radiation emitted by the hydrogen atoms during the earliest epoch of the universe today appears to observers on Earth as long radio waves. Part of the microwave band of the electromagnetic spectrum, the 21 cm line has been helping astronomers track hydrogen clouds in our own galaxy, the Milky Way, since the 1950s, according to astronomer Ian Crawford of University College London.īut when searching for the 21 cm line from the earliest epoch of the universe, astronomers have to look for radiation with much longer wavelengths. Astronomers know, however, that this atomic hydrogen itself emits a type of signal known as the 21 centimeter line. Even when the first stars began to form, their light couldn't get through this haze at first. They think this type of radiation might allow them to peer into the so-called Dark Ages, the period of the first few hundred million years after the universe's birth in the Big Bang.Īt that time, the fledgling universe was filled with an impenetrable fog of hydrogen atoms. So we want to open this last electromagnetic window of the universe."Īstronomers are interested in this part of the electromagnetic spectrum for a good reason. "It's almost a blank part of the electromagnetic spectrum. "If you are looking into the low-frequency part of the electromagnetic spectrum, you'll find that, due to strong absorption, we know very little about below 30 megahertz," Chen said. A telescope on the moon, astronomers say, would allow them to finally see cosmic radiation in a part of the electromagnetic spectrum that is impossible to study from Earth's surface: radio waves longer than 33 feet (10 meters), or, in other words, those with frequencies below 30 megahertz (MHz). ![]()
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