The Moon as a unique radio astronomy platform and Chang’e 4

The side of the Moon that never faces the Earth, the lunar farside, is uniquely placed for radio observations of the Universe.

An artist’s impression of radio telescopes on the Moon’s farside. Source: NASA

There are hundreds of radio telescopes on Earth, some of which helped produce the recent black hole image, then why do radio astronomy on the Moon? Well, human activity on Earth contributes a lot of noise to radio observations. Since the farside of the Moon never faces the Earth (due to tidal locking), it is shielded from Earth’s radio interference. Moreover, the Earth’s ionosphere blocks very long wavelength (i.e. low-frequency) radio waves from coming through. These are accessible from the Moon. Plenty of craters, big and small, and the Moon’s low gravity allow for large radio dishes to be built relatively easily (assuming we have colonized the Moon :P)

The combination of low radio noise, access to unique radio frequencies and natural topography make the Moon an excellent place for unique science. Prime scientific targets include the early Dark-Universe from before stars were born, structures of galaxies and galaxy clusters, nature of radio bursts from cosmic rays hitting the lunar surface, and even observation of radio emissions from exoplanets!

As I write this, low-frequency radio observations are happening on the Moon. Chinese Chang’e 4, the first spacecraft to land on the lunar farside, is using its three 5-meter antennae to create a high-resolution radio map of the sky. Chang’e 4 radio observations will demonstrate the potential of radio astronomy on the Moon. Expected results include insights into cosmology, solar radio bursts and even planetary observations.

It will be exciting to see future lunar colonies with large, Arecibo style radio dishes built on craters peeking at the radio sky. Better yet, an array of radio dishes on the Moon will allow large-scale interferometry with telescopes on Earth. Interferometry is the same technique that produced the first black hole image. Such increase in the baseline size (Earth-Moon distance!) will result in higher resolution images of black holes and other objects of interest. There’s a lot of potential for radio astronomy from the Moon. And all of it is a bonus to having a sustainable presence on the Moon and beyond.

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