For many years, astronomers have mused about the possibility of putting radio telescopes on the Moon. Considering the extreme temperature variations, high levels of solar radiation (our atmosphere protects us), fine abrasive dust that gets into everything, and of course the logistical difficulties—why would we want to do that?
Radio astronomy is the study of naturally occurring radio emissions from space. Despite the enormous power radiated by most cosmic radio sources, their huge distances from us mean that by the time these radio emissions reach us, they are incredibly weak. If an optimistic astronaut were standing on the lunar surface trying to use their cell phone, the signal reaching us here on Earth would be stronger than the signals reaching us from any of those cosmic radio sources—possibly with the exception of the Sun when it is particularly active. Since all the cell phones operating around us are a lot closer than the Moon, we have to protect our radio telescopes from them—and also from the cacophony of other radio signals we use in our daily lives.
However, even in the increasingly radio-polluted environment here on Earth, radio astronomy remains possible for three main reasons. Firstly, we put our radio telescopes in remote locations or, as in the case of our observatory, in a sparsely populated basin surrounded by hills that block out most interference. Secondly, under an international treaty managed by the UN, every human activity involving radio waves—like radio broadcasting, TV, WiFi, Bluetooth, etc.—is allocated specific frequency bands. There are frequency bands allocated for radio astronomical use too, providing a good degree of protection from interference. Finally, we are developing better devices for detecting, identifying, and—when possible—mitigating interference.
One of the main ways we have avoided interference from devices moving around on the ground is that we generally point our radio telescopes at the sky. Until recently, apart from the odd bit of interference from spacecraft with defective electronics and occasional interference from aircraft, this worked. Now things are changing dramatically.
In order to provide reliable Internet access worldwide, tens of thousands of satellites are being launched. In addition to messing up the images we obtain using our optical telescopes, they increase the potential interference problems for radio astronomy by orders of magnitude.
Although we will always need radio telescopes here on Earth—because they are cheaper, easier to operate, and can be used as scientific and technical education tools—there is more and more discussion about putting a radio telescope or two on the Moon.
Since the same side of the Moon always faces us here on Earth, we could place that radio telescope or two on the far side, where the Earth never rises above the horizon. This would block out all the interference from Earth and from all those tens of thousands of satellites. In addition, with few if any transmitters around, almost all the radio spectrum would be available for radio astronomy.
Of course, supporting the instruments would require a base with support and operating staff. Since the Earth never rises above the horizon on the far side of the Moon, relay satellites will be needed for communication with Earth. Finally, we have little knowledge of what is needed for the ongoing health of people in a permanently staffed lunar base. We will solve these issues, but don’t expect lunar radio observatories for a few years yet.
Saturn rises around midnight. Jupiter and Venus lie close together in the predawn sky. Venus is brighter and whiter. Mars is now lost in the sunset glow.
The Moon will be full on the 9th.