On the earth, optical telescopes (which collect visible light at longer wavelengths) and radio telescopes (which collect radio waves with the shortest wavelengths) have to peer through layers of the planet’s atmosphere.
While it is becoming increasingly difficult for optical instruments to see through the polluted skies, radio telescopes also contend with radio and TV signals adding to the cacophony of the electromagnetic ‘hiss’ from the communications channels used by radar systems, aircraft, and satellites.
It also does not help that the earth’s ionosphere blocks radio waves coming from outer space.
Scientists tried to find a way out of this by launching radio telescopes into orbit around the earth.
But this only made the problem worse, as orbiting telescopes started receiving radio noise from the whole planet along with signals from outer space
As a remedy astronomers are looking forward to opening a new window on the universe by posting high-resolution telescopes on the moon and in orbit around it.
The pristine, airless desolation of the moon provides optical telescopes crystal-clear seeing conditions throughout the long lunar night, which lasts two weeks at a time.
Radio telescopes on the lunar far side will also be protected by a 3,475-km-thick wall —a.k.a. the moon (its diameter is 3,476 km) — that blots out radio transmissions from the earth and electrically charged plasma winds blowing from the Sun.
The universe went ‘quiet’ for tens of millions of years afterwards as gravity began to build the first stars and galaxies.
This period of time between the initial scattering of the cosmic microwave background (CMB) radiation and the birth of the first stars is known as the Dark Ages.
It is believed the neutral hydrogen pervading the cosmos during the Dark Ages absorbed some of the CMB radiation to produce an extremely small dip in the frequency of the spreading radio waves.
Terrestrial instruments can’t detect this minute frequency drop.
Instead, moon-based instruments are our best bet to spot this signal from the Dark Ages, which would be essentially free from the influence of any starlight (since there were no stars then).
LuSEE Night
Lunar Surface Electromagnetic Experiment, or LuSEE Night, a joint NASA-Berkeley Lab project, scheduled for launch in December 2025 to study the Dark Ages period because it connects how the early universe evolved into the universe we see today
It is going to land on the far side of the moon, near the equator of the moon, and almost exactly opposite from the earth. This location is helpful because it best shields radio frequency noise coming from the earth
PRATUSH radio telescope
Indian scientists are planning to do with the radio telescope PRATUSH (Probing ReionizATion of the Universe using Signal from Hydrogen), to study the universe from the moon’s far side.
PRATUSH is being built by the Raman Research Institute (RRI) in Bengaluru with active collaboration from the Indian Space Research Organisation (ISRO).
Initially, ISRO will place PRATUSH into orbit around the earth. After some fine-tuning, the space agency will launch it moonwards.
Other Radio telescope Projects
China, with a moon-orbiting radio telescope scheduled for launch in 2026.
ESA is getting ready to launch a radio telescope to the moon’s far side on board its lunar lander, ‘Argonaut’, by 2030
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