GS Paper III

News Excerpt:

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.

 More about the news:

• There are numerous proposals to do this from astronomers around the world — including one from India called PRATUSH.

Shortcomings of Earth-based telescopes:

• 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.

Concept of Lunar orbit telescope:

• 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. 
• So astronomers are now considering placing optical and radio telescopes on the far side of the moon, which always faces away from the earth.
• The pristine, airless desolation of the moon provides optical telescopes crystal-clear seeing conditions throughout the two-week-long lunar night.
• Radio telescopes on the lunar far side will also be protected by the moon (it will blot out radio transmissions from the earth and electrically charged plasma winds blowing from the Sun).

Why renewed interest in Moon based telescopes?

• In the past, the enormous costs involved discouraged scientists from setting up lunar telescopes. 
• But renewed interest among spacefaring nations to return to the moon promises to open up “the most radio-quiet location in the solar system.

PRATUSH : Probing ReionizATion of the Universe using Signal from Hydrogen

• PRATUSH is a future radiometer in lunar orbit that will reveal the Cosmic Dawn of our Universe. 
• It is being built by the Raman Research Institute (RRI) in Bengaluru with active collaboration from the Indian Space Research Organisation (ISRO).
• ISRO will place PRATUSH into orbit around the earth. After some fine-tuning, the space agency will launch it moonwards. 
• Although earth orbit will have significant radio frequency interference (RFI), it will have advantages compared to ground-based experiments, such as operating in free space and lesser ionosphere impact.
• PRATUSH in lunar orbit will have the ideal observing conditions operating in free space with minimal RFI and no ionosphere to speak of. 
• It will carry a wideband frequency-independent antenna, a self-calibrating analog receiver and a digital correlator to catch radio noise in the all-important signal from the Dark Ages.

Significance of PRATUSH:

• PRATUSH will answer the question of when the first stars formed in our universe, the nature of the first stars, and what was the light from the first stars or, in other words, the colour of the light of Cosmic Dawn. 
• PRATUSH will be the pioneering space telescope that will reveal, for the first time, the history of our infant Universe as it transformed after the Big Bang - from cold gas into stars and galaxies and the universe as we know it today. PRATUSH, as its name denotes, will inform us of the first rays of the first suns in the infant universe.

Moon based telescopes programmes of other countries/Space agencies:

• USA:

• • Lunar Surface Electromagnetic Experiment, or LuSEE Night is a joint NASA-Berkeley Lab project, scheduled for launch in December 2025.
    • 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.
  • NASA’s Long-Baseline Optical Imaging Interferometer is scheduled to be launched in parts before 2030.
    • Once assembled on the moon’s far side, it will study magnetic activity on stars and the centres of active galaxies in visible and ultraviolet wavelengths.

• The European Space Agency (ESA):

• • The European Space Agency (ESA) will launch a radio telescope to the moon’s far side on board its lunar lander, ‘Argonaut’, by 2030. 
  • Other European projects include super-sensitive detectors to hunt for the elusive ripples of gravitational waves in space-time and an infrared telescope located inside a permanently shadowed crater near the lunar south pole.

• China:

• China has a moon-orbiting radio telescope scheduled for launch in 2026. 
• Another of its satellites, Queqiao-2 which is intended as a communications relay between the earth and future missions, probably entered into orbit around the moon on March 24 2024. 

Conclusion:

As astronomers open new windows from the moon to look at the far reaches of the universe, who knows what discoveries await them. One thing is certain: they are in for some exciting times as the cosmos yields clues to some of its greatest mysteries, such as dark energy (which pushes the universe in every direction at an accelerating rate), primordial black holes and, indeed, the very nature of the cosmos.