International Space Agencies – Missions and Discoveries

GRAPES-3 Experiment


Mains Paper 3: Science & Technology | Awareness in the fields of IT, Space, Computers, robotics, nano-technology, bio-technology

From UPSC perspective, the following things are important:

Prelims level: GRAPES-3 Experiment

Mains level: Particulars and importance of the Experiment


  • For the first time in the world, researchers at the GRAPES-3 muon telescope facility in Ooty have measured the electrical potential, size and height of a thundercloud that passed overhead on December 1, 2014.

GRAPES-3 Experiment

  • GRAPES-3 (Gamma Ray Astronomy PeV EnergieS phase-3) is designed to study cosmic rays with an array of air shower detectors and a large area muon detector.
  • It aims to probe acceleration of cosmic rays in the following four astrophysical settings.
  • It is located at Ooty in India and started as a collaboration of the Tata Institute of Fundamental Research, Mumbai, India and the Osaka City University, Osaka, Japan.

Measuring the potential of a Thunderstorm

  • Using a computer simulation and the observed Muon intensity variations, the group worked out the relationship with the electric potential of the cloud.
  • They calculated that the potential of the cloud they were studying was approximately 1.3 Giga Volts.
  • At 1.3 GV this cloud had 10 times higher potential than the previous record in a cloud.
  • No one has ever measured potential, size and height of a thundercloud simultaneously.

Utility of this study

  • Learning about the properties of thunderclouds can be useful in navigation of aircraft and preventing short circuits.

Cloud structure are better assessed

  • Clouds have negative charges along their lower side and positive charges on top and can be several kilometres thick.
  • If balloons are used to measure the potential difference between the top and bottom, they will take hours to traverse the distance.
  • Unfortunately, thunderstorms last only for about 15-20 minutes, and this method fails.


What are Muons? How are they detected?

  • Muons and other particles are produced when cosmic rays bombard air particles surrounding the earth.
  • The muons produced can have positive or negative charge.
  • When a positively charged muon falls through a cloud, it loses energy.
  • If its energy falls below 1 giga electron volt (GeV), which is the threshold of detection of the GRAPES-3 muon telescope, it goes undetected.
  • On the contrary, a negatively charged muon gains energy when falling through the cloud and gets detected.
  • Since there are more positive than negative muons produced in nature, the two effects don’t cancel out, and a net change in intensity is detected.
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