9th Science II, 18th Chap. Observing space: Telescopes 🔭 2.

• Many heavenly objects emit radio waves in addition to visible radiation. We cannot see this radiation with our eyes. Hence, a special type of telescope is used to receive these rays. It is called a radio telescope. 
•  A Radio telescope is made from one or more dishes of a particular parabolic shape. As in an optical telescope, the incident radio waves are reflected by these dishes and converge at the focus. A radio receiver is placed at the focal point. 
• The information gathered by this receiver is passed on to a computer which analyses it and constructs an image of the source.
• Feature: Unlike optical telescopes, radio telescopes can be used in the daytime as well as at night.

📡 Giant Meter Wave Radio Telescope (GMRT):

• A large radio telescope called the Giant Meter Wave Radio Telescope (GMRT) has been erected at Narayangaon near Pune. 
• It uses radio waves having wavelengths of about a meter, used to study astrophysical phenomena at low radio frequencies (40 to 1450 MHz) coming from planets and stars to study those heavenly bodies. 
• This telescope is a collection of 30 dishes, each having a diameter of 45 m.
• It is called a giant telescope as the arrangement of the 30 dishes over an area which measures up to 25 km across, is made in such a way that it works as a single dish having a diameter of 25 km. This means that the GMRT gives the same data that we would have got from a telescope having a single dish of 25 km diameter! 
• GMRT has been made by Indian scientists and engineers at a minimum cost.
•  It is a world-standard research facility.
• Use:  Scientists study the solar system, solar winds, pulsars, supernovas, interstellar hydrogen clouds, etc. with the help of the GMRT. 
• Scientists from all over the world come to India to make use of this facility.

•  In 1990, the National Aeronautics and Space Administration launched into space an optical telescope called the Hubble Telescope. 
• Hubble has changed humanity’s understanding of the universe.
• The Hubble Telescope has a mirror diameter of 94 inches and is orbiting the Earth at a height of 589 km. 
• This telescope is still working and has helped to make important discoveries.
• Discoveries: The Hubble Space Telescope has made many discoveries, including Black holes, Exoplanet atmospheres, Supernova 1987a, Distant galaxies, etc.

•  In 1999, the National Aeronautics and Space Administration launched an X-ray telescope named Chandra, in space, to study X-rays coming from heavenly objects. 
• Special mirrors which can reflect X-rays were used in this telescope.
• Chandra has given us very useful information about stars and galaxies.
• The telescope is named after the famous Indian scientist Subramanian Chandrashekhar.
• Chandra orbits above Earth’s atmosphere at an altitude of up to 139,000 km (86,500 mi). 

☄️ Indian Space Research Organization (ISRO) Bengaluru:

1. ISRO Institute was established in 1969 to develop technology for making and launching artificial satellites. 
2. To date, ISRO has successfully launched a large number of satellites. 
3. ISRO’s program is foremost among the successful programs undertaken by independent India. 
4. India’s progress in space science has played a big role in national and social development.
5. The INSAT and GSAT series of satellites support our telecommunication network, television broadcasting, and meteorological services. 
6. It is because of them that telephone, television, and internet services are available everywhere in the country. 
7. The EDUSAT satellite in this series is used exclusively for education. 
8. The IRS satellite series is used for the monitoring and management of natural resources as well as disaster management.
9. Website: www.isro.gov.in