Science Answer the following question.

A Cassegrain telescope can be made using a convex mirror, concave mirror and a lens.

A refracting telescope can be made using two or more lenses.

• The intensity of visible light coming from a heavenly body decreases due to absorption as it passes through the Earth’s atmosphere.
• Due to changes in atmospheric temperature and pressure light rays change their path.
• Because of sunlight, we cannot use optical telescopes during the day.
• During the night, city lights and cloudy weather cause difficulties.

Solution:

• To reduce these problems, optical telescopes are situated on top of mountains, in uninhabited places.
• To get rid of all the above problems completely, the telescope is placed above the earth’s atmosphere, in space.

• This satellite was launched by Indian Space Research Organization (ISRO).
• It has ultraviolet and X-ray telescopes and detectors. Most of the parts used in this satellite are made in India.
• It is an unique system having different kinds of telescopes on a single satellite. Indian scientists are studying various aspects of the Universe using the data obtained with these telescopes.

• The INSAT and GSAT series of satellites support our telecommunication network, television broadcasting and meteorological services.
• It is because of them that telephone, television and internet services are available everywhere in the country.
• The EDUSAT satellite is used exclusively for education.
• The IRS satellite series is used for the monitoring and management of natural resources as well as disaster management.
• Astrosat: It has ultraviolet and X-ray telescopes and detectors. It is a unique system having different kinds of telescopes on a single satellite.

• Giant Meterwave Radio Telescope (GMRT) is a large radio telescope erected at Narayangaon near Pune.
• It uses radio waves having wavelengths of about a metre, coming from heavenly bodies to study those bodies. This telescope is actually 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. It works as a single dish having a diameter of 25 km.
• GMRT gives the same data that we would have got from a telescope having a single dish of 25 km diameter.
• Scientists study the solar system, solar winds, pulsars, supernova, interstellar hydrogen clouds, etc. with the help of the GMRT.

• In 1990, the National Aeronautics and Space Administration launched into space an optical telescope called the Hubble telescope.
• It has a mirror of diameter 94 inches and is orbiting the earth at a height of 589 km from it.
• This telescope is still working and has helped to make important discoveries.

Chandra Telescope:

• 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.