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

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

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🥁 The reflecting telescope:
A)The Newtonian telescope:
The reflecting telescopes are
mainly of two types: Newtonian and Cassegrain.
It is a type of reflecting telescope that uses a concave primary mirror and a flat diagonal secondary mirror. Light rays coming from space are reflected by the concave mirror.

Before these reflected rays converge at the focus, they are deflected again by a small plane mirror. 
As a result, they get focused at a point lying on the perpendicular to the axis of the telescope’s cylinder. They pass through the eyepiece and we get a magnified image of the source.
(⭐converge: come together, meet, join, combine, gather)

🎊 The Cassegrain telescope:
 The construction of a Cassegrain type of telescope is shown below 👇

It is a combination of a primary concave mirror and a secondary convex mirror. 

The Cassegrain telescope also uses a concave mirror. However, here light rays, after reflection from the concave mirror are reflected towards it by a small convex mirror.
They pass through a hole in the center of the concave mirror and then through the eyepiece situated at the back of the mirror. 
The eyepiece gives us a
magnified image of the source.
Use: For Observing the Moon, planets, double stars, and narrow-field views of deep-sky objects.

🎻
The largest optical telescope in Asia:
In India, we have several telescopes with concave mirrors of 2 m diameter that have been in use for many years.
 The biggest optical telescope in India, having a mirror of 3.6 m diameter is situated in the
Aryabhatt Research Institute of
Experimental Sciences, Nainital. This is the largest optical telescope in Asia.

📡 Radio telescope:

• 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.

🚀 Hubble Telescope: 

•  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.

🔭 X-ray telescope Chandra:

•  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

💡 Astrosat
In 2015, the Indian Space Research Organization
(ISRO) launched an artificial satellite called Astrosat, in space. This satellite has ultraviolet (UV) and X-ray telescopes and detectors. 
Most of the parts used in this satellite are made in India. 
It is a 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.

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