Question

What are the difficulties in using ground based optical telescopes? How are they overcome? [ 3 Marks]

Answer 1

The difficulties faced in using ground based telescopes due to which it does not make good quality observations are:

• Intensity of light rays reaching the Earth's surface decreases as some of the light is absorbed by the atmosphere.
• The change in atmospheric pressure and temperature cause the light rays to change their path slightly and thus shake the position of the image.
• We cannot use optical telescopes during day time because of the presence of sunlight.
• Even in night, city lights and cloudy weather can cause hindrance in observing the heavenly bodies.

[ 1.5 Marks]

To overcome the above problems, telescopes are now being erected in space itself. Some of the telescopes in space are:

• Hubble telescope: It is an optical telescope launched by the National Aeronautics and Space Administration in 1990. It is orbiting the Earth at a height of 589 km from it and has a mirror of diameter 94 inches.
• Chandra: It is an X-ray telescope launched by the National Aeronautics and Space Administration in 1999. Special mirrors which can reflect X-rays are used in this telescope. [ 1.5 Marks]