Question

Answer the following questions.

a. Explain the construction of Galileo’s telescope.

b. Explain the construction of a radio telescope.

c. Why are optical telescopes located in uninhabited places on mountains?

d. Why can an X-ray telescope not be based on the earth?

Answer 1

a. In 1906, Galileo constructed a telescope which provides an erect image of an object only with the help of two lenses. The Galileo's telescope consists of two lenses located at the ends of a long tube as shown in the figure below. The objective was a convex lens and eye piece was a concave lens.


b. These telescopes are used to see radio waves coming from space. It has one or more dishes of parabolic shape. The rays coming from the distant source are first reflected by these dishes which converges at the focus. A radio receiver is placed at the focal point, which gathers the information. The gathered information is then passed on to a computer which analyses it and construct an image of the source.


c. Optical telescopes situated on the surface of Earth, does not produce images of good quality of the following reasons:

• 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.

Thus, optical telescopes are located in uninhabited places and on higher altitudes such as on top of mountains to reduce the above problems in appreciable amount.

d. X-ray telescope cannot be based on the Earth because X-rays do not reach the Earth surface as they are blocked by the Earth's atmosphere.