Maharashtra State Board – Standard IX

Science

Chapter 18 – Observing Space: Telescopes

🔹 1. Fill in the blanks with the proper words.

1. The wavelength of visible light is between …….. and ………
Ans: The wavelength of visible light is between 400 nm and 800 nm.

2. GMRT is used for ……. waves.
Ans: GMRT is used for radio waves.

3. A certain X-ray telescope is named after scientist ………..
Ans: A certain X-ray telescope is named after scientist Subramanian Chandrashekhar.

4. The first scientist to use a telescope for space observation was ………………. .
Ans: The first scientist to use a telescope for space observation was Galileo Galilei.

5. The biggest optical telescope in India is situated at ……….
Ans: The biggest optical telescope in India is situated at the Aryabhatta Research Institute of Observational Sciences (ARIES), Nainital.

🔹 2. Form pairs

‘A’ Group‘B’ Group
(i) X-rays(d) Chandra
(ii) Optical Telescope(c) Hubble
(iii) Indian radio telescope(a) GMRT
(iv) Launching artificial satellites(b) ISRO

Ans: The correct pairs are as shown in the table above.

🔹 3. What are the difficulties in using ground based optical telescopes? How are they overcome?

Ans: Difficulties:

  1. The visible light coming from heavenly bodies has to pass through the Earth’s atmosphere before reaching the surface.
  2. During this journey, some of the light is absorbed by the atmosphere, reducing its intensity.
  3. Changes in atmospheric pressure and temperature cause turbulence in the atmosphere.
  4. This turbulence changes the path of light rays slightly and makes the image appear shaky.
  5. Optical telescopes cannot be used during the day because of bright sunlight.
  6. At night, city lights and cloudy weather also create difficulties in observation.

Solutions:

  1. To reduce these problems, optical telescopes are located on mountains in uninhabited places where the air is thin and clear.
  2. To completely avoid atmospheric disturbances, telescopes are placed in space above the Earth’s atmosphere.

🔹 4. Which type of telescopes can be made using a concave mirror, convex mirror, plane mirror and a lens? Draw diagrams of these telescopes.

Ans:

  1. A Newtonian telescope can be made using a concave mirror, a plane mirror, and a lens (eyepiece).
  1. A Cassegrain telescope can be made using a concave mirror, a convex mirror, and a lens.
  1. A Refracting telescope is made using two or more lenses.

🔹 5. Study the figure and answer the following questions:

a. What type of telescope is shown in the figure?

Ans: The telescope shown in the figure is a Newtonian telescope (reflecting telescope).

b. Label the main parts of the telescope.

Ans: The main parts of the telescope are:

  1. Concave mirror
  2. Plane mirror
  3. Eyepiece
  4. Tube of the telescope
  5. Incoming light rays

c. Which type of mirror does the telescope use?

Ans: The telescope mainly uses a concave mirror.

d. What other type of telescope uses a curved mirror?

Ans: The Cassegrain telescope also uses a curved mirror.

e. Explain the working of the above telescope.

Ans:

  1. Light rays coming from a distant object fall on the concave mirror.
  2. The concave mirror reflects the light rays towards its focus.
  3. Before the rays meet at the focus, a small plane mirror deflects them sideways.
  4. The light rays then pass through the eyepiece.
  5. A magnified image of the object is formed, which we can observe.

🔹 6. Answer the following questions.

a. Explain the construction of Galileo’s telescope.

Ans:

  1. Galileo’s telescope is made using two lenses.
  2. The lens facing the object is called the objective lens, and it is large to collect maximum light.
  3. The lens near the eye is called the eyepiece.
  4. The objective lens forms an image, and the eyepiece magnifies it.
  5. This type of telescope is called a refracting telescope.

b. Explain the construction of a radio telescope.

Ans:

  1. A radio telescope consists of one or more large parabolic dishes.
  2. The radio waves coming from space are reflected by the dish.
  3. These waves converge at the focus of the dish.
  4. A radio receiver placed at the focus collects the signals.
  5. The collected information is sent to a computer, which processes it and forms an image of the source.

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

Ans:

  1. Light from heavenly bodies gets absorbed and scattered by the atmosphere.
  2. Atmospheric turbulence causes images to appear unsteady.
  3. Sunlight during the day prevents observation.
  4. At night, city lights and pollution affect visibility.
  5. Therefore, optical telescopes are placed on high mountains in uninhabited areas where the air is clear and pollution is minimal.

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

Ans:

  1. X-rays are emitted by distant heavenly bodies.
  2. The Earth’s atmosphere absorbs X-rays before they reach the surface.
  3. Therefore, X-ray telescopes must be placed in space above the Earth’s atmosphere to detect these rays.
Scroll to Top