Explain how size of a planet or star is measured.

1.	Explain how size of a planet or star is measured.
Answer» 1. To determine the diameter (d) of a planet or star, two diametrically opposite points of the planet are viewed from the same observatory. 2. If d is diameter of planet or star, angle subtended by it at any single point on the Earth is called angular diameter of planet. 3. Let angle α be angle between these two directions. 4. If distance between the Earth and planet or star (D) is known, α = \(\frac{d}{D}\) 5. This relation gives, d = α D Thus, diameter (d) of planet or star can be determined.

Answer»

1. To determine the diameter (d) of a planet or star, two diametrically opposite points of the planet are viewed from the same observatory.

2. If d is diameter of planet or star, angle subtended by it at any single point on the Earth is called angular diameter of planet.

3. Let angle α be angle between these two directions.

4. If distance between the Earth and planet or star (D) is known, α = \(\frac{d}{D}\)

5. This relation gives, d = α D

Thus, diameter (d) of planet or star can be determined.

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