Question
Explain how size of a planet or star is measured.
✓
Answer
- To determine the diameter (d) of a planet or star, two diametrically opposite points of the planet are viewed from the same observatory.
- 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.
- Let angle α be angle between these two directions.
- If distance between the Earth and planet or star (D) is known, $\alpha=\frac{ d }{ D }$
- This relation gives, d = α D
Thus, diameter (d) of planet or star can be determined.
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