Question

Define Parallax. Discuss angular method to determine the diameter of a

planet.​

Answer 1

Answer:

The parallax angle is the angle between the Earth at one time of year, and the Earth six months later, as measured from a nearby star. Astronomers use this angle to find the distance from the Earth to that star. ... Because of this, nearby stars will seem to move relative to distant, "background" stars.

Explanation:

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Answer 2

Parallax is the effect due to which the position or direction of an object appears to be different when viewed from other positions. It is the apparent distance of the object due to the change in positions of the observer.

Angular method to determine the diameter of a planet:

Let the distance of Earth = D

D = bα

where b is the distance between observatories on earth

α = angle between two directions along which the planet was viewed from different directions.

Let d = diameter of the particular planet

and β = angle subtended by the diameter d at  a point A on earth.

Since D is very large:

d/D <<< 1

Let AB be an arc of length d with centre at A.

Then distance = AB = d = Dα

α = d/D

→ d = αD

Therefore, the diameter of the planet will be αD.