Question

the position of a planet when it is nearest to the sun is called

Answer 1

Sun is not at the center of an elliptical orbit, all the planets while orbiting the sun, move closer and further away from it.

The particular place where a planet is closest to the Sun is called Perihelion and when the planet is farthest from the Sun then it is at Aphelion.

The words "aphelion" and "perihelion" derive from the Greek.

"Helios" means ‘Sun’ and "peri" means ‘near’, and "apo" means ‘away from’.

Answer 2

Perihelion
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The position of a planet when it is nearest to the sun is called Perihelion 
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1) The position of a planet when it is Farthest to the sun is called Apherilon 

2) Sun is the centre of solar system 

3) there are 8 planets in solar system