# How do you calculate the perihelion distance of an object in orbit?

##### 1 Answer
Feb 22, 2016

The orbit size is wholly known when the semi-major axis a and eccentricity e are known. The perihelion is a ( 1 $-$ e).

#### Explanation:

For the Earth, a = 14959262 km and e is 0.01671. Perihelion =147.1 million km, nearly.