# How do aphelion and perihelion compare to one another?

Jan 23, 2016

Aphelion = 152 x ${10}^{6}$ km or 152 million km.
Perihelion = 147 x ${10}^{6}$ km or 147 million km.

#### Explanation:

Aphelion is the point in the orbit of a Planet when it is farthest away from it's Star.

Perihelion is the point in a Planet's orbit when it is closest to it's Star.

Lets take an example of the Earth.

The Average distance between the Earth and the Sun is about 149 million km.Average because the orbit of Earth around the Sun is not a perfect circle but an ellipse.

The Earth's Aphelion distance is about 152 million km with a Perihelion distance of about 146 million km.

You can calculate the Perihelion and Aphelion of any object if you know the eccentricity of the Object's orbit and the average distance between that object and the sun also known as the Semi-Major axis.

Aphelion and Perihelion distances can be easily calculated using the following formulas.

Aphelion = a( 1 + e)

Perihelion = a ( 1 - e)

Where,

a is the Average distance between the star and the Object aka Semi-major axis.

e is the eccentricity of the orbit.

In case of Earth, this can be calculaed as.

a = 1.50 x ${10}^{8}$ km
e = 0.0167

Aphelion = 1.50 x ${10}^{8}$ ( 1 + 0.0167 )

Aphelion = 152 x ${10}^{6}$ km or 152 million km.

Perihelion = 1.50 x ${10}^{8}$ ( 1 - 0.0167)

Perihelion = 147 x ${10}^{6}$ km or 147 million km.