# How is velocity calculated at perihelion?

Mar 10, 2016

4-significant digits (sd) approximation: 30.79 km/s

#### Explanation:

Easy formula for velocity at perihelion and aphelion:

If V is the speed at the distance equal to semi-major axis a ( at an end of the minor axis) of the orbit, Vp and Va are speeds at perihelion and aphelion and e is the orbit eccentricity.
$V p = V \left(\frac{1 + e}{1 - e}\right) \mathmr{and} V a = V \left(\frac{1 - e}{1 + e}\right)$
V - 29.774 km/s, nearly. e = 0.01671, nearly.

The directions of motion at perihelion and aphelion are perpendicular to the radius from the Sun to the Earth.