astro.Function.equatorialVelocity

@elite-dangerous-almanac/core / astro / equatorialVelocity

Function: equatorialVelocity()

equatorialVelocity(body): number | null

Defined in: src/astro/body-orbit.ts:222

How fast a body's equator moves as it turns, in metres per second.

Parameters

body

BodyProperties

The body. Needs Radius and RotationPeriod.

Returns

number | null

The equatorial speed in m/s, or null when either is missing. A body the scan reports as not rotating carries no period, and answers null rather than 0.

Remarks

2πR / T. This is the ground speed a point on the equator carries, which is why a fast rotator is worth knowing about before landing on one: the surface of a neutron star spinning in milliseconds is moving at a sizeable fraction of light speed.

Speed is a magnitude, so a retrograde body — written with a negative RotationPeriod — reads the same as a prograde one turning as fast.

Throws

If body is not an object.

Example

import { equatorialVelocity } from '@elite-dangerous-almanac/core/astro/body-orbit';

// Earth: about 465 m/s at the equator.
equatorialVelocity({ Radius: 6_378_137, RotationPeriod: 86164.1 }); // -> 465.1…

// Retrograde is the same speed, the other way round.
equatorialVelocity({ Radius: 6_378_137, RotationPeriod: -86164.1 }); // -> 465.1…