Reference · The Sun, Moon and planets: pure parts
footprintAnglefunction
The angle at the Earth's centre between the point below a satellite and the edge of its footprint, in radians: the ground circle from which the satellite is above elevation.
It is acos(R cos(e) / (R + h)) - e for the Earth's radius R, the height h and the elevation e. A satellite on or under the ground, or an elevation of 90 degrees or more, has none.
Import it
import { footprintAngle } from "@johnmorrisdotca/chikyu-earth/space";Definition
function footprintAngle(heightKm: number, elevation?: number): numberParameters
| Name | Type | Description |
|---|---|---|
heightKm | number | The satellite's height above the ground, in kilometres. |
elevation (optional) | number | The least elevation, in degrees. 25 when left out. |
Returns
number
The angle, in radians, from 0 up to a quarter of a turn.
Examples
import { footprintAngle } from "@johnmorrisdotca/chikyu-earth/space";
console.log((footprintAngle(420) * 180) / Math.PI);6.760501126057435What it prints (run when this page was built)