Planets

Low-precision heliocentric positions of Mercury through Pluto and the Earth-Moon barycenter, from the Keplerian-element approximations of Standish & Williams (JPL Solar System Dynamics). The Sun and the Moon are not valid bodies.

For higher accuracy, use the jplephem module which provides full JPL ephemeris data.

planets

Low-precision planetary ephemerides from the Keplerian-element approximations of E. M. Standish and J. G. Williams, "Keplerian Elements for Approximate Positions of the Major Planets", JPL Solar System Dynamics: https://ssd.jpl.nasa.gov/planets/approx_pos.html

heliocentric_pos(planet, time)

Return the position of the given body in the Heliocentric coordinate system (origin is the Sun)

Axes are ICRF (J2000 equatorial).

Note: Valid bodies are Mercury through Pluto and the Earth-Moon barycenter (satkit.solarsystem.EMB); the Sun and the Moon raise RuntimeError

Note: Valid from 3000 BC to 3000 AD, with a more accurate element set for 1800 AD to 2050 AD

Note: This is less accurate than using the jpl ephemeris, but involves fewer calculations. JPL's approximate errors in heliocentric ecliptic longitude / latitude / range run from 15" / 1" / 1000 km (Mercury, 1800-2050) to 2000" / 30" / 8 million km (Uranus, 3000 BC-3000 AD); see https://ssd.jpl.nasa.gov/planets/approx_pos.html. The Uranus, Neptune and Pluto elements follow the orbit about the solar-system barycenter, so from 1800 to 2050 their heliocentric errors are dominated by the Sun's unmodeled barycentric motion (up to ~2 arcmin and ~2.3 million km).

Parameters:

Name	Type	Description	Default
planet	solarsystem	Mercury through Pluto, or EMB	required
time	time | ndarray | list	Time[s] at which to return position	required

Returns:

Type	Description
NDArray[float64]	numpy.ndarray: 3-vector of Cartesian position in meters, with the origin at the Sun. If input is list or numpy array of N times, then r will be Nx3 array

Example

import numpy as np
t = satkit.time(2024, 1, 1)
pos = satkit.planets.heliocentric_pos(satkit.solarsystem.Mars, t)
print(f"Mars distance from Sun: {np.linalg.norm(pos)/satkit.consts.au:.2f} AU")