Could someone please explain to me how I can extract velocity component values from Stellarium, for a given planet?

Question

For a project that I am currently working on, I would like to know how one could extract velocity component values ($v_x$, $v_y$ and $v_z$) for a planet from the Stellarium software. The current information panel for a planet does show its orbital velocity (which is the resultant velocity, $v$) but does not give the individual $v_x$, $v_y$ and $v_z$ values that result in that velocity.

What I essentially need, is to establish a velocity heading for the planet.

Any help (code-based/mathematical) would be much appreciated! Thanks in advance!

Answer 1

To follow up on the helpful comments below your question, here's a program that will do what you need, but without using Stellarium.

If you really need to use Stellarium then hopefully someone will find a way to help you.

This uses the Python package Skyfield and you can see a lot of documentation on that site and elsewhere. Right now I've specified the DE421 ephemeris, but there are many to choose from. This one only works +/- 100 or 200 years I think, others go for thousands of years in the past or future.

If you would like to use NASA JPL's Horizons web interface online, here are some instructions. It uses some of the same Development Ephemerides that Skyfield downloads for you.

Here's some output for roughly 2019-10-02 07:18:59 UTC which is the moment when you posted your question.

                    relative to solar system barycenter
               x            y           z            vx        vy          vz
Sun        -453731.5    1039601.2    451057.1     -0.015      -0.002       0.0
Earth     1.4764e+08   2.1455e+07   9.3005e+06    -4.9362     26.9295     11.6751
Jupiter  -2.2857e+07  -7.2214e+08  -3.0898e+08    12.9012      0.3382     -0.1690
Mumbai    1.4763e+08   2.1454e+07   9.3025e+06    -4.8369     26.5009     11.6749

                      relative to Earth's geocenter

Sun      -1.4809e+08  -2.0416e+07  -8.8494e+06     4.9215    -26.9312    -11.6754
Earth     0.           0.           0.             0.          0.          0.
Jupiter  -1.7050e+08  -7.4360e+08  -3.1828e+08    17.8374    -26.5912    -11.844
Mumbai   -5873.8303   -1362.2932     2072.3226  9.9338e-02    -4.2861e-01 -1.9206e-04

                           relative to Mumbai

Sun      -1.4809e+08  -2.0414e+07  -8.8515e+06     4.8222    -26.5026    -11.6752
Earth       5873.83     1362.29     -2072.32      -9.9338e-02  4.2861e-01  1.9206e-04
Jupiter  -1.7049e+08  -7.4359e+08  -3.1828e+08    17.7381    -26.1626    -11.8439
Mumbai    0.           0.           0.             0.          0.          0.

Here's a Python 3 script for that output as an example

import numpy as np
import matplotlib.pyplot as plt
from skyfield.api import Topos, Loader, EarthSatellite

load    = Loader('~/Documents/fishing/SkyData')  # avoids multiple copies of large files
data    = load('de421.bsp')
ts      = load.timescale()

sun     = data['sun']
earth   = data['earth']
jupiter = data['jupiter barycenter']
mumbai  = earth + Topos(latitude_degrees  = 18.98,
                        longitude_degrees = 72.83,
                        elevation_m       =  20.0)
time    = ts.utc(2019, 10, 2, 7, 18, 59)

things     = (sun, earth, jupiter, mumbai)
names      = ('Sun', 'Earth', 'Jupiter', 'Mumbai')
positions  = [thing.at(time).position.km for thing in things]
velocities = [thing.at(time).velocity.km_per_s for thing in things]

for name, position, velocity in zip(names, positions, velocities):
    print(name, position, velocity)

print("relative to Earth's Geocenter")
for name, position, velocity in zip(names, positions, velocities):
    print(name, position-positions[1], velocity-velocities[1])

print("relative to Mumbai")
for name, position, velocity in zip(names, positions, velocities):
    print(name, position-positions[3], velocity-velocities[3])