Comments (2)
Hi,
To determine retrograde you have to calculate second position in future. For example + 1 hour or a day.
Then compare with current position.
from ephemeris.
Hey @cptolemy ! For what its worth, my fork of this repo just implemented retrograde planet and shadow phase calculations into version 1.2.0 https://github.com/0xStarcat/Moshier-Ephemeris-JS/tree/master
Not sure if I'll be able to get it merged here, but feel free to have a look at how I did it in the files motion.js
and HeliocentricOrbitalBody.js
To answer your question, yes you need 2 observations - my fork compares the apparentLongitude
of the body now, and the body 1 second from now, and if the difference is <= 0, I designate it retrograde in the results.
from ephemeris.
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from ephemeris.