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How to Determine if a Planet is Moving Retrograde

-- Manpreet | March 25, 2021

Question:

How can we find mathematically that a planet in our solar system is moving retrograde as seen from earth on a given moment
we have following values
Longitude of Sun and subject planet
x y z coordinates of earth and planet
and other basic and other values like RA and declination etc.

-- Manpreet

Answer:

I believe that this question has been answered on the Physics StackExchange forum. Observationally, if you can measure the right ascension of the planet over time you will notice that the right ascension of a planet in retrograde motion will decrease.

-- Jeff Mangum

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