I have the argument of perihelion, semi-major axis, eccentricity, inclination and mass. I have tried to look this up but get conflicting answers. Any help would be appreciated.

(Edit) One physics forum gave me this formula,

$$r = a \frac{1 - e^2}{1 + e \cos \theta}$$

Reference: https://www.physicsforums.com/threads/position-of-ascending-and-descending-nodes.534665/ where to my understanding, theta is the true anomaly, this forum also states to minus the argument of perihelion from 360 to get my true anomaly value.

Another stated to do $2 \pi$ - arg of perihelion, though I think this Doesnt apply as it is a Keplerian orbit.

  • $\begingroup$ Please edit your question to show information on the conflicting answers and how far you have gotten. $\endgroup$ Mar 31 at 21:37
  • 4
    $\begingroup$ All the information you have provided is completely independent of longitude of the ascending node, or of the true anomaly. If all you have is the argument of perihelion, semi-major-axis, eccentricity, inclination, and mass of the central body, any value of Longitude of the ascending node or of the True Anomaly could be valid values. $\endgroup$
    – notovny
    Mar 31 at 22:39
  • 2
    $\begingroup$ The semi-major axis, AOP, eccentricity, inclination, ascending node, and true anomaly are all needed for you to determine a body’s position in orbit. As @notovny said, you can’t just find the value of one (or in your case two) parameter using the rest. Are you asking for the value of the parameters after some time passes? But in that case you require the initial values as well. $\endgroup$
    – Shawn Lim
    Apr 1 at 1:49
  • 1
    $\begingroup$ Look at the diagram. en.wikipedia.org/wiki/Argument_of_periapsis True anomaly is measured from the perihelion. And arg of perihelion is the angular distance (in the orbit plane) from the ascending node to the perihelion. So you need the longitude of the ascending node to determine how the orbit plane is rotated relative to the X axis of the reference plane. $\endgroup$
    – PM 2Ring
    Apr 1 at 19:24
  • 3
    $\begingroup$ On your edit--360 - arg of perihelion and 2pi - arg of perihelion mean the same thing. The first is in degrees, the second is in radians. Both apply equally. $\endgroup$
    – Erin Anne
    Apr 1 at 19:26


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