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orbital element

(parameters describing an orbit)

Orbital elements are parameters that describe an orbit (the path of an astronomical object gravitationally bound to another, particularly, a repeating pattern) according to a reference plane and a direction through that plane. Commonly used are six elements to describe a Keplerian orbit. Two of them describe shape and size of the orbit:

The other four elements describe the orbit's attitude and the current phase, the latter which can be thought of as the current position of the orbiting body within its orbital path. These four are more challenging to describe so I'll use the following orbit-related terms:

The remaining four orbital elements:

These six orbital elements are sufficient to describe the particulars of the orbit at a given moment, given a reference time (epoch), the orbit's position, a given reference plane, and a direction across the plane considered to be "upward". These givens could be provided by a given coordinate axes within a given frame of reference, a position vector to identify the orbit's position (e.g., to one of its foci), and a unit vector to identify a reference plane and the "upward" direction crossing it.


(orbits,celestial mechanics,kinematics)
Further reading:
https://en.wikipedia.org/wiki/Orbital_elements
https://astronomy.swin.edu.au/cosmos/o/Orbital+Elements
https://farside.ph.utexas.edu/teaching/celestial/Celestial/node34.html
https://oer.pressbooks.pub/lynnanegeorge/chapter/chapter-3-the-classical-orbital-elements-coes/
https://www.planetary.org/articles/3380

Referenced by pages:
apsis
circumstellar disk
semi-major axis (a)
solar eclipse
two-line element set (TLE)

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