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This is an old revision of DefiningTheClassicalOrbitalElements made by jfl on 2012-01-13 12:24:46.

Defining the classical orbital elements

Semi-major axis

The size of the orbit is described by the semi-major axis = a, which is one-half the distance across the major (long) axis of the orbit.

Eccentricity

Eccentricity = e specifies the shape of an orbit and is given by the ratio of the distance between the two foci and the length of the major axis.

e = 2c/2a

The eccentricity of a circular orbit is zero, and can range from zero to less than one for an ellipse.

Inclination (i) [degrees]

The angle between the plane of the equator and the orbit plane.

Right Ascension of the Ascending Node (Ω)

The angle between the sun and the intersection of the equatorial plane and the orbit on the first day of spring on the north hemisphere. The day is called vernal equinox. Looking down from above the north pool, the right ascension of ascending node is positive counter-clockwise.

Argument of Perigee (w) [degrees]
The angle between the ascending node and the orbit's point of closest approach to the earth (perigee).

True Anomaly (v)[degree]
The angle between perigee and the vehicle in the orbit plane.