## Explanation Of Orbital Elements

Epoch

The epoch of osculation of the orbital elements.

M

Mean anomaly at the epoch.

n

Mean daily motion (in degrees/day).

a

Semimajor axis (in AU).

z

Reciprocal semimajor axis (in 1/AU).

q

Perihelion distance (in AU).

e

Orbital eccentricity.

P

Orbital period (in years).

Peri.

The J2000.0 argument of perihelion (in degrees).

Node

The J2000.0 longitude of the ascending node (in degrees).

Incl.

The J2000.0 inclination (in degrees).

P and Q vectors

The vectors P and Q are an alternate form of representing the angular elements
Peri., Node and Incl. For an explanation of how to convert between the two
sets of quantities you are referred to standard celestial mechanics textbooks.

U

Uncertainty parameter.

Not all of these quantities will be given with every orbit, but enough information
will always be given to describe an orbit completely.

The following two quantities are not orbital elements but are generally given
with them.

H

Absolute visual magnitude. A table converting H to a diameter is available.
converting H

G

Slope parameter. For an explanation of the H,G magnitude system refer to
Application of Photometric Models to Asteroids, Bowell et al., in Asteroids
II, 524-556 (published by the University of Arizona Press, ISBN 0-8165-1123-3)
and the references therein.

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