Orbital elements
Six orbital elements (see satellite orbit element ) describe the path of an astronomical object and its motion, the Kepler's laws in the gravitational field of a celestial body ( two-body problem ) obeys.
Two orbital elements describe the shape of the path, three elements describe the rail position in space and an element is the point at which the celestial body passes a certain point on the track. The most common path described with elements of the ellipse, on the occasion, the circulation time of the celestial body is given as the seventh track element.
The orbital elements of satellites included in addition to the six elements of an unperturbed motion on a Kepler ellipse usually more parameters with which perturbations are considered.
Form elements
The description of the shape of the trajectory requires two values , which define the shape and size:
- The numerical eccentricity ε.
- The semi-major axis a
Be derived from it:
- The semi- parameter p. With him there is the parametric representation of the Keplerian orbit: r ( φ ) = r (p, e).
- The Periapsisdistanz rmin: Distance from the apex of the main focal point.
- The eccentricity Φ: Φ = arc sin ( ε )
Layer elements
The location in space relative to a reference system is determined by three parameters:
- The inclination i: this is the angle of the plane of the path to the reference plane.
- The argument of the node ( node length) Ω: The angle from the coordinate origin of the reference plane to the ascending node ( at the intersection of the reference plane / train level).
- The argument of periapsis ω: the angle from the ascending node to periapsis ( zentrumsnächter point of the path ).
Time reference
The time reference defines the time zero point is fixed:
- Epoch t of the Periapsisdurchgangs of the body.
Derived quantities
- Mean motion n: average angular velocity of the mean anomaly M
The indication of orbital elements
The specified as a 6- tuple (p, e, i, Ω, ω, T ) is called the classical orbital elements. There are also other opportunities that are adapted to the particular case:
- (a, e, i, Ω, ω, T), suitable especially for comets and planets of the solar system method
- (a, e, i, Ω, ω, M) for the Pluto and the asteroids as they used the Astronomical Almanac.
- (a, e, i, Ω, π, L) are for example, the planetary theory VSOP 82 indirectly.
- (n, e, i, Ω, ω, M) of the NASA / NORAD Two Line Elements format system for artificial earth satellites