The **elements of an orbit** are the parameters needed to specify that orbit uniquely, given a model of two ideal masses obeying the Newtonian laws of motion and the inverse-square law of gravitational attraction. Because there are multiple ways of defining a motion, depending on which set of variable you choose to measure, there are several different ways of defining sets of orbital elements, each of which will define the same orbit. In physics, an orbit is the path that an object makes, around another object, whilst under the influence of a source of centripetal force, such as gravity. ...
In the article vector quantities are written in bold whereas scalar ones are in italics. ...
In physics, an inverse-square law is any physical law stating that some quantity is inversely proportional to the square of the distance from a point. ...
This article covers the physics of gravitation. ...
There are seven degrees of freedom in this model (time, position in 3-space at that time, velocity in 3-space at that time) so all sets of orbital elements have seven parameters. (*See also*: orbital state vectors). In astrodynamics or celestial dynamics orbital state vectors (sometimes State Vectors) are vectors of position () and velocity () that together with their time () ( epoch) uniquely determine the state of an orbiting body. ...
## Keplerian elements
Fig. 1: Diagram of Keplerian **Orbital parameters**. The traditionally used set of orbital elements is called the set of **Keplerian elements**, after Johannes Kepler and his Kepler's laws. The Keplerian elements are: Download high resolution version (1024x768, 45 KB)Orbit and orbital parameters Hmmm. ...
Download high resolution version (1024x768, 45 KB)Orbit and orbital parameters Hmmm. ...
Johannes Kepler Johannes Kepler (December 27, 1571 – November 15, 1630), a key figure in the scientific revolution, was a German astronomer, mathematician and astrologer. ...
Johannes Keplers primary contributions to astronomy/ astrophysics were the three laws of planetary motion. ...
Keplerian elements can be obtained from orbital state vectors using VEC2TLE software or by some direct computations. In astronomy, an epoch is a moment in time for which celestial coordinates or orbital elements are specified. ...
Inclination is one of the six orbital parameters describing the shape and orientation of a celestial orbit and is the angular distance of the orbital plane from the plane of the reference (usually planets equator or the ecliptic), stated in degrees. ...
The Longitude of the ascending node () is one of the orbital elements used to specify the orbit of an object in space. ...
In an orbit, the argument of periapsis () is the angle between the ascending node (the point where the orbiting body passes from the southern to the northern hemisphere) and the periapsis (the point of closest approach to the central body). ...
(This page refers to eccitricity in astrodynamics. ...
The orbital period is the time it takes a planet (or another object) to make one full orbit. ...
In astrodynamics or celestial dynamics mean longitude of an orbiting body is . ...
In the study of orbital dynamics the mean anomaly is a measure of time, specific to the orbiting body p, which is a multiple of 2π radians at and only at periapsis. ...
In astrodynamics or celestial dynamics orbital state vectors (sometimes State Vectors) are vectors of position () and velocity () that together with their time () ( epoch) uniquely determine the state of an orbiting body. ...
In astrodynamics or celestial dynamics orbital state vectors (sometimes State Vectors) are vectors of position () and velocity () that together with their time () ( epoch) uniquely determine the state of an orbiting body. ...
Fig. 2: Keplerian **orbital parametres**. Other orbital parameters, such as the semi-major axis, can then be calculated from the Keplerian elements. In many cases, the semi-major axis is used as an orbital element instead of period. The elements can be seen as defining the orbit by degrees: Orbital parametres, illustrated. ...
Orbital parametres, illustrated. ...
In mathematics, an ellipse (from the Greek for absence) is a curve where the sum of the distances from any point on the curve to two fixed points is constant. ...
- The semi-major axis (or the period, interchangeably) fixes the size of the orbit.
- The eccentricity fixes its shape.
- The inclination (orange in Fig. 2) and longitude of the ascending node (green) fix its plane.
- The argument of perihelion (blue) orients the orbit within its plane.
- The epoch (or mean anomaly, interchangeably) (red) fixes the object in time on its orbit.
Because the simple Newtonian model of orbital motion of idealized points in free space is not exact, the orbital elements of real objects tend to change over time. For artificial satellites grazing the fringes of the atmosphere, an eighth parameter (" drag") may be added. For the planets and moons it is more usual simply to add a time term to the elements. Atmospheric drag drag is a form of drag . ...
## Two line elements Keplerian elements parameters can be encoded as text in a number of formats. The most common of them is the NASA/NORAD **"two-line elements"** (TLE) format, originally designed for use with 80-column punched cards, but still in use because it is the most common format, and works as well as any other. Reference: - Explanatory Supplement to the Astronomical Almanac. 1992. K. P. Seidelmann, Ed., University Science Books, Mill Valley, California.
## See also An ephemeris (plural: ephemerides) (from the Greek word ephemeros= daily) was, traditionally, a table providing the positions (given in a Cartesian coordinate system, or in right ascension and declination or, for astrologers, in longitude along the zodiacal ecliptic), of the Sun, the Moon, and the planets in the sky at...
In astrodynamics or celestial dynamics orbital state vectors (sometimes State Vectors) are vectors of position () and velocity () that together with their time () ( epoch) uniquely determine the state of an orbiting body. ...
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