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In astrodynamics, the orbital eccentricity of an astronomical object is a dimensionless parameter that determines the amount by which its orbit around another body deviates from a perfect circle. A value of 0 is a circular orbit , values between 0 and 1 form an elliptic orbit , 1 is a parabolic escape orbit (or capture orbit), and greater than ...
In orbital mechanics, the eccentric anomaly is an angular parameter that defines the position of a body that is moving along an elliptic Kepler orbit.The eccentric anomaly is one of three angular parameters ("anomalies") that define a position along an orbit, the other two being the true anomaly and the mean anomaly.
e is the eccentricity vector (a vector pointing towards the periapsis). In the case of equatorial orbits (which have no ascending node), the argument is strictly undefined. However, if the convention of setting the longitude of the ascending node Ω to 0 is followed, then the value of ω follows from the two-dimensional case: ω = a t a n 2 ( e ...
Orbital diagram of a quasi-satellite. A quasi-satellite, such as the one shown in this diagram, moves in a prograde orbit around the Sun, with the same orbital period (which is also called a year) as the planet it accompanies, but with a different (usually greater) orbital eccentricity. It appears, when seen from the planet, to revolve around ...
In two-body, Keplerian orbital mechanics, the equation of the center is the angular difference between the actual position of a body in its elliptical orbit and the position it would occupy if its motion were uniform, in a circular orbit of the same period.
Orbital eccentricity, in astrodynamics, a measure of the non-circularity of an orbit; Eccentric anomaly, the angle between the direction of periapsis and the current position of an object on its orbit; Eccentricity vector, in celestial mechanics, a dimensionless vector with direction pointing from apoapsis to periapsis
The rate of losing energy (averaged over a complete orbit) is given by [14] = (+) / (+ +) where e is the orbital eccentricity and a is the semimajor axis of the elliptical orbit. The angular brackets on the left-hand side of the equation represent the averaging over a single orbit.
Due to orbital eccentricity, the orbital velocity of Earth (in the Sun's rest frame) varies periodically during the year as the planet traverses its elliptic orbit and consequently the aberration also varies periodically, typically causing stars to appear to move in small ellipses.