Related:
Apsis,
Areostationary orbit,
Areosynchronous orbit,
Argument of periapsis,
Astrodynamics,
Astronomical unit,
Astronomy,
Barycentre,
Bi-elliptic transfer,
Box orbit,
Capture orbit,
Cartesian coordinate system,
Celestial coordinate system,
Circular orbit,
Coordinates (elementary mathematics),
Delta-v budget,
Direct motion,
Eccentric anomaly,
Eccentricity (mathematics),
Ellipse,
Elliptic orbit,
Elliptical orbit,
Empirical,
Ephemeris,
Epoch (astronomy),
Equatorial coordinate system,
Escape orbit,
Focus (geometry),
Frame of reference,
Geocentric orbit,
Geostationary orbit,
Geostationary transfer orbit,
Geosynchronous orbit,
Graveyard orbit,
Gravitational constant,
Gravity assist,
Gravity turn,
Ground track,
Halo orbit,
Heliocentric orbit,
Heliosynchronous orbit,
Highly elliptical orbit,
Hohmann transfer orbit,
Hyperbola,
Hyperbolic trajectory,
Inclination,
Inclined orbit,
Interplanetary Transport Network,
Isaac Newton,
Kepler's laws of planetary motion,
Lagrangian point,
Lissajous orbit,
List of orbits,
Longitude of the ascending node,
Low Earth orbit,
Low energy transfer,
Lunar orbit,
Mass,
Mean anomaly,
Mean longitude,
Medium Earth orbit,
Molniya orbit,
N-body problem,
Near equatorial orbit,
Non-inclined orbit,
Oberth effect,
Orbit,
Orbit equation,
Orbit of the Moon,
Orbit phasing,
Orbital eccentricity,
Orbital elements,
Orbital inclination change,
Orbital maneuver,
Orbital mechanics,
Orbital period,
Orbital speed,
Orbital state vectors,
Osculating orbit,
Parabola,
Parabolic trajectory,
Parking orbit,
Perturbation (astronomy),
Polar orbit,
Retrograde motion,
Semi-latus rectum,
Semi-minor axis,
Semi-synchronous orbit,
Solar system,
Space rendezvous,
Specific orbital energy,
Specific relative angular momentum,
Standard gravitational parameter,
Subsynchronous orbit,
Sun-synchronous orbit,
Synchronous orbit,
Transposition, docking, and extraction,
True anomaly,
True longitude,
Tundra orbit,
Two-body problem,
Two-line element set,
The major axis of an ellipse is its longest diameter, a line that runs through the centre and both foci, its ends being at the widest points of the shape. The semi-major axis is one half of the major axis, and thus runs from the centre, through a focus, and to the edge of the ellipse. For the special case of a circle, the semi-major axis is the radius.
In celestial mechanics, an apsis, plural apsides (pronounced /ˈæpsɨdiːz/) is the point of greatest or least distance of the elliptical orbit of an object from its center of attraction, which is usually the center of mass of the system.
An areostationary orbit (abbreviated ASO) is a circular areosynchronous orbit in the Martian equatorial plane about 17,000 km (10,600 miles) above the surface, any point on which revolves about Mars in the same direction and with the same period as the Martian surface. Although no artificial satellites have been placed so far in this orbit, it is of interest to some scientists foreseeing a future telecommunications network for the exploration of Mars. Areostationary orbit is a concept similar to Earth's geostationary orbit.
Areosynchronous orbits are class of synchronous orbits for artificial satellites around the planet Mars. As with all synchronous orbits, an areosynchronous orbit has an orbital period equal in length to Mars' sidereal day. A satellite in areosynchronous orbit does not necessarily maintain a fixed position in the sky as seen by an observer on the surface of Mars, however such a satellite will return to the same apparent position every Martian day.The argument of periapsis (also called argument of perifocus or argument of pericenter), symbolized as ω, is one of the orbital elements of an orbiting body. Specifically, ω is the angle between the orbit's periapsis (the point of closest approach to the central point) and the orbit's ascending node (the point where the body crosses the plane of reference from South to North). The angle is measured in the orbital plane and in the direction of motion. For specific types of orbits, words such as "perihelion" (for Sun-centered orbits), "perigee" (for Earth-centered orbits), "periastron" (for orbits around stars) and so on may replace the word "periapsis". See apsis for more information.
Orbital mechanics or astrodynamics is the application of ballistics and celestial mechanics to the practical problems concerning the motion of rockets and other spacecraft. The motion of these objects is usually calculated from Newton's laws of motion and Newton's law of universal gravitation. It is a core discipline within space mission design and control. Celestial mechanics treats more broadly the orbital dynamics of systems under the influence of gravity, including both spacecraft and natural astronomical bodies such as star systems, planets, moons, and comets. Orbital mechanics focuses on spacecraft trajectories, including orbital maneuvers, orbit plane changes, and interplanetary transfers, and is used by mission planners to predict the results of propulsive maneuvers. General relativity is a more exact theory than Newton's laws for calculating orbits, and is sometimes necessary for greater accuracy or in high-gravity situations (such as orbits close to the Sun).An astronomical unit (abbreviated as AU, au, a.u., or sometimes ua) is a unit of length equal to approximately 150 million kilometres (93 million miles). It is defined by the International Astronomical Union, and is defined as the mean distance between the Earth and the Sun over one Earth orbit.Astronomy is the scientific study of celestial objects (such as stars, planets, comets, nebulæ, star clusters and galaxies) and phenomena that originate outside the Earth's atmosphere (such as the cosmic background radiation). It is concerned with the evolution, physics, chemistry, meteorology, and motion of celestial objects, as well as the formation and development of the universe.