Celestial mechanics

Analemma is a term in astronomy used to describe the plot of the positions of the Sun on the celestial sphere at the same time of day (at approximately 24 hour intervals) and from the same location on Earth on successive days through the calendar year. This appears as a figure eight. If the course of the Earth around the sun were a precise circle and if the Earth's polar axis stood perpendicular to the plane of its orbit, the Sun would always appear at the same point in the sky at the same time of day throughout the year and the analemma would be a dot. If the orbit were circular, but the polar axis tilted as it is, the northern and southern lobes of the figure of eight would be equal in size; if the polar axis were not tilted but the orbit had its current eccentricity then the analemma would be a straight east-to-west line. It is difficult but possible to construct an analemma by taking a photograph of the sun each day of the year at the same time and place and with a camera positioned in exactly the same ...more on Wikipedia about "Analemma"

: This article is about several astronomical terms (apogee & perigee, aphelion & perihelion, generic equivalents based on apsis, and related but rarer terms). In architecture, apsis is a synonym for apse. ...more on Wikipedia about "Apsis"

An areostationary orbit (abbreviated ASO) is a circular areosynchronous orbit in the Martian equatorial plane 11,000 km 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 forseeing a future telecommunications network for the exploration of Mars. Areostationary orbit is a concept similar to Earth's geostationary orbit. ...more on Wikipedia about "Areostationary orbit"

Areostationary satellite is an artificial satellite in areostationary orbit (i.e. prograde synchronous orbit in equatorial plane around Mars). ...more on Wikipedia about "Areostationary satellite"

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. ...more on Wikipedia about "Areosynchronous orbit"

Areosynchronous satellite is an artificial satellite in areosynchronous orbit (i.e. synchronous orbits around Mars). ...more on Wikipedia about "Areosynchronous satellite"

In an orbit, the argument of periapsis (ω) 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), measured in the body's orbital plane and in its direction of motion. It is undefined for equatorial orbits, where there is no defined ascending node, and for circular orbits, where there is no defined periapsis. The argument of periapsis is often called the argument of perihelion for objects orbiting the sun, and the argument of perigee for objects orbiting planets, such as satellites. ...more on Wikipedia about "Argument of periapsis"

The argument of the perihelion is one of the orbital elements describing a body in a Sun-centered orbit (e.g., a planet). It is the angle between the ascending node and the perihelion, measured in the orbital plane. Adding it to the longitude of the ascending node gives the longitude of perihelion of the body in its orbit around the Sun. ...more on Wikipedia about "Argument of the perihelion"

The astronomical unit (AU or au or a.u. or sometimes ua) is a unit of distance, approximately equal to the mean distance between Earth and Sun. The currently accepted value of the AU is 149 597 870 691 ± 30 metres (about 150 million kilometres or 93 million miles). ...more on Wikipedia about "Astronomical unit"

The autumnal equinox (or fall equinox) marks the beginning of astronomical autumn. It occurs during the month of September in the Northern Hemisphere, and during March in the Southern Hemisphere. In Chinese culture it marks the middle of autumn. At the same moment that the autumnal equinox occurs in one hemisphere, it is the time of the vernal equinox in the other hemisphere. ...more on Wikipedia about "Autumnal equinox"

In astronautics and aerospace engineering, the Bi-elliptic transfer is an orbital maneuver that moves a spacecraft from one orbit to another and may, in certain situations require less delta-v then a Hohmann transfer. ...more on Wikipedia about "Bi-elliptic transfer"

A binary system is an astronomy term referring to two objects in space, usually stars, which are so close that their gravitational forces attract one another into a mutual orbit. Astronomers find that more than 50% of stars are binary stars. A multiple system is like a binary system but consists of three or more objects. ...more on Wikipedia about "Binary system (astronomy)"

In stellar dynamics a box orbit refers to a particular type of orbit which can be seen in triaxial systems, that is, systems which do not possess a symmetry around any of its axes. They contrast with the loop orbits which are observed in spherically symmetric or axisymmetric systems. ...more on Wikipedia about "Box orbit"

The celestial equator is a great circle on the imaginary celestial sphere, which is actually the plane of the terrestrial equator extended out into the universe (i.e., it could be constructed by extrapolating the Earth's equator until it touches the celestial sphere). The celestial equator is inclined by ~23.5°, with respect to the ecliptic plane; a result of axial tilt. Celestial objects near the celestial equator are visible worldwide, but they culminate the highest in the sky in the tropics. ...more on Wikipedia about "Celestial equator"

Celestial mechanics is a division of astronomy dealing with the motions and gravitational effects of celestial objects. The field applies principles of physics, historically Newtonian mechanics, to astronomical objects such as stars and planets. ...more on Wikipedia about "Celestial mechanics"

In astrodynamics a central body ( $m_1\,$ ) is a body that is being orbited by orbiting body( $m_2\,$ ). Under standard assumptions in astrodynamics: ...more on Wikipedia about "Central body"

In astrodynamics a characteristic energy ( $C_3\,\!$ ) is a measure of the energy required for an interplanetary mission that requires attaining an excess orbital velocity over an escape velocity required for additional orbital maneuvers. The unit of the characteristic energy is km² s^-2. ...more on Wikipedia about "Characteristic energy"

:For other meanings of the term "orbit", see orbit (disambiguation) ...more on Wikipedia about "Circular orbit"

In cosmology, dark matter refers to hypothetical matter particles, of unknown composition, that do not emit or reflect enough electromagnetic radiation to be detected directly, but whose presence can be inferred from gravitational effects on visible matter such as stars and galaxies. The dark matter hypothesis aims to explain several anomalous astronomical observations, such as anomalies in the rotational speed of galaxies (the galaxy rotation problem). Estimates of the amount of matter present in galaxies, based on gravitational effects, consistently suggest that there is far more matter than is directly observable. The existence of dark matter would also resolve a number of inconsistencies in the Big Bang theory, and is crucial for structure formation. ...more on Wikipedia about "Dark matter"

In general physics, delta-v is simply the change in velocity. ...more on Wikipedia about "Delta-v"

The eccentric anomaly is the angle between the direction of periapsis and the current position of an object on its orbit, projected onto the ellipse's circumscribing circle perpendicularly to the major axis, measured at the centre of the ellipse. In the diagram below, it is E (the angle zcx). ...more on Wikipedia about "Eccentric anomaly"

In astrodynamics, under standard assumptions any orbit must be of conic section shape. The eccentricity of this conic section, the orbit's eccentricity, is an important parameter of the orbit that defines its absolute shape. Eccentricity may be interpreted as a measure of how much this shape deviates from a circle. ...more on Wikipedia about "Eccentricity (orbit)"

In astrodynamics the eccentricity vector of a conic section orbit is the vector pointing towards the periapsis and with length equal to the orbit's scalar eccentricity. ...more on Wikipedia about "Eccentricity vector"

Eclipitic orbit is an orbit with inclination to the plane of reference (i.d. ecliptic) equal to zero. ...more on Wikipedia about "Ecliptic orbit"

Under standard assumptions the orbital velocity ( $v\,$ ) of a body traveling along elliptic orbit can be computed as: ...more on Wikipedia about "Elliptic orbit"

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