List of orbits
Encyclopedia
Orbit
In physics, an orbit is the gravitationally curved path of an object around a point in space, for example the orbit of a planet around the center of a star system, such as the Solar System...
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Centric classifications
- Galactocentric orbitGalactic CenterThe Galactic Center is the rotational center of the Milky Way galaxy. It is located at a distance of 8.33±0.35 kpc from the Earth in the direction of the constellations Sagittarius, Ophiuchus, and Scorpius where the Milky Way appears brightest...
: An orbit about the center of a galaxyGalaxyA galaxy is a massive, gravitationally bound system that consists of stars and stellar remnants, an interstellar medium of gas and dust, and an important but poorly understood component tentatively dubbed dark matter. The word galaxy is derived from the Greek galaxias , literally "milky", a...
. The SunSunThe Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...
follows this type of orbit about the galactic centerGalactic CenterThe Galactic Center is the rotational center of the Milky Way galaxy. It is located at a distance of 8.33±0.35 kpc from the Earth in the direction of the constellations Sagittarius, Ophiuchus, and Scorpius where the Milky Way appears brightest...
of the Milky WayMilky WayThe Milky Way is the galaxy that contains the Solar System. This name derives from its appearance as a dim un-resolved "milky" glowing band arching across the night sky...
. - Heliocentric orbitHeliocentric orbitA heliocentric orbit is an orbit around the Sun. All planets, comets, and asteroids in our Solar System are in such orbits, as are many artificial probes and pieces of debris. The moons of planets in the Solar System, by contrast, are not in heliocentric orbits as they orbit their respective planet...
: An orbitOrbitIn physics, an orbit is the gravitationally curved path of an object around a point in space, for example the orbit of a planet around the center of a star system, such as the Solar System...
around the SunSunThe Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...
. In our Solar SystemSolar SystemThe Solar System consists of the Sun and the astronomical objects gravitationally bound in orbit around it, all of which formed from the collapse of a giant molecular cloud approximately 4.6 billion years ago. The vast majority of the system's mass is in the Sun...
, all planets, comets, and asteroids are in such orbits, as are many artificial satellites and pieces of space debrisSpace debrisSpace debris, also known as orbital debris, space junk, and space waste, is the collection of objects in orbit around Earth that were created by humans but no longer serve any useful purpose. These objects consist of everything from spent rocket stages and defunct satellites to erosion, explosion...
. Moons by contrast are not in a heliocentric orbitHeliocentric orbitA heliocentric orbit is an orbit around the Sun. All planets, comets, and asteroids in our Solar System are in such orbits, as are many artificial probes and pieces of debris. The moons of planets in the Solar System, by contrast, are not in heliocentric orbits as they orbit their respective planet...
but rather orbit their parent planet. - Geocentric orbitGeocentric orbitA geocentric orbit involves any object orbiting the Earth, such as the Moon or artificial satellites. Currently there are approximately 2,465 artificial satellites orbiting the Earth and 6,216 pieces of space debris as tracked by the Goddard Space Flight Center...
: An orbit around the planet EarthEarthEarth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets...
, such as the MoonMoonThe Moon is Earth's only known natural satellite,There are a number of near-Earth asteroids including 3753 Cruithne that are co-orbital with Earth: their orbits bring them close to Earth for periods of time but then alter in the long term . These are quasi-satellites and not true moons. For more...
or artificial satellites. - Areocentric orbitAreocentric orbitAn areocentric orbit is an orbit around the planet Mars. The Moon, by similarity, is in a geocentric orbit around Earth.The areo- prefix is derived from the ancient Greek word Ares which is the personification of the planet Mars in Greek mythology....
: An orbit around the planet MarsMarsMars is the fourth planet from the Sun in the Solar System. The planet is named after the Roman god of war, Mars. It is often described as the "Red Planet", as the iron oxide prevalent on its surface gives it a reddish appearance...
, such as moons or artificial satellites. - Lunar orbitLunar orbitIn astronomy, lunar orbit refers to the orbit of an object around the Moon.As used in the space program, this refers not to the orbit of the Moon about the Earth, but to orbits by various manned or unmanned spacecraft around the Moon...
(also selenocentric orbit): An orbit around the Earth's moonMoonThe Moon is Earth's only known natural satellite,There are a number of near-Earth asteroids including 3753 Cruithne that are co-orbital with Earth: their orbits bring them close to Earth for periods of time but then alter in the long term . These are quasi-satellites and not true moons. For more...
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Altitude classifications for geocentric orbits
- Low Earth orbitLow Earth orbitA low Earth orbit is generally defined as an orbit within the locus extending from the Earth’s surface up to an altitude of 2,000 km...
(LEO): Geocentric orbitGeocentric orbitA geocentric orbit involves any object orbiting the Earth, such as the Moon or artificial satellites. Currently there are approximately 2,465 artificial satellites orbiting the Earth and 6,216 pieces of space debris as tracked by the Goddard Space Flight Center...
s with altitudes up to 2,000 kmKMKM, Km, or km may stand for:*Kilometre *Kernel methods*Kettle Moraine High School*Khmer language *Kuomintang , a centre-right political party in the Republic of China on Taiwan...
(0–1,240 mileMileA mile is a unit of length, most commonly 5,280 feet . The mile of 5,280 feet is sometimes called the statute mile or land mile to distinguish it from the nautical mile...
s). - Medium Earth orbitMedium Earth OrbitMedium Earth orbit , sometimes called intermediate circular orbit , is the region of space around the Earth above low Earth orbit and below geostationary orbit ....
(MEO): Geocentric orbitGeocentric orbitA geocentric orbit involves any object orbiting the Earth, such as the Moon or artificial satellites. Currently there are approximately 2,465 artificial satellites orbiting the Earth and 6,216 pieces of space debris as tracked by the Goddard Space Flight Center...
s ranging in altitude from 2,000 kmKMKM, Km, or km may stand for:*Kilometre *Kernel methods*Kettle Moraine High School*Khmer language *Kuomintang , a centre-right political party in the Republic of China on Taiwan...
(1,240 mileMileA mile is a unit of length, most commonly 5,280 feet . The mile of 5,280 feet is sometimes called the statute mile or land mile to distinguish it from the nautical mile...
s) to just below geosynchronous orbitGeosynchronous orbitA geosynchronous orbit is an orbit around the Earth with an orbital period that matches the Earth's sidereal rotation period...
at 35,786 kmKMKM, Km, or km may stand for:*Kilometre *Kernel methods*Kettle Moraine High School*Khmer language *Kuomintang , a centre-right political party in the Republic of China on Taiwan...
(22,240 mileMileA mile is a unit of length, most commonly 5,280 feet . The mile of 5,280 feet is sometimes called the statute mile or land mile to distinguish it from the nautical mile...
s). Also known as an intermediate circular orbit. - Geostationary orbitGeostationary orbitA geostationary orbit is a geosynchronous orbit directly above the Earth's equator , with a period equal to the Earth's rotational period and an orbital eccentricity of approximately zero. An object in a geostationary orbit appears motionless, at a fixed position in the sky, to ground observers...
(GEO): The orbit around Earth matching Earth's sidereal rotation period. All geostationary orbits have a semi-major axisSemi-major axisThe 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...
of 42164 km (26,200 mi). - High Earth orbitHigh Earth orbitA High Earth Orbit is a geocentric orbit whose apogee lies above that of a geosynchronous orbit .Highly Elliptical Orbits are a subset of High Earth Orbits.-Examples of satellites in High Earth Orbit:...
: Geocentric orbitGeocentric orbitA geocentric orbit involves any object orbiting the Earth, such as the Moon or artificial satellites. Currently there are approximately 2,465 artificial satellites orbiting the Earth and 6,216 pieces of space debris as tracked by the Goddard Space Flight Center...
s above the altitude of geosynchronous orbitGeosynchronous orbitA geosynchronous orbit is an orbit around the Earth with an orbital period that matches the Earth's sidereal rotation period...
35,786 kmKMKM, Km, or km may stand for:*Kilometre *Kernel methods*Kettle Moraine High School*Khmer language *Kuomintang , a centre-right political party in the Republic of China on Taiwan...
(22,240 mileMileA mile is a unit of length, most commonly 5,280 feet . The mile of 5,280 feet is sometimes called the statute mile or land mile to distinguish it from the nautical mile...
s).
Inclination classifications
- Inclined orbitInclined orbitA satellite is said to occupy an inclined orbit around the Earth if the orbit exhibits an angle other than zero degrees with the equatorial plane. This angle is called the orbit's inclination...
: An orbit whose inclinationInclinationInclination in general is the angle between a reference plane and another plane or axis of direction.-Orbits:The inclination is one of the six orbital parameters describing the shape and orientation of a celestial orbit...
in reference to the equatorial plane is not 0.- Polar orbitPolar orbitA polar orbit is an orbit in which a satellite passes above or nearly above both poles of the body being orbited on each revolution. It therefore has an inclination of 90 degrees to the equator...
: An orbitOrbitIn physics, an orbit is the gravitationally curved path of an object around a point in space, for example the orbit of a planet around the center of a star system, such as the Solar System...
that passes above or nearly above both poles of the planet on each revolution. Therefore it has an inclinationInclinationInclination in general is the angle between a reference plane and another plane or axis of direction.-Orbits:The inclination is one of the six orbital parameters describing the shape and orientation of a celestial orbit...
of (or very close to) 90 degreeDegree (angle)A degree , usually denoted by ° , is a measurement of plane angle, representing 1⁄360 of a full rotation; one degree is equivalent to π/180 radians...
s. - Polar Sun-synchronous orbitSun-synchronous orbitA Sun-synchronous orbit is a geocentric orbit which combines altitude and inclination in such a way that an object on that orbit ascends or descends over any given point of the Earth's surface at the same local mean solar time. The surface illumination angle will be nearly the same every time...
(SSO): A nearly polar orbitPolar orbitA polar orbit is an orbit in which a satellite passes above or nearly above both poles of the body being orbited on each revolution. It therefore has an inclination of 90 degrees to the equator...
that passes the equatorEquatorAn equator is the intersection of a sphere's surface with the plane perpendicular to the sphere's axis of rotation and containing the sphere's center of mass....
at the same local solar timeSolar timeSolar time is a reckoning of the passage of time based on the Sun's position in the sky. The fundamental unit of solar time is the day. Two types of solar time are apparent solar time and mean solar time .-Introduction:...
on every pass. Useful for imageImageAn image is an artifact, for example a two-dimensional picture, that has a similar appearance to some subject—usually a physical object or a person.-Characteristics:...
-taking satellites because shadowShadowA shadow is an area where direct light from a light source cannot reach due to obstruction by an object. It occupies all of the space behind an opaque object with light in front of it. The cross section of a shadow is a two-dimensional silhouette, or reverse projection of the object blocking the...
s will be the same on every pass.
- Polar orbit
- Non-inclined orbit: An orbit whose inclinationInclinationInclination in general is the angle between a reference plane and another plane or axis of direction.-Orbits:The inclination is one of the six orbital parameters describing the shape and orientation of a celestial orbit...
is equal to zero with respect to some plane of referencePlane of referenceA term used in celestial mechanics, the plane of reference is the plane by means of which orbital elements are defined. The two main orbital elements that are measured with respect to the plane of reference are the inclination and the longitude of the ascending node.Depending on the type of body...
.- Ecliptical orbit: A non-inclined orbit with respect to the eclipticEclipticThe ecliptic is the plane of the earth's orbit around the sun. In more accurate terms, it is the intersection of the celestial sphere with the ecliptic plane, which is the geometric plane containing the mean orbit of the Earth around the Sun...
. - Equatorial orbit: A non-inclined orbit with respect to the equatorEquatorAn equator is the intersection of a sphere's surface with the plane perpendicular to the sphere's axis of rotation and containing the sphere's center of mass....
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- Ecliptical orbit: A non-inclined orbit with respect to the ecliptic
- Near equatorial orbitNear equatorial orbitA near-equatorial orbit is an orbit that lies close to the equatorial plane of the object orbited. This orbit allows for rapid revisit times of near-equatorial ground sites.- See also :* List of orbits...
: An orbit whose inclination with respect to the equatorial plane is nearly zero. This orbit allows for rapid revisit times (for a single orbiting spacecraft) of near equatorial ground sites.
Eccentricity classifications
There are two types of orbits. Closed (periodic) orbits, and open (escape) orbits. Circular and elliptical orbits are closed. Parabolic and hyperbolic orbits are open. Radial orbits can be either open or closed.- Circular orbitCircular orbitA circular orbit is the orbit at a fixed distance around any point by an object rotating around a fixed axis.Below we consider a circular orbit in astrodynamics or celestial mechanics under standard assumptions...
: An orbitOrbitIn physics, an orbit is the gravitationally curved path of an object around a point in space, for example the orbit of a planet around the center of a star system, such as the Solar System...
that has an eccentricityOrbital eccentricityThe orbital eccentricity of an astronomical body is the amount by which its orbit deviates from a perfect circle, where 0 is perfectly circular, and 1.0 is a parabola, and no longer a closed orbit...
of 0 and whose path traces a circleCircleA circle is a simple shape of Euclidean geometry consisting of those points in a plane that are a given distance from a given point, the centre. The distance between any of the points and the centre is called the radius....
. - Elliptic orbitElliptic orbitIn astrodynamics or celestial mechanics an elliptic orbit is a Kepler orbit with the eccentricity less than 1; this includes the special case of a circular orbit, with eccentricity equal to zero. In a stricter sense, it is a Kepler orbit with the eccentricity greater than 0 and less than 1 . In a...
: An orbitOrbitIn physics, an orbit is the gravitationally curved path of an object around a point in space, for example the orbit of a planet around the center of a star system, such as the Solar System...
with an eccentricityOrbital eccentricityThe orbital eccentricity of an astronomical body is the amount by which its orbit deviates from a perfect circle, where 0 is perfectly circular, and 1.0 is a parabola, and no longer a closed orbit...
greater than 0 and less than 1 whose orbit traces the path of an ellipseEllipseIn geometry, an ellipse is a plane curve that results from the intersection of a cone by a plane in a way that produces a closed curve. Circles are special cases of ellipses, obtained when the cutting plane is orthogonal to the cone's axis...
.- Geostationary or Geosynchronous transfer orbitGeostationary transfer orbitA geosynchronous transfer orbit or geostationary transfer orbit is a Hohmann transfer orbit used to reach geosynchronous or geostationary orbit....
: An elliptic orbitElliptic orbitIn astrodynamics or celestial mechanics an elliptic orbit is a Kepler orbit with the eccentricity less than 1; this includes the special case of a circular orbit, with eccentricity equal to zero. In a stricter sense, it is a Kepler orbit with the eccentricity greater than 0 and less than 1 . In a...
where the perigeePerigeePerigee is the point at which an object makes its closest approach to the Earth.. Often the term is used in a broader sense to define the point in an orbit where the orbiting body is closest to the body it orbits. The opposite is the apogee, the farthest or highest point.The Greek prefix "peri"...
is at the altitudeAltitudeAltitude or height is defined based on the context in which it is used . As a general definition, altitude is a distance measurement, usually in the vertical or "up" direction, between a reference datum and a point or object. The reference datum also often varies according to the context...
of a Low Earth OrbitLow Earth orbitA low Earth orbit is generally defined as an orbit within the locus extending from the Earth’s surface up to an altitude of 2,000 km...
(LEO) and the apogee at the altitudeAltitudeAltitude or height is defined based on the context in which it is used . As a general definition, altitude is a distance measurement, usually in the vertical or "up" direction, between a reference datum and a point or object. The reference datum also often varies according to the context...
of a geostationary orbitGeostationary orbitA geostationary orbit is a geosynchronous orbit directly above the Earth's equator , with a period equal to the Earth's rotational period and an orbital eccentricity of approximately zero. An object in a geostationary orbit appears motionless, at a fixed position in the sky, to ground observers...
. - Hohmann transfer orbitHohmann transfer orbitIn orbital mechanics, the Hohmann transfer orbit is an elliptical orbit used to transfer between two circular orbits, typically both in the same plane....
: An orbital maneuverOrbital maneuverIn spaceflight, an orbital maneuver is the use of propulsion systems to change the orbit of a spacecraft.For spacecraft far from Earth—for example those in orbits around the Sun—an orbital maneuver is called a deep-space maneuver .-delta-v:...
that moves a spacecraftSpacecraftA spacecraft or spaceship is a craft or machine designed for spaceflight. Spacecraft are used for a variety of purposes, including communications, earth observation, meteorology, navigation, planetary exploration and transportation of humans and cargo....
from one circular orbitCircular orbitA circular orbit is the orbit at a fixed distance around any point by an object rotating around a fixed axis.Below we consider a circular orbit in astrodynamics or celestial mechanics under standard assumptions...
to another using two engine impulses. This maneuver was named after Walter HohmannWalter HohmannWalter Hohmann was a German engineer who made an important contribution to the understanding of orbital dynamics. In a book published in 1925, Hohmann demonstrated a very fuel-efficient path to move a spacecraft between two different orbits, now called a Hohmann transfer orbit. He received his Ph.D...
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- Geostationary or Geosynchronous transfer orbit
- Parabolic orbit: An orbitOrbitIn physics, an orbit is the gravitationally curved path of an object around a point in space, for example the orbit of a planet around the center of a star system, such as the Solar System...
with the eccentricity equal to 1. Such an orbit also has a velocityVelocityIn physics, velocity is speed in a given direction. Speed describes only how fast an object is moving, whereas velocity gives both the speed and direction of the object's motion. To have a constant velocity, an object must have a constant speed and motion in a constant direction. Constant ...
equal to the escape velocityEscape velocityIn physics, escape velocity is the speed at which the kinetic energy plus the gravitational potential energy of an object is zero gravitational potential energy is negative since gravity is an attractive force and the potential is defined to be zero at infinity...
and therefore will escape the gravitational pull of the planetPlanetA planet is a celestial body orbiting a star or stellar remnant that is massive enough to be rounded by its own gravity, is not massive enough to cause thermonuclear fusion, and has cleared its neighbouring region of planetesimals.The term planet is ancient, with ties to history, science,...
. If the speed of a parabolic orbit is increased it will become a hyperbolic orbit.- Escape orbit: A parabolic orbit where the object has escape velocityEscape velocityIn physics, escape velocity is the speed at which the kinetic energy plus the gravitational potential energy of an object is zero gravitational potential energy is negative since gravity is an attractive force and the potential is defined to be zero at infinity...
and is moving directly away from the planetPlanetA planet is a celestial body orbiting a star or stellar remnant that is massive enough to be rounded by its own gravity, is not massive enough to cause thermonuclear fusion, and has cleared its neighbouring region of planetesimals.The term planet is ancient, with ties to history, science,...
. - Capture orbit: A parabolic orbit where the object has escape velocityEscape velocityIn physics, escape velocity is the speed at which the kinetic energy plus the gravitational potential energy of an object is zero gravitational potential energy is negative since gravity is an attractive force and the potential is defined to be zero at infinity...
and is moving directly toward the planetPlanetA planet is a celestial body orbiting a star or stellar remnant that is massive enough to be rounded by its own gravity, is not massive enough to cause thermonuclear fusion, and has cleared its neighbouring region of planetesimals.The term planet is ancient, with ties to history, science,...
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- Escape orbit: A parabolic orbit where the object has escape velocity
- Hyperbolic orbit: An orbitOrbitIn physics, an orbit is the gravitationally curved path of an object around a point in space, for example the orbit of a planet around the center of a star system, such as the Solar System...
with the eccentricity greater than or equal to 1. Such an orbit also has a velocityVelocityIn physics, velocity is speed in a given direction. Speed describes only how fast an object is moving, whereas velocity gives both the speed and direction of the object's motion. To have a constant velocity, an object must have a constant speed and motion in a constant direction. Constant ...
in excess of the escape velocityEscape velocityIn physics, escape velocity is the speed at which the kinetic energy plus the gravitational potential energy of an object is zero gravitational potential energy is negative since gravity is an attractive force and the potential is defined to be zero at infinity...
and as such, will escape the gravitational pull of the planetPlanetA planet is a celestial body orbiting a star or stellar remnant that is massive enough to be rounded by its own gravity, is not massive enough to cause thermonuclear fusion, and has cleared its neighbouring region of planetesimals.The term planet is ancient, with ties to history, science,...
and continue to travel infinitely until it is acted upon by another body with sufficient gravitational force. - Radial orbit: An orbit with zero angular momentumAngular momentumIn physics, angular momentum, moment of momentum, or rotational momentum is a conserved vector quantity that can be used to describe the overall state of a physical system...
and eccentricity equal to 1. The two objects move directly towards or away from each other in a straight-line.- Radial elliptic orbit: A closed elliptic orbitElliptic orbitIn astrodynamics or celestial mechanics an elliptic orbit is a Kepler orbit with the eccentricity less than 1; this includes the special case of a circular orbit, with eccentricity equal to zero. In a stricter sense, it is a Kepler orbit with the eccentricity greater than 0 and less than 1 . In a...
where the object is moving at less than the escape velocityEscape velocityIn physics, escape velocity is the speed at which the kinetic energy plus the gravitational potential energy of an object is zero gravitational potential energy is negative since gravity is an attractive force and the potential is defined to be zero at infinity...
. This is an elliptic orbit with semi-minor axis = 0 and eccentricity = 1. Although the eccentricity is 1, this is not a parabolic orbit. - Radial parabolic orbit: An open parabolic orbit where the object is moving at the escape velocityEscape velocityIn physics, escape velocity is the speed at which the kinetic energy plus the gravitational potential energy of an object is zero gravitational potential energy is negative since gravity is an attractive force and the potential is defined to be zero at infinity...
. - Radial hyperbolic orbit: An open hyperbolic orbit where the object is moving at greater than the escape velocityEscape velocityIn physics, escape velocity is the speed at which the kinetic energy plus the gravitational potential energy of an object is zero gravitational potential energy is negative since gravity is an attractive force and the potential is defined to be zero at infinity...
. This is a hyperbolic orbit with semi-minor axis = 0 and eccentricity = 1. Although the eccentricity is 1, this is not a parabolic orbit.
- Radial elliptic orbit: A closed elliptic orbit
Synchronous classifications
- Synchronous orbitSynchronous orbitA synchronous orbit is an orbit in which an orbiting body has a period equal to the average rotational period of the body being orbited , and in the same direction of rotation as that body.-Properties:...
: An orbit whose periodOrbital periodThe orbital period is the time taken for a given object to make one complete orbit about another object.When mentioned without further qualification in astronomy this refers to the sidereal period of an astronomical object, which is calculated with respect to the stars.There are several kinds of...
is a rational multiple of the average rotational period of the body being orbited and in the same direction of rotation as that body. This means the track of the satellite, as seen from the central body, will repeat exactly after a fixed number of orbits. In practice, only 1:1 ratio (geosynchronous) and 1:2 ratios (semi-synchronous) are common.
- Geosynchronous orbitGeosynchronous orbitA geosynchronous orbit is an orbit around the Earth with an orbital period that matches the Earth's sidereal rotation period...
(GSO): An orbit around the Earth with a period equal to one sidereal day, which is Earth's average rotational period of 23 hourHourThe hour is a unit of measurement of time. In modern usage, an hour comprises 60 minutes, or 3,600 seconds...
s, 56 minuteMinuteA minute is a unit of measurement of time or of angle. The minute is a unit of time equal to 1/60th of an hour or 60 seconds. In the UTC time scale, a minute on rare occasions has 59 or 61 seconds; see leap second. The minute is not an SI unit; however, it is accepted for use with SI units...
s, 4.091 secondSecondThe second is a unit of measurement of time, and is the International System of Units base unit of time. It may be measured using a clock....
s. For a nearly circular orbit, this implies an altitude of approximately 35,786 km (22,240 miles). If both the inclination and eccentricity are zero, then the satellite will appear stationary from the ground. If not, then each day the satellite traces out an analemmaAnalemmaIn astronomy, an analemma is a curve representing the angular offset of a celestial body from its mean position on the celestial sphere as viewed from another celestial body relative to the viewing body's celestial equator...
(figure 8) in the sky, as seen from the ground.- Geostationary orbitGeostationary orbitA geostationary orbit is a geosynchronous orbit directly above the Earth's equator , with a period equal to the Earth's rotational period and an orbital eccentricity of approximately zero. An object in a geostationary orbit appears motionless, at a fixed position in the sky, to ground observers...
(GEO): A circular geosynchronous orbitGeosynchronous orbitA geosynchronous orbit is an orbit around the Earth with an orbital period that matches the Earth's sidereal rotation period...
with an inclinationInclinationInclination in general is the angle between a reference plane and another plane or axis of direction.-Orbits:The inclination is one of the six orbital parameters describing the shape and orientation of a celestial orbit...
of zero. To an observer on the ground this satellite appears as a fixed point in the sky.- Clarke orbit: Another name for a geostationary orbitGeostationary orbitA geostationary orbit is a geosynchronous orbit directly above the Earth's equator , with a period equal to the Earth's rotational period and an orbital eccentricity of approximately zero. An object in a geostationary orbit appears motionless, at a fixed position in the sky, to ground observers...
. Named after the writer Arthur C. ClarkeArthur C. ClarkeSir Arthur Charles Clarke, CBE, FRAS was a British science fiction author, inventor, and futurist, famous for his short stories and novels, among them 2001: A Space Odyssey, and as a host and commentator in the British television series Mysterious World. For many years, Robert A. Heinlein,...
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- Clarke orbit: Another name for a geostationary orbit
- Geostationary orbit
- Tundra orbitTundra orbitTundra orbit is a type of highly elliptical geosynchronous orbit with a high inclination and an orbital period of one sidereal day . A satellite placed in this orbit spends most of its time over a chosen area of the Earth, a phenomenon known as apogee dwell...
: A synchronous but highly elliptic orbitElliptic orbitIn astrodynamics or celestial mechanics an elliptic orbit is a Kepler orbit with the eccentricity less than 1; this includes the special case of a circular orbit, with eccentricity equal to zero. In a stricter sense, it is a Kepler orbit with the eccentricity greater than 0 and less than 1 . In a...
with inclinationInclinationInclination in general is the angle between a reference plane and another plane or axis of direction.-Orbits:The inclination is one of the six orbital parameters describing the shape and orientation of a celestial orbit...
of 63.4° and orbital periodOrbital periodThe orbital period is the time taken for a given object to make one complete orbit about another object.When mentioned without further qualification in astronomy this refers to the sidereal period of an astronomical object, which is calculated with respect to the stars.There are several kinds of...
of one sidereal day (23 hours, 56 minutes for the Earth). Such a satellite spends most of its time over a designated area of the planetPlanetA planet is a celestial body orbiting a star or stellar remnant that is massive enough to be rounded by its own gravity, is not massive enough to cause thermonuclear fusion, and has cleared its neighbouring region of planetesimals.The term planet is ancient, with ties to history, science,...
. The particular inclination keeps the perigee shift small. - Semi-synchronous orbitSemi-synchronous OrbitSemi-Synchronous Orbit: An orbit with approximately a 12-hour period. A circular Semi-Synchronous Orbit is at an altitude of approximately 20,200 km....
: An orbitOrbitIn physics, an orbit is the gravitationally curved path of an object around a point in space, for example the orbit of a planet around the center of a star system, such as the Solar System...
with an orbital periodOrbital periodThe orbital period is the time taken for a given object to make one complete orbit about another object.When mentioned without further qualification in astronomy this refers to the sidereal period of an astronomical object, which is calculated with respect to the stars.There are several kinds of...
equal to half of the average rotational period of the body being orbited and in the same direction of rotation as that body. For Earth this means a period of just under 12 hours at an altitudeAltitudeAltitude or height is defined based on the context in which it is used . As a general definition, altitude is a distance measurement, usually in the vertical or "up" direction, between a reference datum and a point or object. The reference datum also often varies according to the context...
of approximately 20,200 km (12,544.2 miles) if the orbit is circular.- Molniya orbitMolniya orbitMolniya orbit is a type of highly elliptical orbit with an inclination of 63.4 degrees, an argument of perigee of -90 degree and an orbital period of one half of a sidereal day...
: A semi-synchronous variation of a Tundra orbitTundra orbitTundra orbit is a type of highly elliptical geosynchronous orbit with a high inclination and an orbital period of one sidereal day . A satellite placed in this orbit spends most of its time over a chosen area of the Earth, a phenomenon known as apogee dwell...
. For Earth this means an orbital periodOrbital periodThe orbital period is the time taken for a given object to make one complete orbit about another object.When mentioned without further qualification in astronomy this refers to the sidereal period of an astronomical object, which is calculated with respect to the stars.There are several kinds of...
of just under 12 hours. Such a satellite spends most of its time over two designated areas of the planetPlanetA planet is a celestial body orbiting a star or stellar remnant that is massive enough to be rounded by its own gravity, is not massive enough to cause thermonuclear fusion, and has cleared its neighbouring region of planetesimals.The term planet is ancient, with ties to history, science,...
. An inclination of 63.4° is normally used to keep the perigee shift small.
- Molniya orbit
- Supersynchronous orbit: A disposal / storage orbit above GSO/GEO. Satellites will drift west. Also a synonymSynonymSynonyms are different words with almost identical or similar meanings. Words that are synonyms are said to be synonymous, and the state of being a synonym is called synonymy. The word comes from Ancient Greek syn and onoma . The words car and automobile are synonyms...
for Disposal orbit. - Subsynchronous orbitSubsynchronous orbitA subsynchronous orbit is an orbit of a satellite that is nearer the planet than it would be if it were in synchronous orbit, i.e. the orbital period is less than the sidereal day of the planet. An Earth satellite that is in subsynchronous orbit will appear to drift eastward as seen from the...
: A drift orbit close to but below GSO/GEO. Satellites will drift east. - Graveyard orbitGraveyard orbitA graveyard orbit, also called a supersynchronous orbit, junk orbit or disposal orbit, is an orbit significantly above synchronous orbit, where spacecraft are intentionally placed at the end of their operational life...
: An orbit a few hundred kilometers above geosynchronous that satellites are moved into at the end of their operation.- Disposal orbit: A synonymSynonymSynonyms are different words with almost identical or similar meanings. Words that are synonyms are said to be synonymous, and the state of being a synonym is called synonymy. The word comes from Ancient Greek syn and onoma . The words car and automobile are synonyms...
for graveyard orbitGraveyard orbitA graveyard orbit, also called a supersynchronous orbit, junk orbit or disposal orbit, is an orbit significantly above synchronous orbit, where spacecraft are intentionally placed at the end of their operational life...
. - Junk orbit: A synonymSynonymSynonyms are different words with almost identical or similar meanings. Words that are synonyms are said to be synonymous, and the state of being a synonym is called synonymy. The word comes from Ancient Greek syn and onoma . The words car and automobile are synonyms...
for graveyard orbitGraveyard orbitA graveyard orbit, also called a supersynchronous orbit, junk orbit or disposal orbit, is an orbit significantly above synchronous orbit, where spacecraft are intentionally placed at the end of their operational life...
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- Disposal orbit: A synonym
- Areosynchronous orbitAreosynchronous orbitAreosynchronous 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 synchronous orbitSynchronous orbitA synchronous orbit is an orbit in which an orbiting body has a period equal to the average rotational period of the body being orbited , and in the same direction of rotation as that body.-Properties:...
around the planet MarsMarsMars is the fourth planet from the Sun in the Solar System. The planet is named after the Roman god of war, Mars. It is often described as the "Red Planet", as the iron oxide prevalent on its surface gives it a reddish appearance...
with an orbital periodOrbital periodThe orbital period is the time taken for a given object to make one complete orbit about another object.When mentioned without further qualification in astronomy this refers to the sidereal period of an astronomical object, which is calculated with respect to the stars.There are several kinds of...
equal in length to Mars' sidereal day, 24.6229 hourHourThe hour is a unit of measurement of time. In modern usage, an hour comprises 60 minutes, or 3,600 seconds...
s. - Areostationary orbitAreostationary orbitAn areostationary orbit is a circular areosynchronous orbit in the Martian equatorial plane about above the surface, any point on which revolves about Mars in the same direction and with the same period as the Martian surface...
(ASO): A circularCircularCircular is a basic geometric shape such as a Circle.Circular may also refer to:-Documents:*Circular note, a document request by a bank to its foreign correspondents to pay a specified sum of money to a named person...
areosynchronous orbitAreosynchronous orbitAreosynchronous 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...
on the equatorial plane and about 17,000 kmKMKM, Km, or km may stand for:*Kilometre *Kernel methods*Kettle Moraine High School*Khmer language *Kuomintang , a centre-right political party in the Republic of China on Taiwan...
(10,557 mileMileA mile is a unit of length, most commonly 5,280 feet . The mile of 5,280 feet is sometimes called the statute mile or land mile to distinguish it from the nautical mile...
s) above the surface of Mars. To an observer on the ground this satellite would appear as a fixed point in the sky. - Heliosynchronous orbit: An heliocentric orbitHeliocentric orbitA heliocentric orbit is an orbit around the Sun. All planets, comets, and asteroids in our Solar System are in such orbits, as are many artificial probes and pieces of debris. The moons of planets in the Solar System, by contrast, are not in heliocentric orbits as they orbit their respective planet...
about the SunSunThe Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...
where the satellite's orbital periodOrbital periodThe orbital period is the time taken for a given object to make one complete orbit about another object.When mentioned without further qualification in astronomy this refers to the sidereal period of an astronomical object, which is calculated with respect to the stars.There are several kinds of...
matches the SunSunThe Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...
's period of rotationRotationA rotation is a circular movement of an object around a center of rotation. A three-dimensional object rotates always around an imaginary line called a rotation axis. If the axis is within the body, and passes through its center of mass the body is said to rotate upon itself, or spin. A rotation...
. These orbits occur at a radius of 24.360 GmGigametreA gigametre is a unit of length in the metric system, equal to one billion meters, the SI base unit of length, hence to 1,000,000 km or approximately 621,370 miles....
(0.1628 AUAstronomical unitAn astronomical unit is a unit of length equal to about or approximately the mean Earth–Sun distance....
) around the SunSunThe Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...
, a little less than half of the orbital radius of MercuryMercury (planet)Mercury is the innermost and smallest planet in the Solar System, orbiting the Sun once every 87.969 Earth days. The orbit of Mercury has the highest eccentricity of all the Solar System planets, and it has the smallest axial tilt. It completes three rotations about its axis for every two orbits...
.
Orbits in galaxies or galaxy models
- Box orbitBox orbitIn 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...
: An orbit in a triaxial elliptical galaxyElliptical galaxyAn elliptical galaxy is a galaxy having an approximately ellipsoidal shape and a smooth, nearly featureless brightness profile. They range in shape from nearly spherical to highly flat and in size from hundreds of millions to over one trillion stars...
that fills in a roughly box-shaped region. - Pyramid orbit: An orbit near a massive black holeSupermassive black holeA supermassive black hole is the largest type of black hole in a galaxy, in the order of hundreds of thousands to billions of solar masses. Most, and possibly all galaxies, including the Milky Way, are believed to contain supermassive black holes at their centers.Supermassive black holes have...
at the center of a triaxial galaxy. The orbit can be described as a Keplerian ellipse that precessesPrecessionPrecession is a change in the orientation of the rotation axis of a rotating body. It can be defined as a change in direction of the rotation axis in which the second Euler angle is constant...
about the black hole in two orthogonal directions, due to torqueTorqueTorque, moment or moment of force , is the tendency of a force to rotate an object about an axis, fulcrum, or pivot. Just as a force is a push or a pull, a torque can be thought of as a twist....
s from the triaxial galaxy.
Special classifications
- Sun-synchronous orbitSun-synchronous orbitA Sun-synchronous orbit is a geocentric orbit which combines altitude and inclination in such a way that an object on that orbit ascends or descends over any given point of the Earth's surface at the same local mean solar time. The surface illumination angle will be nearly the same every time...
: An orbit which combines altitudeAltitudeAltitude or height is defined based on the context in which it is used . As a general definition, altitude is a distance measurement, usually in the vertical or "up" direction, between a reference datum and a point or object. The reference datum also often varies according to the context...
and inclinationInclinationInclination in general is the angle between a reference plane and another plane or axis of direction.-Orbits:The inclination is one of the six orbital parameters describing the shape and orientation of a celestial orbit...
in such a way that the satellite passes over any given point of the planets's surface at the same local solar timeSolar timeSolar time is a reckoning of the passage of time based on the Sun's position in the sky. The fundamental unit of solar time is the day. Two types of solar time are apparent solar time and mean solar time .-Introduction:...
. Such an orbit can place a satellite in constant sunlight and is useful for imagingImagingImaging is the representation or reproduction of an object's outward form; especially a visual representation .- Imaging methodologies and technologies :...
, spySpy satelliteA spy satellite is an Earth observation satellite or communications satellite deployed for military or intelligence applications....
, and weather satelliteWeather satelliteThe weather satellite is a type of satellite that is primarily used to monitor the weather and climate of the Earth. Satellites can be either polar orbiting, seeing the same swath of the Earth every 12 hours, or geostationary, hovering over the same spot on Earth by orbiting over the equator while...
s. - Orbit of the Moon: The orbital characteristics of EarthEarthEarth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets...
's MoonMoonThe Moon is Earth's only known natural satellite,There are a number of near-Earth asteroids including 3753 Cruithne that are co-orbital with Earth: their orbits bring them close to Earth for periods of time but then alter in the long term . These are quasi-satellites and not true moons. For more...
. Average altitudeAltitudeAltitude or height is defined based on the context in which it is used . As a general definition, altitude is a distance measurement, usually in the vertical or "up" direction, between a reference datum and a point or object. The reference datum also often varies according to the context...
of 384,403 kilometres (238,857 mi), elliptical-inclined orbitInclined orbitA satellite is said to occupy an inclined orbit around the Earth if the orbit exhibits an angle other than zero degrees with the equatorial plane. This angle is called the orbit's inclination...
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Pseudo-orbit classifications
- Horseshoe orbitHorseshoe orbitA horseshoe orbit is a type of co-orbital motion of a small orbiting body relative to a larger orbiting body . The orbital period of the smaller body is very nearly the same as for the larger body, and its path appears to have a horseshoe shape in a rotating reference frame as viewed from the...
: An orbitOrbitIn physics, an orbit is the gravitationally curved path of an object around a point in space, for example the orbit of a planet around the center of a star system, such as the Solar System...
that appears to a ground observer to be orbiting a certain planetPlanetA planet is a celestial body orbiting a star or stellar remnant that is massive enough to be rounded by its own gravity, is not massive enough to cause thermonuclear fusion, and has cleared its neighbouring region of planetesimals.The term planet is ancient, with ties to history, science,...
but is actually in co-orbitCo-orbital configurationIn astronomy, a co-orbital configuration refers to two or more celestial objects that orbit at the same, or very similar, distance from their parent object as each other, i.e. they are in a 1:1 mean motion resonance....
with the planetPlanetA planet is a celestial body orbiting a star or stellar remnant that is massive enough to be rounded by its own gravity, is not massive enough to cause thermonuclear fusion, and has cleared its neighbouring region of planetesimals.The term planet is ancient, with ties to history, science,...
. See asteroids 3753 Cruithne3753 Cruithne3753 Cruithne is an asteroid in orbit around the Sun in approximate 1:1 orbital resonance with the Earth. It is a periodic inclusion planetoid orbiting the Sun in an apparent horseshoe orbit. It has been incorrectly called "Earth's second moon", but it is only a quasi-satellite. Cruithne never...
and 2002 AA292002 AA29' is a small near-Earth asteroid that was discovered on January 9, 2002 by the LINEAR automatic sky survey. The diameter of the asteroid is only about 50 to 110 metres . It revolves about the Sun on an almost circular orbit very similar to that of the Earth...
. - Exo-orbit: A maneuver where a spacecraftSpacecraftA spacecraft or spaceship is a craft or machine designed for spaceflight. Spacecraft are used for a variety of purposes, including communications, earth observation, meteorology, navigation, planetary exploration and transportation of humans and cargo....
achieves an orbitOrbitIn physics, an orbit is the gravitationally curved path of an object around a point in space, for example the orbit of a planet around the center of a star system, such as the Solar System...
that is unstable due to atmospheric drag. - Lunar transfer orbit (LTO)
- Prograde orbit: An orbitOrbitIn physics, an orbit is the gravitationally curved path of an object around a point in space, for example the orbit of a planet around the center of a star system, such as the Solar System...
with an inclination of less than 90°. Or rather, an orbit that is in the same direction as the rotation of the primary. - Retrograde orbit: An orbitOrbitIn physics, an orbit is the gravitationally curved path of an object around a point in space, for example the orbit of a planet around the center of a star system, such as the Solar System...
with an inclinationInclinationInclination in general is the angle between a reference plane and another plane or axis of direction.-Orbits:The inclination is one of the six orbital parameters describing the shape and orientation of a celestial orbit...
of more than 90°. Or rather, an orbit counter to the direction of rotation of the planet. Apart from those in Sun-synchronous orbitSun-synchronous orbitA Sun-synchronous orbit is a geocentric orbit which combines altitude and inclination in such a way that an object on that orbit ascends or descends over any given point of the Earth's surface at the same local mean solar time. The surface illumination angle will be nearly the same every time...
, few satellites are launched into retrograde orbit because the quantity of fuel required to launch them is much greater than for a prograde orbit. This is because when the rocket starts out on the ground, it already has an eastward component of velocityVelocityIn physics, velocity is speed in a given direction. Speed describes only how fast an object is moving, whereas velocity gives both the speed and direction of the object's motion. To have a constant velocity, an object must have a constant speed and motion in a constant direction. Constant ...
equal to the rotational velocity of the planet at its launch latitudeLatitudeIn geography, the latitude of a location on the Earth is the angular distance of that location south or north of the Equator. The latitude is an angle, and is usually measured in degrees . The equator has a latitude of 0°, the North pole has a latitude of 90° north , and the South pole has a...
. A gravity assist around the moon can reduce the fuel premium. Retrograde orbits might be used as part of anti-satellite warfareArtificial satellites in retrograde orbitArtificial satellites are rarely placed in retrograde orbit. This is partly due to the extra velocity required to go against the direction of the rotation of the Earth....
. - Halo orbitHalo orbitA halo orbit is a periodic, three-dimensional orbit near the , , or Lagrange points in the three-body problem of orbital mechanics. A spacecraft in a halo orbit does not technically orbit the Lagrange point itself , but travels in a closed, repeating path near the Lagrange point...
s and Lissajous orbitLissajous orbitIn orbital mechanics, a Lissajous orbit, , named after Jules Antoine Lissajous, is a quasi-periodic orbital trajectory that an object can follow around a Lagrangian point of a three-body system without requiring any propulsion. Lyapunov orbits around a libration point are curved paths that lie...
s: These are orbits around a Lagrangian pointLagrangian pointThe Lagrangian points are the five positions in an orbital configuration where a small object affected only by gravity can theoretically be stationary relative to two larger objects...
. Lagrange points are shown in the diagram on the right, and orbits near these points allow a spacecraft to stay in constant relative position with very little use of fuel. Orbits around the point are used by spacecraft that want a constant view of the Sun, such as the Solar and Heliospheric ObservatorySolar and Heliospheric ObservatoryThe Solar and Heliospheric Observatory is a spacecraft built by a European industrial consortium led by Matra Marconi Space that was launched on a Lockheed Martin Atlas IIAS launch vehicle on December 2, 1995 to study the Sun, and has discovered over 2100 comets. It began normal operations in May...
. Orbits around are used by missions that always want both the Earth and Sun behind them. This enables a single shield to block radiation from both the Earth and Sun, allowing passive cooling of sensitive instruments. Examples include the Wilkinson Microwave Anisotropy ProbeWilkinson Microwave Anisotropy ProbeThe Wilkinson Microwave Anisotropy Probe — also known as the Microwave Anisotropy Probe , and Explorer 80 — is a spacecraft which measures differences in the temperature of the Big Bang's remnant radiant heat — the Cosmic Microwave Background Radiation — across the full sky. Headed by Professor...
and the James Webb Space TelescopeJames Webb Space TelescopeThe James Webb Space Telescope , previously known as Next Generation Space Telescope , is a planned next-generation space telescope, optimized for observations in the infrared. The main technical features are a large and very cold 6.5 meter diameter mirror, an observing position far from Earth,...
. L1, L2, and L3 are unstable orbits, meaning that small perturbations will cause the orbiting craft to drift out of the orbit without periodic corrections.