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gamma-ray astronomy | Space and Astronomy | 1 | The subfield of astronomy that studies astronomical objects detectable at gamma-ray wavelengths. |
gamma-ray burst | Space and Astronomy | 1 | A cataclysmic event that generates a brief but intense outburst of gamma ray radiation which can be detected from billions of light-years away. The source of most GRBs is theorized to be supernova or hypernova explosions of high-mass stars. Short GRBs may also result from the collision of neutron stars. |
grb | Space and Astronomy | 1 | A cataclysmic event that generates a brief but intense outburst of gamma ray radiation which can be detected from billions of light-years away. The source of most GRBs is theorized to be supernova or hypernova explosions of high-mass stars. Short GRBs may also result from the collision of neutron stars. |
gas giant | Space and Astronomy | 1 | A giant planet composed mainly of hydrogen and helium gases rather than heavier elements, e.g. Jupiter and Saturn in the Solar System. |
geocenter | Space and Astronomy | 1 | The geometric center of the Earth, i.e. the arithmetic mean position of all points within the oblate spheroid that is the precise shape of the Earth. |
geocentric | Space and Astronomy | 1 | With reference to, or pertaining to, the geometric center of the Earth; centered upon the Earth, e.g. a geocentric orbit. |
geocentric zenith | Space and Astronomy | 1 | The point projected upon the celestial sphere by a straight line that passes through the geocenter and an observer; i.e. the observer's zenith as defined with respect to the center of the Earth. |
geometric albedo | Space and Astronomy | 1 | The ratio of the brightness of an astronomical body at a phase angle of zero to an idealized flat, fully reflecting, diffusively scattering (Lambertian) disk with the same cross-section. It is a measure of how much of the incoming illumination is being scattered back toward an observer and has a value between zero and one. |
geometric position | Space and Astronomy | 1 | The position of an object (celestial or otherwise) with respect to the center of the Earth or to the position of an observer, i.e. as defined by a straight line between the center of the Earth (or the observer) and the object at a given time, without any corrections for light-time, aberration, etc. |
geostationary orbit | Space and Astronomy | 1 | A circular geosynchronous orbit, which maintains a constant altitude of 35,786 kilometres (22,236 mi) directly above Earth's equator in the same direction as Earth's rotation such that, to an observer on Earth's surface, the orbiting object appears motionless, in a fixed position in the sky. Artificial satellites are often placed in geostationary orbit so that antennas on Earth do not have to rotate to track them. |
geosynchronous orbit | Space and Astronomy | 1 | A synchronous orbit about the Earth, i.e. with an orbital period equal to Earth's rotational period, such that the orbiting object appears to return to exactly the same position in the sky after a period of one sidereal day. All geosynchronous orbits have a semi-major axis equal to 35,786 kilometres (22,236 mi); geostationary orbits are a special case of geosynchronous orbits. |
gso | Space and Astronomy | 1 | A synchronous orbit about the Earth, i.e. with an orbital period equal to Earth's rotational period, such that the orbiting object appears to return to exactly the same position in the sky after a period of one sidereal day. All geosynchronous orbits have a semi-major axis equal to 35,786 kilometres (22,236 mi); geostationary orbits are a special case of geosynchronous orbits. |
giant planet | Space and Astronomy | 1 | Any very large or massive planet, including gas giants and ice giants. |
globular cluster | Space and Astronomy | 1 | A tight, spherical conglomeration of many thousands of stars which are gravitationally bound to each other and which orbit a galactic core as a satellite. They differ from open clusters in having a much higher combined mass, with a typical lifespan extending for billions of years. |
gravitational lens | Space and Astronomy | 1 | Any very large distribution of mass, such as a galactic cluster, which can bend passing light from a distant source by a noticeable degree. The effect, known as gravitational lensing, can make background objects appear to an observer to take on a ring or arc shape. |
gravitational-wave astronomy | Space and Astronomy | 1 | A branch of observational astronomy which analyzes minute distortions in the curvature of spacetime known as gravitational waves to collect observational data about astronomical objects and events such as neutron stars, black holes, supernovae, and the Big Bang. |
h ii region | Space and Astronomy | 1 | An ionized nebula powered by young, massive O-type stars. Ultraviolet photons from these hot stars ionize gas in the surrounding environment, and the nebular gas shines brightly in spectral lines of hydrogen and other elements. Because O-type stars have relatively short lifetimes (typically a few million years), the presence of an H II region indicates that massive star formation has taken place recently at that location. H II regions are often found in the arms of spiral galaxies and in star-forming irregular galaxies. |
heliocenter | Space and Astronomy | 1 | The precise geometric center of the Earth's Sun, i.e. the arithmetic mean position of all points within the approximate spheroid that is the shape of the Sun. |
heliocentric | Space and Astronomy | 1 | With reference to, or pertaining to, the geometric center of the Earth's Sun; centered upon the Sun, e.g. a heliocentric orbit. |
heliosphere | Space and Astronomy | 1 | The vast, bubble-like cavity in the interstellar medium which surrounds and is created by the plasma emanating from the Earth's Sun. The heliosphere encompasses the entirety of the Solar System and a vast region of space beyond it. Its outer limit is often considered the boundary between matter originating from the Sun and matter originating from the rest of the galaxy. |
hertzsprung–russell diagram | Space and Astronomy | 1 | A plot of luminosity versus effective temperature for a population of stars; depending on the usage, the star's absolute magnitude may be substituted for luminosity, and its color index or spectral type for temperature. Single stars of known mass and composition follow predictable tracks across this chart over the course of their evolution. Hence, knowing a star's mass and metallicity allows its age to be estimated. Stars of similar types are also found grouped together in specific regions of the chart, including main-sequence, red giant, and white dwarf stars. |
hill sphere | Space and Astronomy | 1 | The approximate region around an astronomical object within which its gravitational attraction dominates the motions of satellites. It is computed with respect to the next most gravitationally attractive object, such as the nearest star or the galactic core. Satellites moving outside this radius tend to be perturbed away from the main body. |
horizon | Space and Astronomy | 1 | The apparent boundary between the surface of a celestial body and its sky when viewed from the perspective of an observer on or near that body's surface; more specifically, the plane perpendicular to a line from an observer to the zenith that passes through the point of observation. |
hour angle | Space and Astronomy | 1 | For a given celestial object, the angular distance on the celestial sphere measured westward along the celestial equator from the observer's local meridian to the hour circle that passes through the celestial object; or, equivalently, the angle between the plane containing Earth's rotational axis and the zenith, and the plane containing Earth's rotational axis and the object of interest. Analogous to right ascension, the hour angle is one of many ways commonly used to specify the longitudinal position of an object upon the celestial sphere. |
hour circle | Space and Astronomy | 1 | Any imaginary great circle drawn upon the celestial sphere that passes through both of the celestial poles and is therefore perpendicular to the celestial equator. Similar to a meridian but additionally taking into account the terrain and the depth to the geocenter at a ground observer's particular location, the concept of the hour circle is employed to describe the longitudinal position of a celestial object relative to the observer's local meridian. |
hybrid pulsator | Space and Astronomy | 1 | This is a class of pulsating stars that display pulsation frequencies of two different classes of variables. An example are variables displaying characteristic frequencies of both Delta Scuti and Gamma Doradus variables. On the Hertzsprung–Russell diagram, these stars are positioned where the instability strips of both variable classes overlap. |
hydrogen burning limit | Space and Astronomy | 1 | A critical mass below which an astronomical object cannot sustain its surface luminosity through nuclear fusion. This mass limit, equal to about 7% of the mass of the Sun, forms the dividing line between brown dwarfs and hydrogen-fusing stars. |
hypergalaxy | Space and Astronomy | 1 | A system consisting of a large galaxy accompanied by multiple smaller satellite galaxies (often elliptical) as well as its galactic corona. The Milky Way and Andromeda systems are examples of hypergalaxies. |
ice giant | Space and Astronomy | 1 | A giant planet composed mainly of elements heavier than hydrogen or helium (such as oxygen, carbon, nitrogen, and sulfur), especially chemical volatiles with freezing points above 100 K (−173 °C), e.g. Uranus and Neptune in the Solar System. |
inclination | Space and Astronomy | 1 | See orbital inclination. |
inferior planet | Space and Astronomy | 1 | An archaic term that is sometimes used to refer to the planets Mercury and Venus. The name originated from the fact that these planets orbit closer to the Sun than the Earth and hence, in the geocentric cosmology of Ptolemy, both appear to travel with the Sun across the sky. This is in contrast to the so-called superior planets, such as Mars, which appear to move independently of the Sun. |
infrared astronomy | Space and Astronomy | 1 | The study of infrared radiation given out by gas and dust in space, particularly in the areas around forming stars. |
interstellar medium | Space and Astronomy | 1 | The matter that exists in the space between the stars in a galaxy. This medium mainly consists of hydrogen and helium, but is enhanced by traces of other elements contributed by matter expelled from stars. |
ism | Space and Astronomy | 1 | The matter that exists in the space between the stars in a galaxy. This medium mainly consists of hydrogen and helium, but is enhanced by traces of other elements contributed by matter expelled from stars. |
interstellar reddening | Space and Astronomy | 1 | An effect produced by the incremental absorption and scattering of electromagnetic energy from interstellar matter, known as extinction. This effect causes more distant objects such as stars to appear redder and dimmer than expected. It is not to be confused with the separate phenomenon of redshift. |
invariable plane | Space and Astronomy | 1 | The imaginary plane passing through the barycenter of a planetary system and perpendicular to its angular momentum vector, and which may be regarded as the weighted average of all planetary orbital and rotational planes comprising the system. |
irregular moon | Space and Astronomy | 1 | A natural satellite following a distant, inclined, and often eccentric and retrograde orbit about its primary. Irregular moons are thought to be captured from other orbits, as opposed to regular moons, which are thought to form in situ. |
isochrone | Space and Astronomy | 1 | A curve on the Hertzsprung–Russell diagram that represents the evolutionary positions of stars having the same age but differing masses. This is in contrast to an evolutionary track, which is a plot of stars having the same mass but differing ages. In fact, multiple evolutionary tracks can be used to build isochrones by putting curves through equal-age points along the tracks. When the mass of a star can be determined, an isochrone can be used to estimate the star's age. |
jeans instability | Space and Astronomy | 1 | A physical state in which an interstellar cloud of gas will begin to undergo collapse and form stars. A cloud can become unstable against collapse when it cools sufficiently or has perturbations of density, allowing gravity to overcome the gas pressure. |
julian year | Space and Astronomy | 1 | A unit of time defined as exactly 365.25 days of 86,400 SI seconds each. Because these are units of constant duration, the Julian year is also constant and does not vary with a specific calendar or with any of the other means of determining the length of a year, such as the tropical year. It is therefore widely used as the basis for defining the standard astronomical epoch and the light-year. |
a | Space and Astronomy | 1 | A unit of time defined as exactly 365.25 days of 86,400 SI seconds each. Because these are units of constant duration, the Julian year is also constant and does not vary with a specific calendar or with any of the other means of determining the length of a year, such as the tropical year. It is therefore widely used as the basis for defining the standard astronomical epoch and the light-year. |
kepler orbit | Space and Astronomy | 1 | The motion of one orbiting body relative to another, as an ellipse, parabola, or hyperbola, which forms a two-dimensional orbital plane (or sometimes a straight line) in three-dimensional space. Kepler orbits are idealized mathematical constructions which consider only the point-like gravitational attraction of two bodies, neglecting more complex orbital perturbations that may exist in reality. |
kuiper belt | Space and Astronomy | 1 | A circumstellar disc of small Solar System bodies such as asteroids, trojans, and centaurs in the outer Solar System, extending between 30 and 50 AU from the Sun. It is similar to the asteroid belt but far larger, and is home to several dwarf planets, including Pluto. |
libration | Space and Astronomy | 1 | A slight oscillating motion of the Moon as seen from the Earth, a result of the Moon's elliptical orbit. It can allow normally hidden parts of the Moon's far side to be visible along the limbs of the lunar disk. |
light-year | Space and Astronomy | 1 | A unit of length used to express astronomical distances that is equivalent to the distance that an object moving at the speed of light in vacuum would travel in one Julian year: approximately 9.46 trillion kilometres (9.46×1012 km) or 5.88 trillion miles (5.88×1012 mi). Though the light-year is often used to measure galactic-scale distances in non-specialist publications, the unit of length most commonly used in professional astrometry is the parsec. |
ly | Space and Astronomy | 1 | A unit of length used to express astronomical distances that is equivalent to the distance that an object moving at the speed of light in vacuum would travel in one Julian year: approximately 9.46 trillion kilometres (9.46×1012 km) or 5.88 trillion miles (5.88×1012 mi). Though the light-year is often used to measure galactic-scale distances in non-specialist publications, the unit of length most commonly used in professional astrometry is the parsec. |
limb darkening | Space and Astronomy | 1 | An optical effect seen in stars (including the Sun), where the center part of the disk appears brighter than the edge or limb of the image. |
line of apsides | Space and Astronomy | 1 | The imaginary line connecting the two apsides (the periapsis and the apoapsis) of an elliptical orbit, and which therefore represents the distance of the orbit's longest axis. |
lobster-eye optics | Space and Astronomy | 1 | An X-ray optics design with an ultra wide field of view, based on the structure of the eyes of a lobster. It allows X-ray light to enter from multiple angles, capturing more X-rays from a larger area than other X-ray telescopes. |
longitude of the ascending node | Space and Astronomy | 1 | The angle between a specified reference direction, called the origin of longitude, and the direction of an orbit's ascending node, as measured on a specified plane of reference. The angle is typically measured eastwards from the reference direction to the ascending node (i.e. counterclockwise as seen from the north). It is one of six canonical orbital elements used to characterize an orbit. |
luminosity | Space and Astronomy | 1 | The total amount of energy emitted per unit time by a star, galaxy, or other astronomical object. In SI units, luminosity is measured in joules per second or watts, and is often given in terms of astronomical magnitude. Luminosity is related to but distinct from visual brightness. |
lunar | Space and Astronomy | 1 | Of or relating to the Earth's Moon. |
lunar phase | Space and Astronomy | 1 | The shape of the portion of the Moon that is illuminated by direct sunlight as viewed from Earth. This shape is referred to as a phase because it gradually changes in a regular cycle over the course of a synodic month: as the orbital positions of the Moon around Earth and Earth around the Sun change, the visibility of the side of the Moon that constantly faces Earth alternates between completely illuminated (known as a full moon) and completely darkened by the Moon's own shadow (known as a new moon). There are also intermediate phases, during which the visible side may be only partially sunlit, e.g. when the Moon appears as a crescent. During the part of the lunar cycle in which the illuminated portion is growing larger, the Moon is said to be waxing; when the illuminated portion is becoming smaller, it is said to be waning. The phase of the Moon at any particular time appears the same from every point on Earth. |
massive compact halo object | Space and Astronomy | 1 | A kind of astronomical body that might explain the apparent presence of dark matter in galaxy halos. A MACHO is a body that emits little or no radiation and drifts through interstellar space unassociated with any planetary system. Examples of MACHOs include black holes or neutron stars as well as brown dwarfs and rogue planets. |
macho | Space and Astronomy | 1 | A kind of astronomical body that might explain the apparent presence of dark matter in galaxy halos. A MACHO is a body that emits little or no radiation and drifts through interstellar space unassociated with any planetary system. Examples of MACHOs include black holes or neutron stars as well as brown dwarfs and rogue planets. |
magnetic switchback | Space and Astronomy | 1 | A sudden reversals in the magnetic field of the solar wind. |
magnetosphere | Space and Astronomy | 1 | A mostly convex region formed when a plasma, such as the solar wind, interacts with the magnetic field of a body, such as a planet or star. |
magnitude | Space and Astronomy | 1 | A numerical logarithmic scale indicating the brightness of an astronomical object, where the lower the value, the brighter the object. By convention, a first magnitude star is 100 times as bright as a sixth magnitude star. Magnitude 6 is considered the lower limit of objects that can be seen with the naked eye, although this can vary depending on sky conditions and eyesight. |
main sequence | Space and Astronomy | 1 | A category of stars which form a continuous and distinctive band on plots of stellar temperature versus luminosity, in particular the Hertzsprung–Russell diagram. These stars are characterized by being in hydrostatic equilibrium and undergoing nuclear fusion of hydrogen-1 in their core region. The Sun is a main-sequence star. |
major axis | Space and Astronomy | 1 | See semi-major axis. |
march equinox | Space and Astronomy | 1 | The precise time of year on Earth when the Sun appears to cross the celestial equator, while generally trending northward at each zenith passage. It represents the moment at which the North Pole of the Earth begins to tilt toward the Sun, and typically occurs on or near March 20 each year. It is the vernal equinox in the Northern Hemisphere and the autumnal equinox in the Southern Hemisphere. Contrast September equinox. |
mean anomaly | Space and Astronomy | 1 | The fraction of an elliptical orbit's period that has elapsed since the orbiting body passed periapsis, expressed as the angular distance from the pericenter which a fictitious body would have if it moved in a perfectly circular orbit in the same orbital period as the actual body in its elliptical orbit. Unlike the true anomaly, the mean anomaly does not correspond to a real geometric angle but is instead a contrived parameter used to make calculating the position of the orbiting body in the two-body problem mathematically convenient. |
m | Space and Astronomy | 1 | The fraction of an elliptical orbit's period that has elapsed since the orbiting body passed periapsis, expressed as the angular distance from the pericenter which a fictitious body would have if it moved in a perfectly circular orbit in the same orbital period as the actual body in its elliptical orbit. Unlike the true anomaly, the mean anomaly does not correspond to a real geometric angle but is instead a contrived parameter used to make calculating the position of the orbiting body in the two-body problem mathematically convenient. |
mean-motion resonance | Space and Astronomy | 1 | See orbital resonance. |
mmr | Space and Astronomy | 1 | See orbital resonance. |
meridian | Space and Astronomy | 1 | A line running north–south across the sky and passing through the point directly overhead known as the zenith. |
meridian astronomy | Space and Astronomy | 1 | The measurement of positions of celestial objects based on observation of the times of their transit across the meridian and of their zenith distance at those times, with the intention of obtaining accurate star positions which are self-consistent over large areas of sky. |
messier object | Space and Astronomy | 1 | One of a set of 110 "nebulous" astronomical objects, 103 of which were catalogued as non-comets by French comet hunter Charles Messier between 1771 and 1781. The Messier catalogue includes most of the deep-sky objects easily visible from the Northern Hemisphere. |
meteor | Space and Astronomy | 1 | Shooting star. A meteor is the flash of light in the (usually night) sky when space debris or meteoroids burn up from friction with the Earth’s atmosphere. Note that ‘meteor’ refers to the flash of light, not the actual solid debris. |
meteorite | Space and Astronomy | 1 | A solid piece of debris from a meteor that originated in outer space and survived its passage through the atmosphere to reach the surface of a planet or moon. |
meteoroid | Space and Astronomy | 1 | Generally, astronomers reserve this term for chunks of space rocks less than 1.6 km in diameter (larger pieces are usually called asteroids). They are thought to be made from asteroid fragments following collision of these larger bodies. Most meteoroids that enter the Earth’s atmosphere vaporise completely because of the friction. |
meteor shower | Space and Astronomy | 1 | A series of meteors that seemingly radiate from a single area in the night sky. These are produced by debris left over from a larger body, such as a comet, and hence they follow roughly the same orbit. This makes many meteor showers predictable events, as they recur every year. |
metallicity | Space and Astronomy | 1 | A measure of the abundance of elements other than hydrogen and helium within an astronomical object. Note that this definition includes elements that are not traditionally considered metallic by chemical convention. |
micrometeorite | Space and Astronomy | 1 | A very small meteorite that has survived its passage through the atmosphere to reach the surface of a planet or moon, usually ranging in size from 50 μm to 2 mm. Micrometeorites are a major component of cosmic dust. |
micrometeoroid | Space and Astronomy | 1 | A very small meteoroid, usually weighing less than one gram. If it survives to reach a planetary surface, it is then termed a micrometeorite. |
microvariable | Space and Astronomy | 1 | A stellar object such as a variable star that undergoes very small variations in luminosity, in which the amplitude of the fluctuations amounts to just a few thousandths of a magnitude. Detecting microvariability typically requires a sufficient number of observations to rule out random error as a source. |
milky way | Space and Astronomy | 1 | The galaxy that contains our Solar System. |
minor axis | Space and Astronomy | 1 | See semi-minor axis. |
minor planet | Space and Astronomy | 1 | An object in direct orbit around the Sun that is neither a dominant planet nor originally classified as a comet. A moon is not a minor planet because it orbits another body instead of the Sun. |
minor-planet moon | Space and Astronomy | 1 | A natural satellite that orbits a minor planet. See also moonlet and subsatellite. |
molecular cloud | Space and Astronomy | 1 | An interstellar cloud in which the prevailing physical conditions allow molecules to form, including molecular hydrogen. |
moment of inertia factor | Space and Astronomy | 1 | A dimensionless quantity that characterizes the radial distribution of mass inside a planet or moon. |
moon | Space and Astronomy | 1 | See natural satellite. |
moon | Space and Astronomy | 1 | The solid, rocky body that orbits the Earth as its only natural satellite, completing a full orbit every 27.3 days. The Moon's gravitational influence is responsible for tides on Earth; because of tidal locking, only one side of the Moon is ever visible from the Earth. Sunlight reflected from its surface makes the Moon appear very bright in the night sky, though its orbital position with respect to the Earth and the Sun causes its visibility to change in a regular cycle of phases when viewed from the Earth. The adjectival lunar is often used specifically to describe the orbit, gravity, and other properties of the Earth's Moon. |
moonlet | Space and Astronomy | 1 | An especially small natural satellite orbiting a planet, dwarf planet, or other minor planet. See also minor-planet moon and subsatellite. |
moonmoon | Space and Astronomy | 1 | See subsatellite. |
morning width | Space and Astronomy | 1 | The horizontal angular distance between the rise azimuth of a celestial body and the east direction. |
moving group | Space and Astronomy | 1 | A loose grouping of stars which travel together through space. Although the members were formed together in the same molecular cloud, they have since moved too far apart to be gravitationally bound as a cluster. |
multi-messenger astronomy | Space and Astronomy | 1 | A type of astronomy based on the acquisition of information about astronomical objects through the coordinated observation and interpretation of four disparate classes of "messenger" signals with extrasolar origins: electromagnetic radiation, gravitational waves, neutrinos, and cosmic rays. Because these four extrasolar messengers are created by different astrophysical processes, their presence or absence during a celestial event can reveal useful information about their sources. |
n galaxy | Space and Astronomy | 1 | An early classification for active galaxies that had the visual appearance of a galaxy with a particularly bright, star-like nucleus. As a group, they are intermediate between Seyfert galaxies and Quasar. Most are giant ellipticals that are radio sources and display prominent emission lines. |
nadir | Space and Astronomy | 1 | The point on the celestial sphere exactly opposite from the zenith. Thus, where the zenith is directly above an observer, the nadir is underfoot. The zenith and nadir form the two poles of the horizon line. |
naked eye | Space and Astronomy | 1 | The human eye as used without any magnifying or light-collecting optical aid, such as a telescope, nor any eye protection. Many astronomical objects emit or reflect visible light that is sufficiently bright to fall within the limits of normal human visual perception, allowing observers to see them from the Earth's surface without any special equipment. Vision corrected to normal acuity using eyeglasses or contact lenses is still considered unaided. |
natural satellite | Space and Astronomy | 1 | Any astronomical body that orbits a planet, minor planet, or sometimes another small Solar System body. |
near-earth object | Space and Astronomy | 1 | Any small Solar System body, such as an asteroid or comet, whose orbit brings it into proximity with Earth, generally by being less than 1.3 AU from the Sun at its closest approach. |
neo | Space and Astronomy | 1 | Any small Solar System body, such as an asteroid or comet, whose orbit brings it into proximity with Earth, generally by being less than 1.3 AU from the Sun at its closest approach. |
nebula | Space and Astronomy | 1 | A cloud of dust or gas in space. Some nebulae are where stars are being born, others are thrown off by dying stars. |
neutrino | Space and Astronomy | 1 | A type of elementary particle, electrically neutral and with an extremely small rest mass, that interacts with other particles only via the weak interaction and the gravitational interaction. Neutrinos therefore typically pass through normal matter unimpeded and undetected. |
neutron star | Space and Astronomy | 1 | A type of compact star that is composed almost entirely of neutrons, which are a type of subatomic particle with no electrical charge. Typically, neutron stars have a mass between about 1.35 and 2.0 times the mass of the Sun, but with a radius of only 12 km (7.5 mi), making them among the densest known objects in the universe. |
night sky | Space and Astronomy | 1 | The appearance of the Earth's sky at nighttime, when the Sun is below the horizon, and more specifically when clear weather and low levels of ambient light permit visibility of celestial objects such as stars, planets, and the Moon. The night sky remains a fundamental setting for both amateur and professional observational astronomy. |
non-inclined orbit | Space and Astronomy | 1 | Any orbit that is coplanar with a specified plane of reference, such that the orbital inclination is 0 degrees for prograde orbits and 180 degrees for retrograde ones. |
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