In astronomy, what term describes the point in the orbit of a planet or comet at which it is farthest from the Sun?
"the comet could even have been ejected from the Solar System. This foreshadowed the modern scientific idea of chaos. Lexell's work on the orbit of the comet is considered to be the beginning of modern understanding of orbit determination. In a 2018 paper, ""Quan-Zhi Ye et al."" used recorded observations of the comet to recalculate the orbit, finding Le Verrier's 1844 calculations to be highly accurate. They simulated the orbit forwards to the year 2000, finding that 98% of possible orbits remained orbiting the Sun, 85% with a perihelion nearer than the asteroid belt, and 40% crossing Earth's orbit. The"
"Elongation (astronomy) In astronomy, a planet's elongation is the angular separation between the Sun and the planet, with Earth as the reference point. The greatest elongation of a given inferior planet occurs when this planet’s position, in its orbital path around the Sun, is at tangent to the observer on Earth. Since an inferior planet is well within the area of Earth's orbit around the Sun, observation of its elongation should not pose that much a challenge (compared to deep-sky objects, for example). When a planet is at its greatest elongation, it appears farthest from the Sun as viewed from"
"an ellipse. A circular orbit is a special case, wherein the foci of the ellipse coincide. The point where the orbiting body is closest to Earth is called the perigee, and is called the periapsis (less properly, ""perifocus"" or ""pericentron"") when the orbit is about a body other than Earth. The point where the satellite is farthest from Earth is called the apogee, apoapsis, or sometimes apifocus or apocentron. A line drawn from periapsis to apoapsis is the line-of-apsides. This is the major axis of the ellipse, the line through its longest part. Bodies following closed orbits repeat their paths"
"a moon of another planet from its central planet, for instance the angular distance of Io from Jupiter. Here we can also talk about ""greatest eastern elongation"" and ""greatest western elongation"". In the case of the moons of Uranus, one often talks about ""greatest northern elongation"" and ""greatest southern elongation"" instead, due to the very high inclination of Uranus' axis of rotation.. Elongation (astronomy) In astronomy, a planet's elongation is the angular separation between the Sun and the planet, with Earth as the reference point. The greatest elongation of a given inferior planet occurs when this planet’s position, in its"
"course of its year. A body's closest approach to the Sun is called its ""perihelion"", whereas its most distant point from the Sun is called its ""aphelion"". The orbits of the planets are nearly circular, but many comets, asteroids, and Kuiper belt objects follow highly elliptical orbits. The positions of the bodies in the Solar System can be predicted using numerical models. Although the Sun dominates the system by mass, it accounts for only about 2% of the angular momentum. The planets, dominated by Jupiter, account for most of the rest of the angular momentum due to the combination of"
"2018 VG18 , nicknamed ""Farout"", is a distant trans-Neptunian object. At an observed distance of ~ (more than three times the average distance of Pluto from the Sun, and nearly twice the average distance of Eris), as of December 2018 it is the most distant object in the Solar System ever observed (displacing the previous record holder, Eris, at 96 AU), and the first object discovered beyond , hence the nickname. However, it is not close to being the object with the most distant orbit on average, as its semi-major axis is only estimated to be about 95.2 AU (in"
"Proxima Centauri b Proxima Centauri b (also called Proxima b or Alpha Centauri Cb) is an exoplanet orbiting in the habitable zone of the red dwarf star Proxima Centauri, which is the closest star to the Sun and part of a triple star system. It is located about 4.2 light-years (1.3 parsecs, 40 trillion km, or 25 trillion miles) from Earth in the constellation of Centaurus, making it the closest known exoplanet to the Solar System. Proxima Centauri b orbits the star at a distance of roughly with an orbital period of approximately 11.2 Earth days, and has an estimated"
"Lunar orbit In astronomy, lunar orbit (also known as a selenocentric orbit) is 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. The altitude at apoapsis (point farthest from the surface) for a lunar orbit is known as apolune, apocynthion, or aposelene, while the periapsis (point closest to the surface) is known as perilune, pericynthion, or periselene, from names or epithets of the moon goddess. Low lunar orbit (LLO)—orbits below altitude—are"
"the orbit of the next nearer object to the Sun. For example, Venus is approximately 0.33 AU farther out from the Sun than Mercury, whereas Saturn is 4.3 AU out from Jupiter, and Neptune lies 10.5 AU out from Uranus. Attempts have been made to determine a relationship between these orbital distances (for example, the Titius–Bode law), but no such theory has been accepted. The images at the beginning of this section show the orbits of the various constituents of the Solar System on different scales. Some Solar System models attempt to convey the relative scales involved in the Solar"
"or within that planet. Owing to mutual gravitational perturbations, the eccentricities of the planetary orbits vary over time. Mercury, the smallest planet in the Solar System, has the most eccentric orbit. At the present epoch, Mars has the next largest eccentricity while the smallest orbital eccentricities are seen with Venus and Neptune. As two objects orbit each other, the periapsis is that point at which the two objects are closest to each other and the apoapsis is that point at which they are the farthest. (More specific terms are used for specific bodies. For example, ""perigee"" and ""apogee"" are the"
"terms ""inferior conjunction"" and ""superior conjunction"" are used in particular for the planets Mercury and Venus, which are inferior planets as seen from the Earth. However, this definition can be applied to any pair of planets, as seen from the one farther from the Sun. A planet (or asteroid or comet) is simply said to be in conjunction, when it is in conjunction with the Sun, as seen from the Earth. The Moon is in conjunction with the Sun at New Moon. In a quasiconjunction, a planet in retrograde motion — always either Mercury or Venus, from the point of"
"unmapped. There are also ongoing studies of the region between Mercury and the Sun. Objects may yet be discovered in the Solar System's uncharted regions. Currently, the furthest known objects, such as Comet West, have aphelia around 70,000 AU from the Sun, but as the Oort cloud becomes better known, this may change. The Solar System is located in the Milky Way, a barred spiral galaxy with a diameter of about 100,000 light-years containing about 100 billion stars. The Sun resides in one of the Milky Way's outer spiral arms, known as the Orion–Cygnus Arm or Local Spur. The Sun"
"noted the comet crossing over 42° of sky in 24 hours; he described the nucleus as being as large as Jupiter, ""surrounded with a coma of silver light, the brightest part of which was as large as the moon's orb"". Messier was the last astronomer to observe the comet as it moved away from the Sun, on October 3, 1770. Scientists at the time largely believed that comets originated outside the solar system, and therefore initial attempts to model the comet's orbit assumed a parabolic trajectory, which indicated a perihelion date (the date of the closest approach to the Sun)"
"Proxima Centauri Proxima Centauri (), or Alpha Centauri C, is a red dwarf, a small low-mass star, about from the Sun in the constellation of Centaurus. It was discovered in 1915 by Robert Innes and is the nearest-known star to the Sun. With a quiescent apparent magnitude of 11.13, it is too faint to be seen with the naked eye. Proxima Centauri forms a third component of the Alpha Centauri system, currently with a separation of about and an orbital period of 550,000 years. At present Proxima is 2.18° to the southwest of Alpha Centauri. Because of Proxima Centauri's proximity"
"orbit is at 30 AU). Its orbit has an eccentricity of 0.58 and an inclination of 8° with respect to the ecliptic. "" is among the most distant known Solar System objects. As of 2018, it is 63 AU from the Sun. It will make its closest approach to the Sun in 2093, when it will reach an apparent magnitude of 21.2. Additional precovery astrometry from the Sloan Digital Sky Survey and the Pan-STARRS1 survey shows that """" is a resonant trans-Neptunian object, securely trapped in a 2:9 mean motion resonance with Neptune, meaning that this minor planet orbits the"
"Declination In astronomy, declination (abbreviated dec; symbol δ) is one of the two angles that locate a point on the celestial sphere in the equatorial coordinate system, the other being hour angle. Declination's angle is measured north or south of the celestial equator, along the hour circle passing through the point in question. The root of the word ""declination"" (Latin, ""declinatio"") means ""a bending away"" or ""a bending down"". It comes from the same root as the words ""incline"" (""bend toward"") and ""recline"" (""bend backward""). In some 18th and 19th century astronomical texts, declination is given as ""North Pole Distance"""
"was calculated as 7.2 astronomical units (AU) from the Sun, placing it between Jupiter and Saturn and by far the greatest distance from Earth at which a comet had been discovered by amateurs. Most comets at this distance are extremely faint, and show no discernible activity, but Hale–Bopp already had an observable coma. An image taken at the Anglo-Australian Telescope in 1993 was found to show the then-unnoticed comet some 13 AU from the Sun, a distance at which most comets are essentially unobservable. (Halley's Comet was more than 100 times fainter at the same distance from the Sun.) Analysis"
"Distant minor planet A distant minor planet, or ""distant object"", is any minor planet found beyond Jupiter in the outer Solar System that is not commonly thought of as an ""asteroid"". The umbrella term is used by IAU's Minor Planet Center (MPC), which is responsible for the identification, designation and orbit computation of these objects. , the MPC maintains 3497 distant objects in its data base. Most distant minor planets are trans-Neptunian objects and centaurs, while relatively few are damocloids, Neptune trojans or Uranus trojans. All distant objects have a semi-major axis (average distance from the Sun) greater than 6"
"Kuiper belt The Kuiper belt (), occasionally called the Edgeworth–Kuiper belt, is a circumstellar disc in the outer Solar System, extending from the orbit of Neptune (at 30 AU) to approximately 50 AU from the Sun. It is similar to the asteroid belt, but is far larger—20 times as wide and 20 to 200 times as massive. Like the asteroid belt, it consists mainly of small bodies or remnants from when the Solar System formed. While many asteroids are composed primarily of rock and metal, most Kuiper belt objects are composed largely of frozen volatiles (termed ""ices""), such as methane,"
"Kepler-20f Kepler-20f (also known by its Kepler Object of Interest designation ""KOI-70.05"") is an exoplanet orbiting the Sun-like star Kepler-20, the second outermost of five such planets discovered by NASA's ""Kepler"" spacecraft. It is located approximately 929 light-years (285 parsecs, or about km) from Earth in the constellation Lyra. The exoplanet was found by using the transit method, in which the dimming effect that a planet causes as it crosses in front of its star is measured. The planet is notable as it has the closest radius to Earth known so far. Kepler-20f is very likely (>95% chance) a rocky"
"constellation Cassiopeia, similar to that of Achernar from Earth. Proxima Centauri Proxima Centauri (), or Alpha Centauri C, is a red dwarf, a small low-mass star, about from the Sun in the constellation of Centaurus. It was discovered in 1915 by Robert Innes and is the nearest-known star to the Sun. With a quiescent apparent magnitude of 11.13, it is too faint to be seen with the naked eye. Proxima Centauri forms a third component of the Alpha Centauri system, currently with a separation of about and an orbital period of 550,000 years. At present Proxima is 2.18° to the"
"Neptune Neptune is the eighth and farthest known planet from the Sun in the Solar System. In the Solar System, it is the fourth-largest planet by diameter, the third-most-massive planet, and the densest giant planet. Neptune is 17 times the mass of Earth and is slightly more massive than its near-twin Uranus, which is 15 times the mass of Earth and slightly larger than Neptune. Neptune orbits the Sun once every 164.8 years at an average distance of . It is named after the Roman god of the sea and has the astronomical symbol ♆, a stylised version of the"
"Heliocentric orbit A heliocentric orbit (also called circumsolar orbit) is an orbit around the barycenter of the Solar System, which is usually located within or very near the surface of the Sun. All planets, comets, and asteroids in the Solar System, and the Sun itself 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 (although the Moon has a convex orbit around the Sun). The barycenter of the Solar System, while always very near the"
"of Earth's orbital speed. When Sedna was discovered it was 89.6 AU from the Sun approaching perihelion, and was the most distant object in the Solar System observed. Eris was later detected by the same survey near aphelion at 97 AU. The orbits of some long-period comets extend farther than that of Sedna; they are too dim to be discovered except when approaching perihelion in the inner Solar System. Even as Sedna nears its perihelion in mid 2076, the Sun would appear merely as an extremely bright star-like pinpoint in its sky, 100 times brighter than a full moon on"
"but the specific details of the orbit have not yet been established, JPL's Small-Body Database currently lists the uncertainties of its orbit at greater than 100%. It may take several years of observation to properly characterize the orbit, due to the slow motion of the object. 2018 VG18 , nicknamed ""Farout"", is a distant trans-Neptunian object. At an observed distance of ~ (more than three times the average distance of Pluto from the Sun, and nearly twice the average distance of Eris), as of December 2018 it is the most distant object in the Solar System ever observed (displacing the"
"known as the heliosphere. The heliopause is the point at which pressure from the solar wind is equal to the opposing pressure of the interstellar medium; it extends out to the edge of the scattered disc. The Oort cloud, which is thought to be the source for long-period comets, may also exist at a distance roughly a thousand times further than the heliosphere. The Solar System is located in the Orion Arm, 26,000 light-years from the center of the Milky Way galaxy. For most of history, humanity did not recognize or understand the concept of the Solar System. Most people"
"Wisp or Light Sail type concepts). Such a system could grow organically if space-based solar power became a significant component of Earth's energy mix. Consumer demand for a multi-terawatt system would automatically create the necessary multi-million ton/year logistical system. Distances between the planets in the Solar System are often measured in astronomical units (AU), defined as the average distance between the Sun and Earth, some . Venus, the closest other planet to Earth is (at closest approach) 0.28 AU away. Neptune, the farthest planet from the Sun, is 29.8 AU away. As of January 2018, Voyager 1, the farthest man-made"
"Mercury (planet) Mercury is the smallest and innermost planet in the Solar System. Its orbital period around the Sun of 87.97 days is the shortest of all the planets in the Solar System. It is named after the Roman deity Mercury, the messenger of the gods. Like Venus, Mercury orbits the Sun within Earth's orbit as an ""inferior planet"", and never exceeds 28° away from the Sun. When viewed from Earth, this proximity to the Sun means the planet can only be seen near the western or eastern horizon during the early evening or early morning. At this time it"
"Quadrature (astronomy) In spherical astronomy, quadrature is the configuration of a celestial object in which its elongation is perpendicular to the direction of the Sun. It is applied especially to the position of a superior planet or the Moon at its first and last quarter phases. As shown in the diagram above, a planet (or other object) can be at the western quadrature (when it is to the west of the Sun when viewed from the Earth) or at the eastern quadrature (when it is to the east of the Sun when viewed from the Earth). Note that an inferior"
"approach to the Sun) is estimated to have occurred around September 2010. Aphelion (furthest distance from the Sun) is estimated to have occurred around February 2016. , the asteroid is estimated to be from Earth. Perihelion (closest approach to the Sun) may not occur again until August 2021. Orbits computed with only a handful of observations can be unreliable. Short observation arcs can result in computer generated orbits rejecting some data unnecessarily. The 2018 JPL orbit determination shows a semi-major axis of 4.9 AU (albeit with a large 20 AU uncertainty) which would be near Jupiter's orbit. Such an orbit"
"to as ""volatiles"". The distance from Earth to the Sun is . For comparison, the radius of the Sun is . Thus, the Sun occupies 0.00001% (10 %) of the volume of a sphere with a radius the size of Earth's orbit, whereas Earth's volume is roughly one millionth (10) that of the Sun. Jupiter, the largest planet, is from the Sun and has a radius of , whereas the most distant planet, Neptune, is from the Sun. With a few exceptions, the farther a planet or belt is from the Sun, the larger the distance between its orbit and"
"Orbiter Mission. Heliocentric orbit A heliocentric orbit (also called circumsolar orbit) is an orbit around the barycenter of the Solar System, which is usually located within or very near the surface of the Sun. All planets, comets, and asteroids in the Solar System, and the Sun itself 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 (although the Moon has a convex orbit around the Sun). The barycenter of the Solar System, while always very"
"in the outer Solar System. Located beyond the orbit of Neptune, "" is a non-resonant classical Kuiper belt object (cubewano) of the so-called hot population, which have higher inclinations than those of the cold population. It orbits the Sun at a distance of 40.4–48.5 AU once every 296 years and 2 months (108,178 days; semi-major axis of 44.43 AU). Its orbit has an eccentricity of 0.09 and an inclination of 7° with respect to the ecliptic. The body's observation arc begins at Kitt Peak with its first observation on 18 November 1998. As of 2018, this minor planet has not"