1.
90377 Sedna
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90377 Sedna is a large minor planet in the outer reaches of the Solar System that was, as of 2015, at a distance of about 86 astronomical units from the Sun, about three times as far as Neptune. Spectroscopy has revealed that Sednas surface composition is similar to that of some other objects, being largely a mixture of water, methane. Its surface is one of the reddest among Solar System objects and it is most likely a dwarf planet. Sedna has a long and elongated orbit, taking approximately 11,400 years to complete. These facts have led to speculation about its origin. The Minor Planet Center currently places Sedna in the scattered disc, others speculate that it might have been tugged into its current orbit by a passing star, perhaps one within the Suns birth cluster, or even that it was captured from another star system. Another hypothesis suggests that its orbit may be evidence for a planet beyond the orbit of Neptune. Astronomer Michael E. Sedna was discovered by Michael Brown, Chad Trujillo, the discovery formed part of a survey begun in 2001 with the Samuel Oschin telescope at Palomar Observatory near San Diego, California using Yales 160 megapixel Palomar Quest camera. On that day, an object was observed to move by 4.6 arcseconds over 3.1 hours relative to stars, later, the object was precovered on older images made by the Samuel Oschin telescope as well as on images from the Near-Earth Asteroid Tracking consortium. These previous positions expanded its known orbital arc and allowed a precise calculation of its orbit. The team made the name Sedna public before the object had been officially numbered, brian Marsden, the head of the Minor Planet Center, said that such an action was a violation of protocol, and that some members of the IAU might vote against it. However, no objection was raised to the name, and no competing names were suggested, Sedna has the longest orbital period of any known object in the Solar System of comparable size or larger, calculated at around 11,400 years. Its orbit is eccentric, with an aphelion estimated at 937 AU. This perihelion was the largest of that of any known Solar System object until the discovery of 2012 VP113, at its aphelion, Sedna orbits the Sun at a mere 4% of Earths orbital speed. When Sedna was discovered it was 89.6 AU from the Sun approaching perihelion, Eris was later detected by the same survey near aphelion at 97 AU. Only the orbits of some long-period comets extend farther than that of Sedna, when first discovered, Sedna was thought to have an unusually long rotational period. It was initially speculated that Sednas rotation was slowed by the pull of a large binary companion. Sedna has a V-band absolute magnitude of about 1.8, at the time of its discovery it was the intrinsically brightest object found in the Solar System since Pluto in 1930
2.
Trans-Neptunian object
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A trans-Neptunian object is any minor planet in the Solar System that orbits the Sun at a greater average distance than Neptune,30 astronomical units. Twelve minor planets with a semi-major axis greater than 150 AU and perihelion greater than 30 AU are known, the first trans-Neptunian object to be discovered was Pluto in 1930. It took until 1992 to discover a second trans-Neptunian object orbiting the Sun directly,1992 QB1, as of February 2017 over 2,300 trans-Neptunian objects appear on the Minor Planet Centers List of Transneptunian Objects. Of these TNOs,2,000 have a perihelion farther out than Neptune, as of November 2016,242 of these have their orbits well-enough determined that they have been given a permanent minor planet designation. The largest known object is Pluto, followed by Eris,2007 OR10, Makemake. The Kuiper belt, scattered disk, and Oort cloud are three divisions of this volume of space, though treatments vary and a few objects such as Sedna do not fit easily into any division. The orbit of each of the planets is slightly affected by the influences of the other planets. Discrepancies in the early 1900s between the observed and expected orbits of Uranus and Neptune suggested that there were one or more additional planets beyond Neptune, the search for these led to the discovery of Pluto in February 1930, which was too small to explain the discrepancies. Revised estimates of Neptunes mass from the Voyager 2 flyby in 1989 showed that the problem was spurious, Pluto was easiest to find because it has the highest apparent magnitude of all known trans-Neptunian objects. It also has an inclination to the ecliptic than most other large TNOs. After Plutos discovery, American astronomer Clyde Tombaugh continued searching for years for similar objects. For a long time, no one searched for other TNOs as it was believed that Pluto. Only after the 1992 discovery of a second TNO,1992 QB1, a broad strip of the sky around the ecliptic was photographed and digitally evaluated for slowly moving objects. Hundreds of TNOs were found, with diameters in the range of 50 to 2,500 kilometers, Pluto and Eris were eventually classified as dwarf planets by the International Astronomical Union. Kuiper belt objects are classified into the following two groups, Resonant objects are locked in an orbital resonance with Neptune. Objects with a 1,2 resonance are called twotinos, and objects with a 2,3 resonance are called plutinos, after their most prominent member, classical Kuiper belt objects have no such resonance, moving on almost circular orbits, unperturbed by Neptune. Examples are 1992 QB1,50000 Quaoar and Makemake, the scattered disc contains objects farther from the Sun, usually with very irregular orbits. A typical example is the most massive known TNO, Eris, scattered-extended —Scattered-extended objects have a Tisserand parameter greater than 3 and have a time-averaged eccentricity greater than 0
3.
Perihelion and aphelion
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The perihelion is the point in the orbit of a celestial body where it is nearest to its orbital focus, generally a star. It is the opposite of aphelion, which is the point in the orbit where the body is farthest from its focus. The word perihelion stems from the Ancient Greek words peri, meaning around or surrounding, aphelion derives from the preposition apo, meaning away, off, apart. According to Keplers first law of motion, all planets, comets. Hence, a body has a closest and a farthest point from its parent object, that is, a perihelion. Each extreme is known as an apsis, orbital eccentricity measures the flatness of the orbit. Because of the distance at aphelion, only 93. 55% of the solar radiation from the Sun falls on a given area of land as does at perihelion. However, this fluctuation does not account for the seasons, as it is summer in the northern hemisphere when it is winter in the southern hemisphere and vice versa. Instead, seasons result from the tilt of Earths axis, which is 23.4 degrees away from perpendicular to the plane of Earths orbit around the sun. Winter falls on the hemisphere where sunlight strikes least directly, and summer falls where sunlight strikes most directly, in the northern hemisphere, summer occurs at the same time as aphelion. Despite this, there are larger land masses in the northern hemisphere, consequently, summers are 2.3 °C warmer in the northern hemisphere than in the southern hemisphere under similar conditions. Apsis Ellipse Solstice Dates and times of Earths perihelion and aphelion, 2000–2025 from the United States Naval Observatory
4.
Astronomical unit
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The astronomical unit is a unit of length, roughly the distance from Earth to the Sun. However, that varies as Earth orbits the Sun, from a maximum to a minimum. Originally conceived as the average of Earths aphelion and perihelion, it is now defined as exactly 149597870700 metres, the astronomical unit is used primarily as a convenient yardstick for measuring distances within the Solar System or around other stars. However, it is also a component in the definition of another unit of astronomical length. A variety of symbols and abbreviations have been in use for the astronomical unit. In a 1976 resolution, the International Astronomical Union used the symbol A for the astronomical unit, in 2006, the International Bureau of Weights and Measures recommended ua as the symbol for the unit. In 2012, the IAU, noting that various symbols are presently in use for the astronomical unit, in the 2014 revision of the SI Brochure, the BIPM used the unit symbol au. In ISO 80000-3, the symbol of the unit is ua. Earths orbit around the Sun is an ellipse, the semi-major axis of this ellipse is defined to be half of the straight line segment that joins the aphelion and perihelion. The centre of the sun lies on this line segment. In addition, it mapped out exactly the largest straight-line distance that Earth traverses over the course of a year, knowing Earths shift and a stars shift enabled the stars distance to be calculated. But all measurements are subject to some degree of error or uncertainty, improvements in precision have always been a key to improving astronomical understanding. Improving measurements were continually checked and cross-checked by means of our understanding of the laws of celestial mechanics, the expected positions and distances of objects at an established time are calculated from these laws, and assembled into a collection of data called an ephemeris. NASAs Jet Propulsion Laboratory provides one of several ephemeris computation services, in 1976, in order to establish a yet more precise measure for the astronomical unit, the IAU formally adopted a new definition. Equivalently, by definition, one AU is the radius of an unperturbed circular Newtonian orbit about the sun of a particle having infinitesimal mass. As with all measurements, these rely on measuring the time taken for photons to be reflected from an object. However, for precision the calculations require adjustment for such as the motions of the probe. In addition, the measurement of the time itself must be translated to a scale that accounts for relativistic time dilation
5.
Semi-major and semi-minor axes
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In geometry, the major axis of an ellipse is its longest diameter, a line segment that runs through the center and both foci, with ends at the widest points of the perimeter. The semi-major axis is one half of the axis, and thus runs from the centre, through a focus. Essentially, it is the radius of an orbit at the two most distant points. For the special case of a circle, the axis is the radius. One can think of the axis as an ellipses long radius. The semi-major axis of a hyperbola is, depending on the convention, thus it is the distance from the center to either vertex of the hyperbola. A parabola can be obtained as the limit of a sequence of ellipses where one focus is fixed as the other is allowed to move arbitrarily far away in one direction. Thus a and b tend to infinity, a faster than b, the semi-minor axis is a line segment associated with most conic sections that is at right angles with the semi-major axis and has one end at the center of the conic section. It is one of the axes of symmetry for the curve, in an ellipse, the one, in a hyperbola. The semi-major axis is the value of the maximum and minimum distances r max and r min of the ellipse from a focus — that is. In astronomy these extreme points are called apsis, the semi-minor axis of an ellipse is the geometric mean of these distances, b = r max r min. The eccentricity of an ellipse is defined as e =1 − b 2 a 2 so r min = a, r max = a. Now consider the equation in polar coordinates, with one focus at the origin, the mean value of r = ℓ / and r = ℓ /, for θ = π and θ =0 is a = ℓ1 − e 2. In an ellipse, the axis is the geometric mean of the distance from the center to either focus. The semi-minor axis of an ellipse runs from the center of the ellipse to the edge of the ellipse, the semi-minor axis is half of the minor axis. The minor axis is the longest line segment perpendicular to the axis that connects two points on the ellipses edge. The semi-minor axis b is related to the axis a through the eccentricity e. A parabola can be obtained as the limit of a sequence of ellipses where one focus is fixed as the other is allowed to move arbitrarily far away in one direction
6.
2012 VP113
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2012 VP113 is a planetoid in the outer reaches of the Solar System. It is the object with the farthest known perihelion in the Solar System and its discovery was announced on 26 March 2014. It has a magnitude of 4.0, which makes it likely to be a dwarf planet. It is expected to be half the size of Sedna. Its surface is thought to have a pink tinge, resulting from chemical changes produced by the effect of radiation on frozen water, methane and this optical color is consistent with formation in the gas-giant region and not the classical Kuiper belt, which is dominated by ultra-red colored objects. 2012 VP113 was first observed on 5 November 2012 with NOAOs 4-meter Víctor M. Blanco Telescope at the Cerro Tololo Inter-American Observatory, carnegie’s 6. 5-meter Magellan telescope at Las Campanas Observatory in Chile was used to determine its orbit and surface properties. Before being announced to the public, it was tracked by Cerro Tololo Inter-American Observatory. It has an arc of about 2 years. Two precovery measurements from 22 October 2011 have been reported, a primary issue with observing it and finding precovery observations of it is that at an apparent magnitude of 23, it is too faint for most telescopes to easily observe. 2012 VP113 was abbreviated VP and nicknamed Biden by the team, after Joe Biden. 2012 VP113 has the largest perihelion distance of any object in the Solar System. Its last perihelion was around 1979, at a distance of 80 AU, it is currently 83 AU from the Sun. Only eight other Solar System objects are known to have larger than 47 AU. The paucity of bodies with perihelia at 50–75 AU appears not to be an observational artifact and it is possibly a member of a hypothesized Hills cloud. It has a perihelion, argument of perihelion, and current position in the sky similar to those of Sedna, in fact, all known Solar System bodies with semi-major axes over 150 AU and perihelia greater than Neptunes have arguments of perihelion clustered near 340 ± 55°. This could indicate a similar mechanism for these bodies. 2000 CR105 was the first such object discovered and it is currently unknown how 2012 VP113 acquired a perihelion distance beyond the Kuiper belt. The orbital architecture of the region may signal the presence of more than one planet
7.
Solar System
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The Solar System is the gravitationally bound system comprising the Sun and the objects that orbit it, either directly or indirectly. Of those objects that orbit the Sun directly, the largest eight are the planets, with the remainder being significantly smaller objects, such as dwarf planets, of the objects that orbit the Sun indirectly, the moons, two are larger than the smallest planet, Mercury. The Solar System formed 4.6 billion years ago from the collapse of a giant interstellar molecular cloud. The vast majority of the mass is in the Sun. The four smaller inner planets, Mercury, Venus, Earth and Mars, are terrestrial planets, being composed of rock. The four outer planets are giant planets, being more massive than the terrestrials. All planets have almost circular orbits that lie within a flat disc called the ecliptic. The Solar System also contains smaller objects, the asteroid belt, which lies between the orbits of Mars and Jupiter, mostly contains objects composed, like the terrestrial planets, of rock and metal. Beyond Neptunes orbit lie the Kuiper belt and scattered disc, which are populations of trans-Neptunian objects composed mostly of ices, within these populations are several dozen to possibly tens of thousands of objects large enough that they have been rounded by their own gravity. Such objects are categorized as dwarf planets, identified dwarf planets include the asteroid Ceres and the trans-Neptunian objects Pluto and Eris. In addition to two regions, various other small-body populations, including comets, centaurs and interplanetary dust clouds. Six of the planets, at least four of the dwarf planets, each of the outer planets is encircled by planetary rings of dust and other small objects. The solar wind, a stream of charged particles flowing outwards from the Sun, 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, the Solar System is located in the Orion Arm,26,000 light-years from the center of the Milky Way. For most of history, humanity did not recognize or understand the concept of the Solar System, the invention of the telescope led to the discovery of further planets and moons. The principal component of the Solar System is the Sun, a G2 main-sequence star that contains 99. 86% of the known mass. The Suns four largest orbiting bodies, the giant planets, account for 99% of the mass, with Jupiter. The remaining objects of the Solar System together comprise less than 0. 002% of the Solar Systems total mass, most large objects in orbit around the Sun lie near the plane of Earths orbit, known as the ecliptic
8.
Detached object
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Detached objects are a dynamical class of minor planets in the outer reaches of the Solar System and belong to the broader family of trans-Neptunian objects. This reflects the dynamical gradation that can exist between the parameters of the scattered disk and the detached population. At least nine such bodies have been identified, of which the largest, most distant. Those with perihelia greater than 75 AU are termed sednoids, as of 2016, there are two known sednoids, Sedna and 2012 VP113. Detached objects have much larger than Neptunes aphelion. They often have highly elliptical, very large orbits with semi-major axes of up to a few hundred astronomical units, such orbits cannot have been created by gravitational scattering by the giant planets. Instead, a number of explanations have been put forward, including an encounter with a star or a distant planet-sized object. The classification suggested by the Deep Ecliptic Survey team introduces a distinction between scattered-near objects and scattered-extended objects using a Tisserands parameter value of 3. Detached objects are one of five distinct classes of TNO, the other four classes are classical Kuiper-belt objects, resonant objects, scattered-disc objects. Detached objects generally have a distance greater than 40 AU, deterring strong interactions with Neptune. However, there are no boundaries between the scattered and detached regions, since both can coexist as TNOs in an intermediate region with perihelion distance between 37 and 40 AU. One such intermediate body with a well determined orbit is 2003 FY128, although Sedna is officially considered a scattered-disc object by the MPC, its discoverer Michael E. This classification of Sedna as an object is accepted in recent publications. They have orbital periods of more than 300 years and most have only observed over a short observation arc of a couple years. Further improvement in the orbit and potential resonance of objects will help to understand the migration of the giant planets. For example, simulations by Emel’yanenko and Kiseleva in 2007 show that many distant objects could be in resonance with Neptune. They show a 10% likelihood that 2000 CR105 is in a 20,1 resonance, a 38% likelihood that 2003 QK91 is in a 10,3 resonance, and an 84% likelihood that 2000 YW134 is in an 8,3 resonance. The likely dwarf planet 2005 TB190 appears to have less than a 1% likelihood of being in a 4,1 resonance
9.
Oort cloud
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The Oort cloud, sometimes called the Öpik–Oort cloud, is a theoretical cloud of predominantly icy planetesimals believed to surround the Sun to as far as somewhere between 50,000 and 200,000 AU. It is divided into two regions, a disc-shaped inner Oort cloud and a spherical outer Oort cloud, both regions lie beyond the heliosphere and in interstellar space. The Kuiper belt and the disc, the other two reservoirs of trans-Neptunian objects, are less than one thousandth as far from the Sun as the Oort cloud. The outer limit of the Oort cloud defines the boundary of the Solar System. The outer Oort cloud is only bound to the Solar System. These forces occasionally dislodge comets from their orbits within the cloud, based on their orbits, most of the short-period comets may come from the scattered disc, but some may still have originated from the Oort cloud. In 1932, the Estonian astronomer Ernst Öpik postulated that long-period comets originated in a cloud at the outermost edge of the Solar System. The idea was revived by Dutch astronomer Jan Oort as a means to resolve a paradox. Thus, Oort reasoned, a comet could not have formed while in its current orbit, there are two main classes of comet, short-period comets and long-period comets. Ecliptic comets have relatively small orbits, below 10 AU, and follow the ecliptic plane, all long-period comets have very large orbits, on the order of thousands of AU, and appear from every direction in the sky. Oort noted that there was a peak in numbers of comets with aphelia of roughly 20,000 AU. The Oort cloud is thought to occupy a vast space from somewhere between 2,000 and 5,000 AU to as far as 50,000 AU from the Sun, some estimates place the outer edge at between 100,000 and 200,000 AU. The region can be subdivided into a spherical outer Oort cloud of 20, 000–50,000 AU, the outer cloud is only weakly bound to the Sun and supplies the long-period comets to inside the orbit of Neptune. The inner Oort cloud is known as the Hills cloud, named after Jack G. Hills. The Hills cloud explains the existence of the Oort cloud after billions of years. The outer Oort cloud may have trillions of objects larger than 1 km, earlier it was thought to be more massive, but improved knowledge of the size distribution of long-period comets led to lower estimates. The mass of the inner Oort cloud has not been characterized, if analyses of comets are representative of the whole, the vast majority of Oort-cloud objects consist of ices such as water, methane, ethane, carbon monoxide and hydrogen cyanide. The Oort cloud is thought to be a remnant of the protoplanetary disc that formed around the Sun approximately 4.6 billion years ago
10.
Perturbation (astronomy)
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In astronomy, perturbation is the complex motion of a massive body subject to forces other than the gravitational attraction of a single other massive body. The other forces can include a body, resistance, as from an atmosphere. The study of perturbations began with the first attempts to predict planetary motions in the sky, in ancient times the causes were a mystery. Newton, at the time he formulated his laws of motion and of gravitation, applied them to the first analysis of perturbations, the complex motions of gravitational perturbations can be broken down. The hypothetical motion that the body follows under the effect of one other body only is typically a conic section. This is called a problem, or an unperturbed Keplerian orbit. The differences between that and the motion of the body are perturbations due to the additional gravitational effects of the remaining body or bodies. If there is one other significant body then the perturbed motion is a three-body problem. A general analytical solution exists for the problem, when more than two bodies are considered analytic solutions exist only for special cases. Even the two-body problem becomes insoluble if one of the bodies is irregular in shape, most systems that involve multiple gravitational attractions present one primary body which is dominant in its effects. The gravitational effects of the bodies can be treated as perturbations of the hypothetical unperturbed motion of the planet or satellite around its primary body. In methods of general perturbations, general differential equations, either of motion or of change in the elements, are solved analytically, usually by series expansions. The result is expressed in terms of algebraic and trigonometric functions of the orbital elements of the body in question. This can be applied generally to many different sets of conditions, historically, general perturbations were investigated first. The classical methods are known as variation of the elements, variation of parameters or variation of the constants of integration, in these methods, it is considered that the body is always moving in a conic section, however the conic section is constantly changing due to the perturbations. General perturbations is applicable if the perturbing forces are about one order of magnitude smaller, or less. In the Solar System, this is usually the case, Jupiter, general perturbation methods are preferred for some types of problems, as the source of certain observed motions are readily found. In effect, the positions and velocities are perturbed directly, special perturbations can be applied to any problem in celestial mechanics, as it is not limited to cases where the perturbing forces are small
11.
Giant planet
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A giant planet is any massive planet. They are usually composed of low-boiling-point materials, rather than rock or other solid matter. There are four giant planets in the Solar System, Jupiter, Saturn, Uranus. Many extrasolar giant planets have been identified orbiting other stars, giant planets are also sometimes called jovian planets, after Jupiter. They are also known as gas giants. However, many astronomers apply the term only to Jupiter and Saturn, classifying Uranus and Neptune. Both names are misleading, all of the giant planets consist primarily of fluids above their critical points. The principal components are hydrogen and helium in the case of Jupiter and Saturn, the defining differences between a very low-mass brown dwarf and a gas giant are debated. One school of thought is based on formation, the other, part of the debate concerns whether brown dwarfs must, by definition, have experienced nuclear fusion at some point in their history. The term gas giant was coined in 1952 by the fiction writer James Blish and was originally used to refer to all giant planets. Arguably it is something of a misnomer, because throughout most of the volume of these planets the pressure is so high that matter is not in gaseous form. Other than solids in the core and the layers of the atmosphere, all matter is above the critical point. Fluid planet would be an accurate term. Jupiter also has metallic hydrogen near its center, but much of its volume is hydrogen, helium, the observable atmospheres of all these planets are quite thin compared to their radii, only extending perhaps one percent of the way to the center. Thus the observable portions are gaseous, in the outer Solar System, hydrogen and helium are referred to as gases, water, methane, and ammonia as ices, and silicates and metals as rock. When deep planetary interiors are considered, it may not be far off to say that, by ice astronomers mean oxygen and carbon, by rock they mean silicon, and by gas they mean hydrogen and helium. The many ways in which Uranus and Neptune differ from Jupiter, with this terminology in mind, some astronomers have started referring to Uranus and Neptune as ice giants to indicate the predominance of the ices in their interior composition. The alternative term jovian planet refers to the Roman god Jupiter—the genitive form of which is Jovis, objects large enough to start deuterium fusion are called brown dwarfs, and these occupy the mass range between that of large giant planets and the lowest-mass stars
12.
Galactic tide
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A galactic tide is tidal force experienced by objects subject to the gravitational field of a galaxy such as the Milky Way. Tidal forces are dependent on the gradient of a field, rather than its strength. Two interacting galaxies will not always collide head-on, and the tidal forces will distort each galaxy along an axis pointing roughly towards, such tails are typically strongly curved. If a tail appears to be straight, it is probably being viewed edge-on, the stars and gas that comprise the tails will have been pulled from the easily distorted galactic discs of one or both bodies, rather than the gravitationally bound galactic centres. Two very prominent examples of collisions producing tidal tails are the Mice Galaxies, just as the Moon raises two water tides on opposite sides of the Earth, so a galactic tide produces two arms in its galactic companion. Secondly, if one of the two galaxies is in the foreground, then the second galaxy — and the bridge between them — may be partially obscured, together, these effects can make it hard to see where one galaxy ends and the next begins. Tidal loops, where a tail joins with its parent galaxy at both ends, are rarer still, because tidal effects are strongest in the immediate vicinity of a galaxy, satellite galaxies are particularly likely to be affected. The stripping mechanism is the same as between two galaxies, although its comparatively weak gravitational field ensures that only the satellite, not the host galaxy, is affected. If the satellite is very small compared to the host, the tidal tails produced are likely to be symmetric. It has been suggested that the discs of gas and stars around some galaxies, such as Andromeda. Tidal effects are present within a galaxy, where their gradients are likely to be steepest. This can have consequences for the formation of stars and planetary systems, typically a stars gravity will dominate within its own system, with only the passage of other stars substantially affecting dynamics. However, at the outer reaches of the system, the gravity is weak. In the Solar System, the hypothetical Oort cloud, believed to be the source of long-period comets, the Oort cloud is believed to be a vast shell surrounding the Solar System, possibly over a light-year in radius. Across such a vast distance, the gradient of the Milky Ways gravitational field plays a far more noticeable role, such a body, being composed of a rock and ice mixture, would become a comet when subjected to the increased solar radiation present in the inner Solar System. It has been suggested that the tide may also contribute to the formation of an Oort cloud. This shows that the effects of the tide are quite complex. Cumulatively the effect can be significant, however, up to 90% of all comets originating from an Oort cloud may be the result of the galactic tide
13.
Accretion (astrophysics)
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In astrophysics, accretion is the accumulation of particles into a massive object by gravitationally attracting more matter, typically gaseous matter, in an accretion disk. Most astronomical objects, such as galaxies, stars, and planets, are formed by accretion processes, the idea proposed in the 19th century that Earth and the other terrestrial planets formed from meteoric material was developed in a quantitative way in 1969 by Viktor Safronov. He calculated, in detail, the different stages of planet formation. Since then, the theory has been developed using intensive numerical simulations to study planetesimal accumulation. Stars form by the collapse of interstellar gas. Prior to collapse, this gas is mostly in the form of molecular clouds, as the cloud collapses, losing potential energy, it heats up, gaining kinetic energy, and the conservation of angular momentum ensures that the cloud forms a flatted disk—the accretion disk. A few hundred years after the Big Bang, the Universe cooled to the point where atoms could form. As the Universe continued to expand and cool, the atoms lost enough kinetic energy, as further accretion occurred, galaxies formed. Galaxies grow through mergers and smooth gas accretion, accretion also occurs inside galaxies, forming stars. Stars are thought to form inside giant clouds of cold molecular hydrogen—giant molecular clouds of roughly 300,000 M☉ and 65 light-years in diameter, over millions of years, giant molecular clouds are prone to collapse and fragmentation. These fragments then form small, dense cores, which in turn collapse into stars, the cores range in mass from a fraction to several times that of the Sun and are called protostellar nebulae. They possess diameters of 2, 000–20,000 astronomical units, compare it with the particle number density of the air at the sea level—2. 8×1019/cm3. The initial collapse of a solar-mass protostellar nebula takes around 100,000 years, every nebula begins with a certain amount of angular momentum. This core forms the seed of what will become a star, as the collapse continues, conservation of angular momentum dictates that the rotation of the infalling envelope accelerates, which eventually forms a disk. Around this time the protostar begins to fuse deuterium, if the protostar is sufficiently massive, hydrogen fusion follows. Otherwise, if its mass is too low, the object becomes a brown dwarf and this birth of a new star occurs approximately 100,000 years after the collapse begins. Objects at this stage are known as Class I protostars, which are also called young T Tauri stars, evolved protostars, or young stellar objects. By this time, the star has already accreted much of its mass
14.
Apsis
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An apsis is an extreme point in an objects orbit. The word comes via Latin from Greek and is cognate with apse, for elliptic orbits about a larger body, there are two apsides, named with the prefixes peri- and ap-, or apo- added to a reference to the thing being orbited. For a body orbiting the Sun, the point of least distance is the perihelion, the terms become periastron and apastron when discussing orbits around other stars. For any satellite of Earth including the Moon the point of least distance is the perigee, for objects in Lunar orbit, the point of least distance is the pericynthion and the greatest distance the apocynthion. For any orbits around a center of mass, there are the terms pericenter and apocenter, periapsis and apoapsis are equivalent alternatives. A straight line connecting the pericenter and apocenter is the line of apsides and this is the major axis of the ellipse, its greatest diameter. For a two-body system the center of mass of the lies on this line at one of the two foci of the ellipse. When one body is larger than the other it may be taken to be at this focus. Historically, in systems, apsides were measured from the center of the Earth. In orbital mechanics, the apsis technically refers to the distance measured between the centers of mass of the central and orbiting body. However, in the case of spacecraft, the family of terms are used to refer to the orbital altitude of the spacecraft from the surface of the central body. The arithmetic mean of the two limiting distances is the length of the axis a. The geometric mean of the two distances is the length of the semi-minor axis b, the geometric mean of the two limiting speeds is −2 ε = μ a which is the speed of a body in a circular orbit whose radius is a. The words pericenter and apocenter are often seen, although periapsis/apoapsis are preferred in technical usage, various related terms are used for other celestial objects. The -gee, -helion and -astron and -galacticon forms are used in the astronomical literature when referring to the Earth, Sun, stars. The suffix -jove is occasionally used for Jupiter, while -saturnium has very rarely used in the last 50 years for Saturn. The -gee form is used as a generic closest approach to planet term instead of specifically applying to the Earth. During the Apollo program, the terms pericynthion and apocynthion were used when referring to the Moon, regarding black holes, the term peri/apomelasma was used by physicist Geoffrey A. Landis in 1998 before peri/aponigricon appeared in the scientific literature in 2002
15.
Sun
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The Sun is the star at the center of the Solar System. It is a perfect sphere of hot plasma, with internal convective motion that generates a magnetic field via a dynamo process. It is by far the most important source of energy for life on Earth. Its diameter is about 109 times that of Earth, and its mass is about 330,000 times that of Earth, accounting for about 99. 86% of the total mass of the Solar System. About three quarters of the Suns mass consists of hydrogen, the rest is mostly helium, with smaller quantities of heavier elements, including oxygen, carbon, neon. The Sun is a G-type main-sequence star based on its spectral class and it formed approximately 4.6 billion years ago from the gravitational collapse of matter within a region of a large molecular cloud. Most of this matter gathered in the center, whereas the rest flattened into a disk that became the Solar System. The central mass became so hot and dense that it eventually initiated nuclear fusion in its core and it is thought that almost all stars form by this process. The Sun is roughly middle-aged, it has not changed dramatically for more than four billion years and it is calculated that the Sun will become sufficiently large enough to engulf the current orbits of Mercury, Venus, and probably Earth. The enormous effect of the Sun on Earth has been recognized since prehistoric times, the synodic rotation of Earth and its orbit around the Sun are the basis of the solar calendar, which is the predominant calendar in use today. The English proper name Sun developed from Old English sunne and may be related to south, all Germanic terms for the Sun stem from Proto-Germanic *sunnōn. The English weekday name Sunday stems from Old English and is ultimately a result of a Germanic interpretation of Latin dies solis, the Latin name for the Sun, Sol, is not common in general English language use, the adjectival form is the related word solar. The term sol is used by planetary astronomers to refer to the duration of a solar day on another planet. A mean Earth solar day is approximately 24 hours, whereas a mean Martian sol is 24 hours,39 minutes, and 35.244 seconds. From at least the 4th Dynasty of Ancient Egypt, the Sun was worshipped as the god Ra, portrayed as a falcon-headed divinity surmounted by the solar disk, and surrounded by a serpent. In the New Empire period, the Sun became identified with the dung beetle, in the form of the Sun disc Aten, the Sun had a brief resurgence during the Amarna Period when it again became the preeminent, if not only, divinity for the Pharaoh Akhenaton. The Sun is viewed as a goddess in Germanic paganism, Sól/Sunna, in ancient Roman culture, Sunday was the day of the Sun god. It was adopted as the Sabbath day by Christians who did not have a Jewish background, the symbol of light was a pagan device adopted by Christians, and perhaps the most important one that did not come from Jewish traditions
16.
Open cluster
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An open cluster is a group of up to a few thousand stars that were formed from the same giant molecular cloud and have roughly the same age. More than 1,100 open clusters have been discovered within the Milky Way Galaxy and they are loosely bound by mutual gravitational attraction and become disrupted by close encounters with other clusters and clouds of gas as they orbit the galactic center. This can result in a migration to the body of the galaxy. Open clusters generally survive for a few hundred years, with the most massive ones surviving for a few billion years. In contrast, the more massive clusters of stars exert a stronger gravitational attraction on their members. Open clusters have been only in spiral and irregular galaxies. Young open clusters may not be contained within the cloud from which they formed. Over time, radiation pressure from the cluster will disperse the molecular cloud, typically, about 10% of the mass of a gas cloud will coalesce into stars before radiation pressure drives the rest of the gas away. Open clusters are key objects in the study of stellar evolution, because the cluster members are of similar age and chemical composition, their properties are more easily determined than they are for isolated stars. A number of clusters, such as the Pleiades, Hyades or the Alpha Persei Cluster are visible with the naked eye. Some others, such as the Double Cluster, are barely perceptible without instruments, the Wild Duck Cluster, M11, is an example. The prominent open cluster the Pleiades has been recognized as a group of stars since antiquity, while the Hyades forms part of Taurus, other open clusters were noted by early astronomers as unresolved fuzzy patches of light. The Roman astronomer Ptolemy mentions the Praesepe, the Double Cluster in Perseus, however, it would require the invention of the telescope to resolve these nebulae into their constituent stars. Indeed, in 1603 Johann Bayer gave three of these clusters designations as if they were single stars, the first person to use a telescope to observe the night sky and record his observations was the Italian scientist Galileo Galilei in 1609. When he turned the telescope toward some of the nebulous patches recorded by Ptolemy, he found they were not a single star, for Praesepe, he found more than 40 stars. Where previously observers had noted only 6-7 stars in the Pleiades, in his 1610 treatise Sidereus Nuncius, Galileo Galilei wrote, the galaxy is nothing else but a mass of innumerable stars planted together in clusters. Influenced by Galileos work, the Sicilian astronomer Giovanni Hodierna became possibly the first astronomer to use a telescope to find previously undiscovered open clusters, in 1654, he identified the objects now designated Messier 41, Messier 47, NGC2362 and NGC2451. Between 1774–1781, French astronomer Charles Messier published a catalogue of objects that had a nebulous appearance similar to comets
17.
Planets beyond Neptune
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Following the discovery of the planet Neptune in 1846, there was considerable speculation that another planet might exist beyond its orbit. In 1978, Pluto was conclusively determined to be too small for its gravity to affect the giant planets, resulting in a brief search for a tenth planet. As of March 2014, observations with the WISE telescope have ruled out the possibility of a Saturn-sized object out to 10,000 AU, and a Jupiter-sized or larger object out to 26,000 AU. In 2016 further work showed this unknown distant planet is likely on an inclined, eccentric orbit that goes no closer than about 200 AU, the orbit is predicted to be anti-aligned to the clustered extreme trans-Neptunian objects. Because Pluto is no longer considered a planet by the International Astronomical Union, Le Verrier predicted the position of this new planet and sent his calculations to German astronomer Johann Gottfried Galle. On 23 September 1846, the following his receipt of the letter, Galle and his student Heinrich dArrest discovered Neptune. There remained some slight discrepancies in the giant planets orbits and these were taken to indicate the existence of yet another planet orbiting beyond Neptune. Even before Neptunes discovery, some speculated that one alone was not enough to explain the discrepancy. Hansens opinion was that a body could not adequately explain the motion of Uranus. In 1848, Jacques Babinet raised an objection to Le Verriers calculations, claiming that Neptunes observed mass was smaller and its orbit larger than Le Verrier had initially predicted. He postulated, based largely on simple subtraction from Le Verriers calculations, that another planet of roughly 12 Earth masses, which he named Hyperion, must exist beyond Neptune. Le Verrier denounced Babinets hypothesis, saying, absolutely nothing by which one could determine the position of another planet, astronomer George Forbes concluded on the basis of this evidence that two planets must exist beyond Neptune. These elements concorded suggestively with those made independently by another astronomer named David Peck Todd, however, sceptics argued that the orbits of the comets involved were still too uncertain to produce meaningful results. In 1900 and 1901, Harvard College Observatory director William Henry Pickering led two searches for trans-Neptunian planets, the second was launched when Gabriel Dallet suggested that a single trans-Neptunian planet lying at 47 AU could account for the motion of Uranus. Pickering agreed to examine plates for any suspected planets, in neither case were any found. In 1909, Thomas Jefferson Jackson See, an astronomer with a reputation as a contrarian, opined that there is certainly one. Tentatively naming the first planet Oceanus, he placed their respective distances at 42,56 and 72 AU from the Sun and he gave no indication as to how he determined their existence, and no known searches were mounted to locate them. In 1911, Indian astronomer Venkatesh P, the three inner Galilean moons of Jupiter, Io, Europa and Ganymede, are locked in a complicated 1,2,4 resonance called a Laplace resonance
18.
Kuiper belt
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It is similar to the asteroid belt, but it is far larger—20 times as wide and 20 to 200 times as massive. Like the asteroid belt, it consists mainly of small bodies, although many asteroids are composed primarily of rock and metal, most Kuiper belt objects are composed largely of frozen volatiles, such as methane, ammonia and water. The Kuiper belt is home to three officially recognized dwarf planets, Pluto, Haumea, and Makemake, some of the Solar Systems moons, such as Neptunes Triton and Saturns Phoebe, are also thought to have originated in the region. The Kuiper belt was named after Dutch-American astronomer Gerard Kuiper, though he did not actually predict its existence, in 1992,1992 QB1 was discovered, the first Kuiper belt object since Pluto. Since its discovery, the number of known KBOs has increased to over a thousand, the Kuiper belt should not be confused with the theorized Oort cloud, which is a thousand times more distant and is mostly spherical. The objects within the Kuiper belt, together with the members of the scattered disc, Pluto is the largest and most-massive member of the Kuiper belt and the largest and the second-most-massive known TNO, surpassed only by Eris in the scattered disc. Originally considered a planet, Plutos status as part of the Kuiper belt caused it to be reclassified as a planet in 2006. It is compositionally similar to other objects of the Kuiper belt, and its orbital period is characteristic of a class of KBOs, known as plutinos. After the discovery of Pluto in 1930, many speculated that it not be alone. The region now called the Kuiper belt was hypothesized in various forms for decades and it was only in 1992 that the first direct evidence for its existence was found. The number and variety of speculations on the nature of the Kuiper belt have led to continued uncertainty as to who deserves credit for first proposing it. The first astronomer to suggest the existence of a population was Frederick C. That same year, astronomer Armin O. Leuschner suggested that Pluto may be one of many long-period planetary objects yet to be discovered. Kuiper was operating on the common in his time that Pluto was the size of Earth and had therefore scattered these bodies out toward the Oort cloud or out of the Solar System. Were Kuipers hypothesis correct, there would not be a Kuiper belt today, the hypothesis took many other forms in the following decades. Cameron postulated the existence of a mass of small material on the outskirts of the solar system. Observation, however, ruled out this hypothesis, in 1977, Charles Kowal discovered 2060 Chiron, an icy planetoid with an orbit between Saturn and Uranus. He used a blink comparator, the device that had allowed Clyde Tombaugh to discover Pluto nearly 50 years before
19.
Planet Nine
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Planet Nine does not have an official name, and it will not receive one unless its existence is confirmed, typically through optical imaging. Once confirmed, the IAU will certify a name, with priority given to a name proposed by its discoverers. It will likely be a name chosen from Roman or Greek mythology, in their original paper, Batygin and Brown simply referred to the object as perturber, and only in later press releases did they use Planet Nine. They have also used the names Jehoshaphat and George for Planet Nine, Brown has stated, We actually call it Phattie when were just talking to each other. Planet Nine is hypothesized to follow an elliptical orbit around the Sun, with an orbital period of 10. The period with which it goes around the sun is a multiple of the periods of all the furthest Kuiper Belt objects. The high eccentricity of Planet Nines orbit could take it as far away as 1,200 AU at its aphelion. Brown thinks that if Planet Nine is confirmed to exist, a probe could fly by it in as little as 20 years, the planet is estimated to have 10 times the mass and two to four times the diameter of Earth. An object with the diameter as Neptune has not been excluded by previous surveys. An infrared survey by the Wide-field Infrared Survey Explorer in 2009 allowed for a Neptune-sized object beyond 700 AU. Using a metric based on work by Jean-Luc Margot, Brown calculated that only at the smallest size and farthest distance was it on the border of being called a dwarf planet. Brown speculates that the planet is most likely an ejected ice giant, similar in composition to Uranus and Neptune. Attempts to detect planets beyond Neptune by indirect means such as orbital perturbation date back beyond the discovery of Pluto. That could have been another planet, it could have been a star that came close to the Sun, later in 2015, they also proposed that the Centaurs with large semi-major axis are also being pushed around by the putative planet. Gomes argued that a new planet was the probable of the possible explanations. The initial argument for the existence of a planet beyond Neptune was published in 2014 by astronomers Chad Trujillo, in a later work announcing the discovery of several more distant objects Trujillo and Sheppard noted a correlation between the longitude of perihelion and the argument of perihelion of these objects. Those with a longitude of perihelion of 0–120° have arguments of perihelion between 280–360°, and those with longitude of perihelion of 180–340° have argument of perihelion 0–40° and they found a statistical significance of this correlation of 99. 99%. It was a proof of concept simulation that did not obtain a unique orbit for the planet as they state there are many possible orbital configurations the planet could have
20.
Argument of periapsis
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The argument of periapsis, symbolized as ω, is one of the orbital elements of an orbiting body. Parametrically, ω is the angle from the ascending node to its periapsis. For specific types of orbits, words such as perihelion, perigee, periastron, an argument of periapsis of 0° means that the orbiting body will be at its closest approach to the central body at the same moment that it crosses the plane of reference from South to North. An argument of periapsis of 90° means that the body will reach periapsis at its northmost distance from the plane of reference. Adding the argument of periapsis to the longitude of the ascending node gives the longitude of the periapsis, however, especially in discussions of binary stars and exoplanets, the terms longitude of periapsis or longitude of periastron are often used synonymously with argument of periapsis. In the case of equatorial orbits, the argument is strictly undefined, where, ex and ey are the x- and y-components of the eccentricity vector e. In the case of circular orbits it is assumed that the periapsis is placed at the ascending node. Kepler orbit Orbital mechanics Orbital node
21.
Neptune
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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 planet. Neptune is 17 times the mass of Earth and is more massive than its near-twin Uranus. Neptune orbits the Sun once every 164.8 years at a distance of 30.1 astronomical units. It is named after the Roman god of the sea and has the astronomical symbol ♆, Neptune is not visible to the unaided eye and is the only planet in the Solar System found by mathematical prediction rather than by empirical observation. Unexpected changes in the orbit of Uranus led Alexis Bouvard to deduce that its orbit was subject to perturbation by an unknown planet. Neptune was subsequently observed with a telescope on 23 September 1846 by Johann Galle within a degree of the predicted by Urbain Le Verrier. Its largest moon, Triton, was discovered shortly thereafter, though none of the remaining known 14 moons were located telescopically until the 20th century. The planets distance from Earth gives it a small apparent size. Neptune was visited by Voyager 2, when it flew by the planet on 25 August 1989, the advent of the Hubble Space Telescope and large ground-based telescopes with adaptive optics has recently allowed for additional detailed observations from afar. Neptunes composition can be compared and contrasted with the Solar Systems other giant planets, however, its interior, like that of Uranus, is primarily composed of ices and rock, which is why Uranus and Neptune are normally considered ice giants to emphasise this distinction. Traces of methane in the outermost regions in part account for the blue appearance. In contrast to the hazy, relatively featureless atmosphere of Uranus, Neptunes atmosphere has active, for example, at the time of the Voyager 2 flyby in 1989, the planets southern hemisphere had a Great Dark Spot comparable to the Great Red Spot on Jupiter. These weather patterns are driven by the strongest sustained winds of any planet in the Solar System, because of its great distance from the Sun, Neptunes outer atmosphere is one of the coldest places in the Solar System, with temperatures at its cloud tops approaching 55 K. Temperatures at the centre are approximately 5,400 K. Neptune has a faint and fragmented ring system. On both occasions, Galileo seems to have mistaken Neptune for a star when it appeared close—in conjunction—to Jupiter in the night sky, hence. At his first observation in December 1612, Neptune was almost stationary in the sky because it had just turned retrograde that day and this apparent backward motion is created when Earths orbit takes it past an outer planet. Because Neptune was only beginning its yearly cycle, the motion of the planet was far too slight to be detected with Galileos small telescope
22.
Apparent magnitude
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The apparent magnitude of a celestial object is a number that is a measure of its brightness as seen by an observer on Earth. The brighter an object appears, the lower its magnitude value, the Sun, at apparent magnitude of −27, is the brightest object in the sky. It is adjusted to the value it would have in the absence of the atmosphere, furthermore, the magnitude scale is logarithmic, a difference of one in magnitude corresponds to a change in brightness by a factor of 5√100, or about 2.512. The measurement of apparent magnitudes or brightnesses of celestial objects is known as photometry, apparent magnitudes are used to quantify the brightness of sources at ultraviolet, visible, and infrared wavelengths. An apparent magnitude is measured in a specific passband corresponding to some photometric system such as the UBV system. In standard astronomical notation, an apparent magnitude in the V filter band would be denoted either as mV or often simply as V, the scale used to indicate magnitude originates in the Hellenistic practice of dividing stars visible to the naked eye into six magnitudes. The brightest stars in the sky were said to be of first magnitude, whereas the faintest were of sixth magnitude. Each grade of magnitude was considered twice the brightness of the following grade and this rather crude scale for the brightness of stars was popularized by Ptolemy in his Almagest, and is generally believed to have originated with Hipparchus. This implies that a star of magnitude m is 2.512 times as bright as a star of magnitude m +1 and this figure, the fifth root of 100, became known as Pogsons Ratio. The zero point of Pogsons scale was defined by assigning Polaris a magnitude of exactly 2. However, with the advent of infrared astronomy it was revealed that Vegas radiation includes an Infrared excess presumably due to a disk consisting of dust at warm temperatures. At shorter wavelengths, there is negligible emission from dust at these temperatures, however, in order to properly extend the magnitude scale further into the infrared, this peculiarity of Vega should not affect the definition of the magnitude scale. Therefore, the scale was extrapolated to all wavelengths on the basis of the black body radiation curve for an ideal stellar surface at 11000 K uncontaminated by circumstellar radiation. On this basis the spectral irradiance for the zero magnitude point, with the modern magnitude systems, brightness over a very wide range is specified according to the logarithmic definition detailed below, using this zero reference. In practice such apparent magnitudes do not exceed 30, astronomers have developed other photometric zeropoint systems as alternatives to the Vega system. The AB magnitude zeropoint is defined such that an objects AB, the dimmer an object appears, the higher the numerical value given to its apparent magnitude, with a difference of 5 magnitudes corresponding to a brightness factor of exactly 100. Since an increase of 5 magnitudes corresponds to a decrease in brightness by a factor of exactly 100, each magnitude increase implies a decrease in brightness by the factor 5√100 ≈2.512. Inverting the above formula, a magnitude difference m1 − m2 = Δm implies a brightness factor of F2 F1 =100 Δ m 5 =100.4 Δ m ≈2.512 Δ m
23.
(474640) 2004 VN112
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2004 VN112, provisional designation 2004 VN112, is a detached object. It never gets closer than 47 AU from the Sun and averages more than 300 AU from the Sun and its large eccentricity strongly suggests that it was gravitationally scattered onto its current orbit. Because it is, like all detached objects, outside of the current gravitational influence of Neptune,2004 VN112 was discovered by the ESSENCE supernova survey on November 6,2004 observing with the 4 m Blanco Telescope from Cerro Tololo Inter-American Observatory. Its orbit is characterized by high eccentricity, moderate inclination and an axis of 316 AU. Upon discovery, it was classified as a trans-Neptunian object and its orbit is well determined, as of January 11,2017 its orbital solution is based on 34 observations spanning a data-arc of 5821 days. 2004 VN112 has a magnitude of 6.5 which gives a characteristic diameter of 130 to 300 km for an assumed albedo in the range 0. 25–0.05. Michael Browns website lists it as a dwarf planet with a diameter of 314 kilometres based on an assumed albedo of 0.04. The albedo is expected to be low because the object has a blue color, however, if the albedo is higher, the object could easily be half that size. 2004 VN112 was observed by the Hubble Space Telescope in November 2008 and it reached perihelion in 2009 and is currently 47.7 AU from the Sun. It will be in the constellation of Cetus until 2019 and it comes to opposition at the start of November. 2004 VN112s orbit is similar to that of 2013 RF98, indicating that they may have both been thrown onto the orbit by the body, or that they may have been the same object at one point. 2004 VN112s visible spectrum is different from that of 90377 Sedna. The value of its spectral slope suggests that the surface of object can have pure methane ices and highly processed carbons. Its spectral slope is similar to that of 2013 RF98 and this minor planet is one of a number of objects discovered in the Solar System to have a semi-major axis >150 AU, a perihelion beyond Neptune, and an argument of perihelion of 340 ± 55°. Of these, only eight, including 2004 VN112, have perihelia beyond Neptunes current influence
24.
(225088) 2007 OR10
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2007 OR10 is a trans-Neptunian object orbiting the Sun in the scattered disc, approximately 1500 kilometers in diameter. It is the third-largest known body in the Solar System past the orbit of Neptune, according to current estimates as of May 2016, it is slightly larger than Makemake or Haumea, and is hence almost certainly a dwarf planet. 2007 OR10 was discovered by California Institute of Technology astronomers as part of the PhD thesis of Megan E. Schwamb, Brown nicknamed the object Snow White for its presumed white color, because it would have to be very large or very bright to be detected by their survey. It was also the seventh dwarf discovered by Browns team, after Quaoar in 2002, Sedna in 2003, Haumea and Orcus in 2004, and Makemake and Eris in 2005. However,2007 OR10 turned out to be one of the reddest objects in the Kuiper belt, comparable only to Quaoar,2007 OR10 is currently the largest known object in the Solar System without an official name. However, as of 2015, Brown had yet to propose a name,2007 OR10 came to perihelion around 1857. As of February 2016 it is located 87.5 AU from the Sun and this makes it the third-farthest known large body in the Solar System, after V774104 and Eris, and farther out than Sedna. It has been farther from the Sun than Sedna since 2013,2007 OR10 will be farther than both Sedna and Eris by 2045, and it will reach aphelion in 2130. The size of an object can be calculated from its absolute magnitude,2007 OR10 has an absolute magnitude of 1.92, which makes it the fifth-brightest TNO known, a little less bright than Sedna and brighter than Orcus. 2007 OR10 is among the reddest objects known and this is probably in part due to methane frosts, which turn red when bombarded by sunlight and cosmic rays. The spectrum of 2007 OR10 shows signatures for both ice and methane, which makes it similar in composition to Quaoar. The presence of red methane frost on the surfaces of both 2007 OR10 and Quaoar implies the existence of a methane atmosphere on both objects, slowly evaporating into space. Although 2007 OR10 comes closer to the Sun than Quaoar, and is warm enough that a methane atmosphere should evaporate. In particular,2007 OR10s large size means that it is likely to retain even nitrogen, the presence of water ice on the surface of 2007 OR10 implies a brief period of cryovolcanism in its distant past. The Deep Ecliptic Survey shows the orbit to be in a 3,10 resonance with Neptune, the MPC lists it as a scattered-disc object. 2007 OR10 was discovered when searching for objects in the region of Sedna,2007 OR10 has been observed 46 times over seven oppositions with a precovery image from 1985. It was formally announced on 7 January 2009, the IAU has not addressed the possibility of accepting additional dwarf planets since before the discovery of 2007 OR10 was announced. If the orbit of OR10s small satellite can be determined, its mass could be calculated directly
25.
Eris (dwarf planet)
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Eris is the most massive and second-largest dwarf planet known in the Solar System. It is also the known body directly orbiting the Sun. It is measured to be 2,326 ±12 kilometers in diameter, Eris is 27% more massive than dwarf planet Pluto, though Pluto is slightly larger by volume. Eris mass is about 0. 27% of the Earths mass, Eris was discovered in January 2005 by a Palomar Observatory-based team led by Mike Brown, and its identity was verified later that year. It is an object and a member of a high-eccentricity population known as the scattered disk. It has one moon, Dysnomia. As of February 2016, its distance from the Sun is 96.3 astronomical units, because Eris appeared to be larger than Pluto, NASA initially described it as the Solar Systems tenth planet. This, along with the prospect of other objects of similar size being discovered in the future, motivated the International Astronomical Union to define the term planet for the first time. Observations of an occultation by Eris in 2010 showed that its diameter was 2,326 ±12 kilometers, very slightly less than Pluto. Eris was discovered by the team of Mike Brown, Chad Trujillo, the discovery was announced on July 29,2005, the same day as Makemake and two days after Haumea, due in part to events that would later lead to controversy about Haumea. Routine observations were taken by the team on October 21,2003, in January 2005, the re-analysis revealed Eriss slow motion against the background stars. Follow-up observations were carried out to make a preliminary determination of Eriss orbit. More observations released in October 2005 revealed that Eris has a moon, observations of Dysnomias orbit permitted scientists to determine the mass of Eris, which in June 2007 they calculated to be ×1022 kg, 27%±2% greater than Plutos. Eris is named after the Greek goddess Eris, a personification of strife, the regular adjectival form of Eris is Eridian. As a result, for a time the object known to the wider public as Xena. Xena was a name used internally by the discovery team. It was inspired by the character of the television series Xena. The discovery team had saved the nickname Xena for the first body they discovered that was larger than Pluto
26.
Chadwick A. Trujillo
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Chadwick A. Chad Trujillo is an American astronomer, discoverer of minor planets and the co-discoverer of Eris, the most massive dwarf planet known in the Solar System. Trujillo works with software and has examined the orbits of the numerous trans-Neptunian objects. In late August 2005, it was announced that Trujillo, along with Michael E. Brown, as a result of the discovery of the satellite Dysnomia, Eris was the first TNO known to be more massive than Pluto. Trujillo attended Oak Park and River Forest High School in Oak Park, Trujillo was later a postdoctoral scholar at Caltech, and is currently an astronomer at the Gemini Observatory in Hawaii. He studies the Kuiper belt and the outer Solar System, the main-belt asteroid 12101 Trujillo is named for him. Trujillo is credited by the Minor Planet Center with the discovery and co-discovery of 50 numbered minor planets between 1996 and 2007, including many trans-Neptunian objects from the Kuiper belt, makemake, co-discovered with Brown and Rabinowitz in 2005, one of the first 5 official dwarf planets
27.
PubMed Identifier
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PubMed is a free search engine accessing primarily the MEDLINE database of references and abstracts on life sciences and biomedical topics. The United States National Library of Medicine at the National Institutes of Health maintains the database as part of the Entrez system of information retrieval, from 1971 to 1997, MEDLINE online access to the MEDLARS Online computerized database primarily had been through institutional facilities, such as university libraries. PubMed, first released in January 1996, ushered in the era of private, free, home-, the PubMed system was offered free to the public in June 1997, when MEDLINE searches via the Web were demonstrated, in a ceremony, by Vice President Al Gore. Information about the journals indexed in MEDLINE, and available through PubMed, is found in the NLM Catalog. As of 5 January 2017, PubMed has more than 26.8 million records going back to 1966, selectively to the year 1865, and very selectively to 1809, about 500,000 new records are added each year. As of the date,13.1 million of PubMeds records are listed with their abstracts. In 2016, NLM changed the system so that publishers will be able to directly correct typos. Simple searches on PubMed can be carried out by entering key aspects of a subject into PubMeds search window, when a journal article is indexed, numerous article parameters are extracted and stored as structured information. Such parameters are, Article Type, Secondary identifiers, Language, publication type parameter enables many special features. As these clinical girish can generate small sets of robust studies with considerable precision, since July 2005, the MEDLINE article indexing process extracts important identifiers from the article abstract and puts those in a field called Secondary Identifier. The secondary identifier field is to store numbers to various databases of molecular sequence data, gene expression or chemical compounds. For clinical trials, PubMed extracts trial IDs for the two largest trial registries, ClinicalTrials. gov and the International Standard Randomized Controlled Trial Number Register, a reference which is judged particularly relevant can be marked and related articles can be identified. If relevant, several studies can be selected and related articles to all of them can be generated using the Find related data option, the related articles are then listed in order of relatedness. To create these lists of related articles, PubMed compares words from the title and abstract of each citation, as well as the MeSH headings assigned, using a powerful word-weighted algorithm. The related articles function has been judged to be so precise that some researchers suggest it can be used instead of a full search, a strong feature of PubMed is its ability to automatically link to MeSH terms and subheadings. Examples would be, bad breath links to halitosis, heart attack to myocardial infarction, where appropriate, these MeSH terms are automatically expanded, that is, include more specific terms. Terms like nursing are automatically linked to Nursing or Nursing and this important feature makes PubMed searches automatically more sensitive and avoids false-negative hits by compensating for the diversity of medical terminology. The My NCBI area can be accessed from any computer with web-access, an earlier version of My NCBI was called PubMed Cubby
28.
Michael E. Brown
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Michael E. Brown is an American astronomer, who has been professor of planetary astronomy at the California Institute of Technology since 2003. His team has discovered many objects, notably the dwarf planet Eris. He is the author of How I Killed Pluto and Why It Had It Coming and he earned his A. B. in physics from Princeton University in 1987, where he was a member of the Princeton Tower Club. He did his studies at the University of California, Berkeley where he earned an M. A. degree in astronomy in 1990. Brown is well known in the community for his surveys for distant objects orbiting the Sun. His team has discovered many trans-Neptunian objects, Browns team famously named Eris and its moon Dysnomia with the informal names Xena and Gabrielle, respectively, after the two main characters of Xena, Warrior Princess. Brown originally indicated his support for Ortizs team being given credit for the discovery of Haumea, however, the Minor Planet Center only needs precise enough orbit determination on the object in order to provide discovery credit, which Ortiz provided. The then director of the IAA, José Carlos del Toro, distanced himself from Ortiz, Brown petitioned the International Astronomical Union to credit his team rather than Ortiz as the discoverers of Haumea. The IAU has deliberately not acknowledged a discoverer of Haumea, the discovery date and location are listed as March 7,2003 at Ortizs Sierra Nevada Observatory. However, the IAU accepted Browns suggested name of Haumea, which fit the names of Haumeas two moons, rather than Ortizs Ataecina. In January 2016, Brown and fellow Caltech astronomer, Konstantin Batygin, proposed the existence of Planet Nine, the two astronomers gave a recorded interview in which they described their method and reasoning for proposing Planet 9 on January 20,2016. In 2010 Brown published a memoir of his discoveries and surrounding family life, How I Killed Pluto, Brown was named one of Times 100 most influential people of 2006. In 2007 he received Caltechs annual Feynman Prize, Caltechs most prestigious teaching honor, asteroid 11714 Mikebrown, discovered on 28 April 1998, was named in his honor. In 2012, Brown was awarded the Kavli Prize in Astrophysics, Brown married Diane Binney on March 1,2003. They have one daughter, Lilah Binney Brown and he is likes being known as the Pluto Killer so uses the Twitter handle plutokiller. Konstantin Batygin Planet Nine Notes References Wilkinson, Alex
29.
ArXiv
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In many fields of mathematics and physics, almost all scientific papers are self-archived on the arXiv repository. Begun on August 14,1991, arXiv. org passed the half-million article milestone on October 3,2008, by 2014 the submission rate had grown to more than 8,000 per month. The arXiv was made possible by the low-bandwidth TeX file format, around 1990, Joanne Cohn began emailing physics preprints to colleagues as TeX files, but the number of papers being sent soon filled mailboxes to capacity. Additional modes of access were added, FTP in 1991, Gopher in 1992. The term e-print was quickly adopted to describe the articles and its original domain name was xxx. lanl. gov. Due to LANLs lack of interest in the rapidly expanding technology, in 1999 Ginsparg changed institutions to Cornell University and it is now hosted principally by Cornell, with 8 mirrors around the world. Its existence was one of the factors that led to the current movement in scientific publishing known as open access. Mathematicians and scientists regularly upload their papers to arXiv. org for worldwide access, Ginsparg was awarded a MacArthur Fellowship in 2002 for his establishment of arXiv. The annual budget for arXiv is approximately $826,000 for 2013 to 2017, funded jointly by Cornell University Library, annual donations were envisaged to vary in size between $2,300 to $4,000, based on each institution’s usage. As of 14 January 2014,174 institutions have pledged support for the period 2013–2017 on this basis, in September 2011, Cornell University Library took overall administrative and financial responsibility for arXivs operation and development. Ginsparg was quoted in the Chronicle of Higher Education as saying it was supposed to be a three-hour tour, however, Ginsparg remains on the arXiv Scientific Advisory Board and on the arXiv Physics Advisory Committee. The lists of moderators for many sections of the arXiv are publicly available, additionally, an endorsement system was introduced in 2004 as part of an effort to ensure content that is relevant and of interest to current research in the specified disciplines. Under the system, for categories that use it, an author must be endorsed by an established arXiv author before being allowed to submit papers to those categories. Endorsers are not asked to review the paper for errors, new authors from recognized academic institutions generally receive automatic endorsement, which in practice means that they do not need to deal with the endorsement system at all. However, the endorsement system has attracted criticism for allegedly restricting scientific inquiry, perelman appears content to forgo the traditional peer-reviewed journal process, stating, If anybody is interested in my way of solving the problem, its all there – let them go and read about it. The arXiv generally re-classifies these works, e. g. in General mathematics, papers can be submitted in any of several formats, including LaTeX, and PDF printed from a word processor other than TeX or LaTeX. The submission is rejected by the software if generating the final PDF file fails, if any image file is too large. ArXiv now allows one to store and modify an incomplete submission, the time stamp on the article is set when the submission is finalized
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University of Texas at Austin
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Founded in 1881 as The University of Texas, its campus is in Austin, Texas—approximately 1 mile from the Texas State Capitol. The institution has the nations seventh-largest single-campus enrollment, with over 50,000 undergraduate and graduate students and over 24,000 faculty, UT Austin was inducted into the American Association of Universities in 1929, becoming only the third university in the American South to be elected. It is a center for academic research, with research expenditures exceeding $550 million for the 2014–2015 school year. J. Pickle Research Campus and the McDonald Observatory, among university faculty are recipients of the Nobel Prize, Pulitzer Prize, the Wolf Prize, the Emmy Award, the Turing Award, and the National Medal of Science, as well as many other awards. UT Austin student athletes compete as the Texas Longhorns and are members of the Big 12 Conference and its Longhorn Network is the only sports network featuring the college sports of a single university. The first mention of a university in Texas can be traced to the 1827 constitution for the Mexican state of Coahuila y Tejas. Although Title 6, Article 217 of the Constitution promised to establish education in the arts and sciences. On April 18,1838, An Act to Establish the University of Texas was referred to a committee of the Texas Congress. On January 26,1839, the Texas Congress agreed to set aside fifty leagues of land towards the establishment of a publicly funded university, in addition,40 acres in the new capital of Austin were reserved and designated College Hill. In 1845, Texas was annexed into the United States, interestingly, the states Constitution of 1845 failed to mention higher education. On February 11,1858, the Seventh Texas Legislature approved O. B,102, an act to establish the University of Texas, which set aside $100,000 in United States bonds toward construction of the states first publicly funded university. The legislature also designated land reserved for the encouragement of railroad construction toward the universitys endowment, Texas secession from the Union and the American Civil War delayed repayment of the borrowed monies. At the end of the Civil War in 1865, The University of Texas endowment was just over $16,000 in warrants, the more valuable lands reverted to the fund to support general education in the state. The legislature additionally appropriated $256,272.57 to repay the funds taken from the university in 1860 to pay for frontier defense, the 1883 grant of land increased the land in the Permanent University Fund to almost 2.2 million acres. Under the Act of 1858, the university was entitled to just over 1,000 acres of land for every mile of railroad built in the state. On March 30,1881, the legislature set forth the structure and organization. By popular election on September 6,1881, Austin was chosen as the site, galveston, having come in second in the election was designated the location of the medical department. On November 17,1882, on the original College Hill, smite the earth, smite the rocks with the rod of knowledge and fountains of unstinted wealth will gush forth
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The Astronomical Journal
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The Astronomical Journal is a peer-reviewed monthly scientific journal owned by the American Astronomical Society and currently published by IOP Publishing. It is one of the journals for astronomy in the world. Until 2008, the journal was published by the University of Chicago Press on behalf of the American Astronomical Society, the other two publications of the society, the Astrophysical Journal and its supplement series, followed in January 2009. The journal was established in 1849 by Benjamin A. Gould and it ceased publication in 1861 due to the American Civil War, but resumed in 1885. Between 1909 and 1941 the journal was edited in Albany, New York, in 1941, editor Benjamin Boss arranged to transfer responsibility for the journal to the American Astronomical Society. The first electronic edition of The Astronomical Journal was published in January,1998, with the July,2006 issue, The Astronomical Journal began e-first publication, an electronic version of the journal released independently of the hardcopy issues. Its current editor-in-chief is John Gallagher III, 2005–present John Gallagher III 1984–2004 Paul W. Hodge 1980–1983 N. H. Baker 1975–1979 N. H. Baker and L. B. The Astronomical Almanac Official website Dudley Observatory, The Astronomical Journal Scanned issues from ADS
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Sky & Telescope
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The articles are intended for the informed lay reader and include detailed discussions of current discoveries, frequently by participating scientists. The magazine is illustrated in color, with both amateur and professional photography of celestial sights, as well as tables and charts of upcoming celestial events. In 2005, Sky Publishing Corporation was acquired by New Track Media, in 2014, New Track was sold to F+W Media. The magazine played an important role in the dissemination of knowledge about telescope making, Amateur astronomy Amateur telescope making Official website
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Dwarf planet
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A dwarf planet is a planetary-mass object that is neither a planet nor a natural satellite. The International Astronomical Union currently recognizes five dwarf planets, Ceres, Pluto, Haumea, Makemake, another hundred or so known objects in the Solar System are suspected to be dwarf planets. Individual astronomers recognize several of these, and in August 2011 Mike Brown published a list of 390 candidate objects, Stern states that there are more than a dozen known dwarf planets. Only two of these bodies, Ceres and Pluto, have observed in enough detail to demonstrate that they actually fit the IAUs definition. The IAU accepted Eris as a dwarf planet because it is more massive than Pluto and they subsequently decided that unnamed trans-Neptunian objects with an absolute magnitude brighter than +1 are to be named under the assumption that they are dwarf planets. The classification of bodies in other systems with the characteristics of dwarf planets has not been addressed. Starting in 1801, astronomers discovered Ceres and other bodies between Mars and Jupiter which were for some decades considered to be planets. Between then and around 1851, when the number of planets had reached 23, astronomers started using the asteroid for the smaller bodies. With the discovery of Pluto in 1930, most astronomers considered the Solar System to have nine planets and it was roughly one-twentieth the mass of Mercury, which made Pluto by far the smallest planet. Although it was more than ten times as massive as the largest object in the asteroid belt, Ceres. In the 1990s, astronomers began to find objects in the region of space as Pluto. Many of these shared several of Plutos key orbital characteristics, and Pluto started being seen as the largest member of a new class of objects and this led some astronomers to stop referring to Pluto as a planet. Several terms, including subplanet and planetoid, started to be used for the now known as dwarf planets. By 2005, three trans-Neptunian objects comparable in size to Pluto had been reported and it became clear that either they would also have to be classified as planets, or Pluto would have to be reclassified. Astronomers were also confident that more objects as large as Pluto would be discovered, Eris was discovered in January 2005, it was thought to be slightly larger than Pluto, and some reports informally referred to it as the tenth planet. As a consequence, the became a matter of intense debate during the IAU General Assembly in August 2006. The IAUs initial draft proposal included Charon, Eris, and Ceres in the list of planets, dropping Charon from the list, the new proposal also removed Pluto, Ceres, and Eris, because they have not cleared their orbits. The IAUs final Resolution 5A preserved this three-category system for the bodies orbiting the Sun
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Asteroid belt
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The asteroid belt is the circumstellar disc in the Solar System located roughly between the orbits of the planets Mars and Jupiter. It is occupied by numerous irregularly shaped bodies called asteroids or minor planets, the asteroid belt is also termed the main asteroid belt or main belt to distinguish it from other asteroid populations in the Solar System such as near-Earth asteroids and trojan asteroids. About half the mass of the belt is contained in the four largest asteroids, Ceres, Vesta, Pallas, the total mass of the asteroid belt is approximately 4% that of the Moon, or 22% that of Pluto, and roughly twice that of Plutos moon Charon. Ceres, the belts only dwarf planet, is about 950 km in diameter, whereas Vesta, Pallas. The remaining bodies range down to the size of a dust particle, the asteroid material is so thinly distributed that numerous unmanned spacecraft have traversed it without incident. Nonetheless, collisions between large asteroids do occur, and these can form a family whose members have similar orbital characteristics. Individual asteroids within the belt are categorized by their spectra. The asteroid belt formed from the solar nebula as a group of planetesimals. Planetesimals are the precursors of the protoplanets. Between Mars and Jupiter, however, gravitational perturbations from Jupiter imbued the protoplanets with too much energy for them to accrete into a planet. Collisions became too violent, and instead of fusing together, the planetesimals, as a result,99. 9% of the asteroid belts original mass was lost in the first 100 million years of the Solar Systems history. Some fragments eventually found their way into the inner Solar System, Asteroid orbits continue to be appreciably perturbed whenever their period of revolution about the Sun forms an orbital resonance with Jupiter. At these orbital distances, a Kirkwood gap occurs as they are swept into other orbits. Classes of small Solar System bodies in other regions are the objects, the centaurs, the Kuiper belt objects, the scattered disc objects, the sednoids. On 22 January 2014, ESA scientists reported the detection, for the first definitive time, of water vapor on Ceres, the detection was made by using the far-infrared abilities of the Herschel Space Observatory. The finding was unexpected because comets, not asteroids, are considered to sprout jets. According to one of the scientists, The lines are becoming more and more blurred between comets and asteroids. This pattern, now known as the Titius–Bode law, predicted the semi-major axes of the six planets of the provided one allowed for a gap between the orbits of Mars and Jupiter
. Bibcode:2004ApJ...617..645B. doi:10.1086/422095. Archived from the original (PDF) on 2006-06-27. Retrieved 2008-04-02.
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