1.
Planet
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The term planet is ancient, with ties to history, astrology, science, mythology, and religion. Several planets in the Solar System can be seen with the naked eye and these were regarded by many early cultures as divine, or as emissaries of deities. As scientific knowledge advanced, human perception of the planets changed, in 2006, the International Astronomical Union officially adopted a resolution defining planets within the Solar System. This definition is controversial because it excludes many objects of mass based on where or what they orbit. The planets were thought by Ptolemy to orbit Earth in deferent, at about the same time, by careful analysis of pre-telescopic observation data collected by Tycho Brahe, Johannes Kepler found the planets orbits were not circular but elliptical. As observational tools improved, astronomers saw that, like Earth, the planets rotated around tilted axes, and some shared such features as ice caps and seasons. Since the dawn of the Space Age, close observation by space probes has found that Earth and the planets share characteristics such as volcanism, hurricanes, tectonics. Planets are generally divided into two types, large low-density giant planets, and smaller rocky terrestrials. Under IAU definitions, there are eight planets in the Solar System, in order of increasing distance from the Sun, they are the four terrestrials, Mercury, Venus, Earth, and Mars, then the four giant planets, Jupiter, Saturn, Uranus, and Neptune. Six of the planets are orbited by one or more natural satellites, several thousands of planets around other stars have been discovered in the Milky Way. e. in the habitable zone. On December 20,2011, the Kepler Space Telescope team reported the discovery of the first Earth-sized extrasolar planets, Kepler-20e and Kepler-20f, orbiting a Sun-like star, Kepler-20. A2012 study, analyzing gravitational microlensing data, estimates an average of at least 1.6 bound planets for every star in the Milky Way, around one in five Sun-like stars is thought to have an Earth-sized planet in its habitable zone. The idea of planets has evolved over its history, from the lights of antiquity to the earthly objects of the scientific age. The concept has expanded to include not only in the Solar System. The ambiguities inherent in defining planets have led to much scientific controversy, the five classical planets, being visible to the naked eye, have been known since ancient times and have had a significant impact on mythology, religious cosmology, and ancient astronomy. In ancient times, astronomers noted how certain lights moved across the sky, as opposed to the fixed stars, ancient Greeks called these lights πλάνητες ἀστέρες or simply πλανῆται, from which todays word planet was derived. In ancient Greece, China, Babylon, and indeed all pre-modern civilizations, it was almost universally believed that Earth was the center of the Universe and that all the planets circled Earth. The first civilization known to have a theory of the planets were the Babylonians
2.
Gas
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Gas is one of the four fundamental states of matter. A pure gas may be made up of atoms, elemental molecules made from one type of atom. A gas mixture would contain a variety of pure gases much like the air, what distinguishes a gas from liquids and solids is the vast separation of the individual gas particles. This separation usually makes a colorless gas invisible to the human observer, the interaction of gas particles in the presence of electric and gravitational fields are considered negligible as indicated by the constant velocity vectors in the image. One type of commonly known gas is steam, the gaseous state of matter is found between the liquid and plasma states, the latter of which provides the upper temperature boundary for gases. Bounding the lower end of the temperature scale lie degenerative quantum gases which are gaining increasing attention, high-density atomic gases super cooled to incredibly low temperatures are classified by their statistical behavior as either a Bose gas or a Fermi gas. For a comprehensive listing of these states of matter see list of states of matter. The only chemical elements which are stable multi atom homonuclear molecules at temperature and pressure, are hydrogen, nitrogen and oxygen. These gases, when grouped together with the noble gases. Alternatively they are known as molecular gases to distinguish them from molecules that are also chemical compounds. The word gas is a neologism first used by the early 17th-century Flemish chemist J. B. van Helmont, according to Paracelsuss terminology, chaos meant something like ultra-rarefied water. An alternative story is that Van Helmonts word is corrupted from gahst and these four characteristics were repeatedly observed by scientists such as Robert Boyle, Jacques Charles, John Dalton, Joseph Gay-Lussac and Amedeo Avogadro for a variety of gases in various settings. Their detailed studies ultimately led to a relationship among these properties expressed by the ideal gas law. Gas particles are separated from one another, and consequently have weaker intermolecular bonds than liquids or solids. These intermolecular forces result from interactions between gas particles. Like-charged areas of different gas particles repel, while oppositely charged regions of different gas particles attract one another, transient, randomly induced charges exist across non-polar covalent bonds of molecules and electrostatic interactions caused by them are referred to as Van der Waals forces. The interaction of these forces varies within a substance which determines many of the physical properties unique to each gas. A comparison of boiling points for compounds formed by ionic and covalent bonds leads us to this conclusion, the drifting smoke particles in the image provides some insight into low pressure gas behavior
3.
Rock (geology)
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Rock or stone is a natural substance, a solid aggregate of one or more minerals or mineraloids. For example, granite, a rock, is a combination of the minerals quartz, feldspar. The Earths outer solid layer, the lithosphere, is made of rock, rock has been used by mankind throughout history. The minerals and metals found in rocks have been essential to human civilization, three major groups of rocks are defined, igneous, sedimentary, and metamorphic. The scientific study of rocks is called petrology, which is a component of geology. At a granular level, rocks are composed of grains of minerals, the aggregate minerals forming the rock are held together by chemical bonds. The types and abundance of minerals in a rock are determined by the manner in which the rock was formed, many rocks contain silica, a compound of silicon and oxygen that forms 74. 3% of the Earths crust. This material forms crystals with other compounds in the rock, the proportion of silica in rocks and minerals is a major factor in determining their name and properties. Rocks are geologically classified according to such as mineral and chemical composition, permeability, the texture of the constituent particles. These physical properties are the end result of the processes that formed the rocks, over the course of time, rocks can transform from one type into another, as described by the geological model called the rock cycle. These events produce three general classes of rock, igneous, sedimentary, and metamorphic, the three classes of rocks are subdivided into many groups. However, there are no hard and fast boundaries between allied rocks, hence the definitions adopted in establishing rock nomenclature merely correspond to more or less arbitrary selected points in a continuously graduated series. Igneous rock forms through the cooling and solidification of magma or lava and this magma can be derived from partial melts of pre-existing rocks in either a planets mantle or crust. Typically, the melting of rocks is caused by one or more of three processes, an increase in temperature, a decrease in pressure, or a change in composition, igneous rocks are divided into two main categories, plutonic rock and volcanic. Plutonic or intrusive rocks result when magma cools and crystallizes slowly within the Earths crust, a common example of this type is granite. Volcanic or extrusive rocks result from magma reaching the surface either as lava or fragmental ejecta, the chemical abundance and the rate of cooling of magma typically forms a sequence known as Bowens reaction series. Most major igneous rocks are found along this scale, about 64. 7% of the Earths crust by volume consists of igneous rocks, making it the most plentiful category. Of these, 66% are basalts and gabbros, 16% are granite, only 0. 6% are syenites and 0. 3% peridotites and dunites
4.
Solid
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Solid is one of the four fundamental states of matter. It is characterized by structural rigidity and resistance to changes of shape or volume, unlike a liquid, a solid object does not flow to take on the shape of its container, nor does it expand to fill the entire volume available to it like a gas does. The atoms in a solid are tightly bound to other, either in a regular geometric lattice or irregularly. The branch of physics deals with solids is called solid-state physics. Materials science is concerned with the physical and chemical properties of solids. Solid-state chemistry is concerned with the synthesis of novel materials, as well as the science of identification. The atoms, molecules or ions which make up solids may be arranged in a repeating pattern. Materials whose constituents are arranged in a regular pattern are known as crystals, in some cases, the regular ordering can continue unbroken over a large scale, for example diamonds, where each diamond is a single crystal. Almost all common metals, and many ceramics, are polycrystalline, in other materials, there is no long-range order in the position of the atoms. These solids are known as amorphous solids, examples include polystyrene, whether a solid is crystalline or amorphous depends on the material involved, and the conditions in which it was formed. Solids which are formed by slow cooling will tend to be crystalline, likewise, the specific crystal structure adopted by a crystalline solid depends on the material involved and on how it was formed. While many common objects, such as an ice cube or a coin, are chemically identical throughout, for example, a typical rock is an aggregate of several different minerals and mineraloids, with no specific chemical composition. Wood is an organic material consisting primarily of cellulose fibers embedded in a matrix of organic lignin. In materials science, composites of more than one constituent material can be designed to have desired properties, the forces between the atoms in a solid can take a variety of forms. For example, a crystal of sodium chloride is made up of sodium and chlorine. In diamond or silicon, the atoms share electrons and form covalent bonds, in metals, electrons are shared in metallic bonding. Some solids, particularly most organic compounds, are together with van der Waals forces resulting from the polarization of the electronic charge cloud on each molecule. The dissimilarities between the types of solid result from the differences between their bonding, metals typically are strong, dense, and good conductors of both electricity and heat
5.
Exoplanetology
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Exoplanetology, or exoplanetary science, is an integrated field of astronomical science dedicated to the search and study of exoplanets. It employs an approach which includes astrobiology, astrophysics, astronomy, astrochemistry, astrogeology, geochemistry. The exoplanet naming convention is an extension of the used for naming multiple-star systems as adopted by the International Astronomical Union. For exoplanets orbiting a star, the name is normally formed by taking the name of its parent star. The first planet discovered in a system is given the designation b, If several planets in the same system are discovered at the same time, the closest one to the star gets the next letter, followed by the other planets in order of orbit size. A provisional IAU-sanctioned standard exists to accommodate the naming of circumbinary planets, a limited number of exoplanets have IAU-sanctioned proper names. The IAUs working definition is not always used, one alternate suggestion is that planets should be distinguished from brown dwarfs on the basis of formation. Brown dwarfs form like stars from the collapse of clouds of gas. Most directly imaged planets as of April 2014 are massive and have wide orbits so probably represent the end of brown dwarf formation. Also, the 13-Jupiter-mass cutoff does not have physical significance. Deuterium fusion can occur in objects with a mass below that cutoff. The amount of deuterium fused depends to some extent on the composition of the object, the NASA Exoplanet Archive includes objects with a mass equal to or less than 30 Jupiter masses. Another suggestion, based on mass–density relationships, is that the line should be at 60 Jupiter masses. Planets are extremely faint compared to their parent stars, for example, a Sun-like star is about a billion times brighter than the reflected light from any exoplanet orbiting it. It is difficult to detect such a faint light source, all exoplanets that have been directly imaged are both large and widely separated from their parent star. The following are the methods that have proven useful, Transit method If a planet crosses in front of its parent stars disk. The amount by which the star depends on its size and on the size of the planet. The Kepler telescope uses this method, radial velocity or Doppler method As a planet orbits a star, the star also moves in its own small orbit around the systems center of mass
6.
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
7.
Jupiter
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Jupiter is the fifth planet from the Sun and the largest in the Solar System. It is a giant planet with a mass one-thousandth that of the Sun, Jupiter and Saturn are gas giants, the other two giant planets, Uranus and Neptune are ice giants. Jupiter has been known to astronomers since antiquity, the Romans named it after their god Jupiter. Jupiter is primarily composed of hydrogen with a quarter of its mass being helium and it may also have a rocky core of heavier elements, but like the other giant planets, Jupiter lacks a well-defined solid surface. Because of its rotation, the planets shape is that of an oblate spheroid. The outer atmosphere is visibly segregated into several bands at different latitudes, resulting in turbulence, a prominent result is the Great Red Spot, a giant storm that is known to have existed since at least the 17th century when it was first seen by telescope. Surrounding Jupiter is a faint planetary ring system and a powerful magnetosphere, Jupiter has at least 67 moons, including the four large Galilean moons discovered by Galileo Galilei in 1610. Ganymede, the largest of these, has a greater than that of the planet Mercury. Jupiter has been explored on several occasions by robotic spacecraft, most notably during the early Pioneer and Voyager flyby missions and later by the Galileo orbiter. In late February 2007, Jupiter was visited by the New Horizons probe, the latest probe to visit the planet is Juno, which entered into orbit around Jupiter on July 4,2016. Future targets for exploration in the Jupiter system include the probable ice-covered liquid ocean of its moon Europa, Earth and its neighbor planets may have formed from fragments of planets after collisions with Jupiter destroyed those super-Earths near the Sun. Astronomers have discovered nearly 500 planetary systems with multiple planets, Jupiter moving out of the inner Solar System would have allowed the formation of inner planets, including Earth. Jupiter is composed primarily of gaseous and liquid matter and it is the largest of the four giant planets in the Solar System and hence its largest planet. It has a diameter of 142,984 km at its equator, the average density of Jupiter,1.326 g/cm3, is the second highest of the giant planets, but lower than those of the four terrestrial planets. Jupiters upper atmosphere is about 88–92% hydrogen and 8–12% helium by percent volume of gas molecules, a helium atom has about four times as much mass as a hydrogen atom, so the composition changes when described as the proportion of mass contributed by different atoms. Thus, Jupiters atmosphere is approximately 75% hydrogen and 24% helium by mass, the atmosphere contains trace amounts of methane, water vapor, ammonia, and silicon-based compounds. There are also traces of carbon, ethane, hydrogen sulfide, neon, oxygen, phosphine, the outermost layer of the atmosphere contains crystals of frozen ammonia. The interior contains denser materials - by mass it is roughly 71% hydrogen, 24% helium, through infrared and ultraviolet measurements, trace amounts of benzene and other hydrocarbons have also been found
8.
Saturn
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Saturn is the sixth planet from the Sun and the second-largest in the Solar System, after Jupiter. It is a gas giant with a radius about nine times that of Earth. Although it has only one-eighth the average density of Earth, with its larger volume Saturn is just over 95 times more massive, Saturn is named after the Roman god of agriculture, its astronomical symbol represents the gods sickle. Saturns interior is composed of a core of iron–nickel and rock. This core is surrounded by a layer of metallic hydrogen, an intermediate layer of liquid hydrogen and liquid helium. Saturn has a yellow hue due to ammonia crystals in its upper atmosphere. Saturns magnetic field strength is around one-twentieth of Jupiters, the outer atmosphere is generally bland and lacking in contrast, although long-lived features can appear. Wind speeds on Saturn can reach 1,800 km/h, higher than on Jupiter, sixty-two moons are known to orbit Saturn, of which fifty-three are officially named. This does not include the hundreds of moonlets comprising the rings, Saturn is a gas giant because it is predominantly composed of hydrogen and helium. It lacks a definite surface, though it may have a solid core, Saturns rotation causes it to have the shape of an oblate spheroid, that is, it is flattened at the poles and bulges at its equator. Its equatorial and polar radii differ by almost 10%,60,268 km versus 54,364 km, Jupiter, Uranus, and Neptune, the other giant planets in the Solar System, are also oblate but to a lesser extent. Saturn is the planet of the Solar System that is less dense than water—about 30% less. Although Saturns core is considerably denser than water, the specific density of the planet is 0.69 g/cm3 due to the atmosphere. Jupiter has 318 times the Earths mass, while Saturn is 95 times the mass of the Earth, together, Jupiter and Saturn hold 92% of the total planetary mass in the Solar System. On 8 January 2015, NASA reported determining the center of the planet Saturn, the temperature, pressure, and density inside Saturn all rise steadily toward the core, which causes hydrogen to transition into a metal in the deeper layers. Standard planetary models suggest that the interior of Saturn is similar to that of Jupiter, having a rocky core surrounded by hydrogen. This core is similar in composition to the Earth, but more dense, in 2004, they estimated that the core must be 9–22 times the mass of the Earth, which corresponds to a diameter of about 25,000 km. This is surrounded by a liquid metallic hydrogen layer, followed by a liquid layer of helium-saturated molecular hydrogen that gradually transitions to a gas with increasing altitude
9.
Uranus
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Uranus is the seventh planet from the Sun. It has the third-largest planetary radius and fourth-largest planetary mass in the Solar System, Uranus is similar in composition to Neptune, and both have different bulk chemical composition from that of the larger gas giants Jupiter and Saturn. For this reason, scientists often classify Uranus and Neptune as ice giants to distinguish them from the gas giants, the interior of Uranus is mainly composed of ices and rock. Uranus is the planet whose name is derived from a figure from Greek mythology. Like the other giant planets, Uranus has a system, a magnetosphere. The Uranian system has a unique configuration among those of the planets because its axis of rotation is tilted sideways and its north and south poles, therefore, lie where most other planets have their equators. In 1986, images from Voyager 2 showed Uranus as an almost featureless planet in visible light, observations from Earth have shown seasonal change and increased weather activity as Uranus approached its equinox in 2007. Wind speeds can reach 250 metres per second, like the classical planets, Uranus is visible to the naked eye, but it was never recognised as a planet by ancient observers because of its dimness and slow orbit. Uranus had been observed on many occasions before its recognition as a planet, possibly the earliest known observation was by Hipparchos, who in 128 BCE might have recorded it as a star for his star catalogue that was later incorporated into Ptolemys Almagest. The earliest definite sighting was in 1690 when John Flamsteed observed it at least six times, the French astronomer Pierre Lemonnier observed Uranus at least twelve times between 1750 and 1769, including on four consecutive nights. Sir William Herschel observed Uranus on March 13,1781 from the garden of his house at 19 New King Street in Bath, Somerset, England, Herschel engaged in a series of observations on the parallax of the fixed stars, using a telescope of his own design. Herschel recorded in his journal, In the quartile near ζ Tauri, either Nebulous star or perhaps a comet. On March 17 he noted, I looked for the Comet or Nebulous Star and found that it is a Comet, the sequel has shown that my surmises were well-founded, this proving to be the Comet we have lately observed. Herschel notified the Astronomer Royal, Nevil Maskelyne, of his discovery and received this flummoxed reply from him on April 23,1781, I dont know what to call it. It is as likely to be a planet moving in an orbit nearly circular to the sun as a Comet moving in a very eccentric ellipsis. I have not yet seen any coma or tail to it, although Herschel continued to describe his new object as a comet, other astronomers had already begun to suspect otherwise. Finnish-Swedish astronomer Anders Johan Lexell, working in Russia, was the first to compute the orbit of the new object and its nearly circular orbit led him to a conclusion that it was a planet rather than a comet. Berlin astronomer Johann Elert Bode described Herschels discovery as a star that can be deemed a hitherto unknown planet-like object circulating beyond the orbit of Saturn
10.
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
11.
Exoplanet
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An exoplanet or extrasolar planet is a planet that orbits a star other than the Sun. The first scientific detection of an exoplanet was in 1988, HARPS has discovered about a hundred exoplanets while the Kepler space telescope has found more than two thousand. Kepler has also detected a few thousand candidate planets, of which about 11% may be false positives, on average, there is at least one planet per star, with a percentage having multiple planets. About 1 in 5 Sun-like stars have an Earth-sized planet in the habitable zone, the least massive planet known is Draugr, which is about twice the mass of the Moon. There are planets that are so near to their star that they take only a few hours to orbit, some are so far out that it is difficult to tell whether they are gravitationally bound to the star. Almost all of the planets detected so far are within the Milky Way, the nearest exoplanet is Proxima Centauri b, located 4.2 light-years from Earth and orbiting Proxima Centauri, the closest star to the Sun. The discovery of exoplanets has intensified interest in the search for extraterrestrial life, there is special interest in planets that orbit in a stars habitable zone, where it is possible for liquid water, a prerequisite for life on Earth, to exist on the surface. The study of planetary habitability also considers a range of other factors in determining the suitability of a planet for hosting life. The rogue planets in the Milky Way possibly number in the billions, the convention for designating exoplanets is an extension of the system used for designating multiple-star systems as adopted by the International Astronomical Union. For exoplanets orbiting a star, the designation is normally formed by taking the name or, more commonly, designation of its parent star. The first planet discovered in a system is given the designation b, if several planets in the same system are discovered at the same time, the closest one to the star gets the next letter, followed by the other planets in order of orbital size. A provisional IAU-sanctioned standard exists to accommodate the designation of circumbinary planets, a limited number of exoplanets have IAU-sanctioned proper names. Various detection claims made in the century were rejected by astronomers. The first scientific detection of an exoplanet began in 1988, However, the first confirmed detection came in 1992, with the discovery of several terrestrial-mass planets orbiting the pulsar PSR B1257+12. The first confirmation of an exoplanet orbiting a star was made in 1995. Some exoplanets have been imaged directly by telescopes, but the vast majority have been detected through indirect methods, such as the transit method, in the eighteenth century the same possibility was mentioned by Isaac Newton in the General Scholium that concludes his Principia. Claims of exoplanet detections have been made since the nineteenth century, some of the earliest involve the binary star 70 Ophiuchi. In 1855 William Stephen Jacob at the East India Companys Madras Observatory reported that orbital anomalies made it highly probable that there was a body in this system
12.
Star
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A star is a luminous sphere of plasma held together by its own gravity. The nearest star to Earth is the Sun, many other stars are visible to the naked eye from Earth during the night, appearing as a multitude of fixed luminous points in the sky due to their immense distance from Earth. Historically, the most prominent stars were grouped into constellations and asterisms, astronomers have assembled star catalogues that identify the known stars and provide standardized stellar designations. However, most of the stars in the Universe, including all stars outside our galaxy, indeed, most are invisible from Earth even through the most powerful telescopes. Almost all naturally occurring elements heavier than helium are created by stellar nucleosynthesis during the stars lifetime, near the end of its life, a star can also contain degenerate matter. Astronomers can determine the mass, age, metallicity, and many properties of a star by observing its motion through space, its luminosity. The total mass of a star is the factor that determines its evolution. Other characteristics of a star, including diameter and temperature, change over its life, while the environment affects its rotation. A plot of the temperature of stars against their luminosities produces a plot known as a Hertzsprung–Russell diagram. Plotting a particular star on that allows the age and evolutionary state of that star to be determined. A stars life begins with the collapse of a gaseous nebula of material composed primarily of hydrogen, along with helium. When the stellar core is sufficiently dense, hydrogen becomes steadily converted into helium through nuclear fusion, the remainder of the stars interior carries energy away from the core through a combination of radiative and convective heat transfer processes. The stars internal pressure prevents it from collapsing further under its own gravity, a star with mass greater than 0.4 times the Suns will expand to become a red giant when the hydrogen fuel in its core is exhausted. In some cases, it will fuse heavier elements at the core or in shells around the core, as the star expands it throws a part of its mass, enriched with those heavier elements, into the interstellar environment, to be recycled later as new stars. Meanwhile, the core becomes a remnant, a white dwarf. Binary and multi-star systems consist of two or more stars that are bound and generally move around each other in stable orbits. When two such stars have a close orbit, their gravitational interaction can have a significant impact on their evolution. Stars can form part of a much larger gravitationally bound structure, historically, stars have been important to civilizations throughout the world
13.
Gas giant
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A gas giant is a giant planet composed mainly of hydrogen and helium. Jupiter and Saturn are the gas giants of the Solar System, for this reason, Uranus and Neptune are now often classified in the separate category of ice giants. Jupiter and Saturn consist mostly of hydrogen and helium, with heavier elements making up between 3 and 13 percent of the mass and they are thought to consist of an outer layer of molecular hydrogen surrounding a layer of liquid metallic hydrogen, with probably a molten rocky core. The outermost portion of their hydrogen atmosphere is characterized by layers of visible clouds that are mostly composed of water. The layer of metallic hydrogen makes up the bulk of each planet, the gas giants cores are thought to consist of heavier elements at such high temperatures and pressures that their properties are poorly understood. 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, on the physics of the interior. 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 science 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 all giant 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. 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. Because Uranus and Neptune are primarily composed of, in this terminology, ices, not gas, they are referred to as ice giants. Jupiter and Saturn are both class I, hot Jupiters are class IV or V. A cold hydrogen-rich gas giant more massive than Jupiter but less than about 500 M⊕ will only be larger in volume than Jupiter. For masses above 500 M⊕, gravity will cause the planet to shrink, kelvin–Helmholtz heating can cause a gas giant to radiate more energy than it receives from its host star. Although the words gas and giant are often combined, hydrogen planets need not be as large as the gas giants from the Solar System. However, smaller gas planets and planets closer to their star will lose atmospheric mass more quickly via hydrodynamic escape than larger planets and planets farther out. The smallest known extrasolar planet that is likely a gas planet is Kepler-138d, a low-mass gas planet can still have a radius resembling that of a gas giant if it has the right temperature. List of gravitationally rounded objects of the Solar System List of planet types
14.
Ice giant
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An ice giant is a giant planet composed mainly of elements heavier than hydrogen and helium, such as oxygen, carbon, nitrogen, and sulfur. There are two ice giants in the Solar System, Uranus and Neptune. Since 2014, there has been evidence of the existence of a possible third ice giant. Ice giants consist of only about 20% hydrogen and helium in mass, as opposed to the Solar Systems gas giants, in the 1990s, it was realized that Uranus and Neptune are a distinct class of giant planet, separate from the other giant planets. The amount of volatiles within the ice giants today is, however. In 1952, science fiction writer James Blish coined the term gas giant, however, in the 1990s, the compositions of Uranus and Neptune were discovered to be significantly different from those of Jupiter and Saturn. They are primarily composed of heavier than hydrogen and helium. Because during their formation Uranus and Neptune incorporated their material as either ices or gas trapped in water ice, today, very little of the water in Uranus and Neptune remains in the form of ice. Instead, H2O primarily exists as supercritical fluid at the temperatures and pressures within them, modelling the formation of the terrestrial and gas giants is relatively straightforward and uncontroversial. The terrestrial planets of the Solar System are widely understood to have formed through accumulation of planetesimals within the protoplanetary disc. Some extrasolar giant planets may instead have formed via gravitational disk instabilities, the formation of Uranus and Neptune through a similar process of core accretion is far more problematic. The escape velocity for the small protoplanets about 20 astronomical units from the centre of the Solar System would have been comparable to their relative velocities, such bodies crossing the orbits of Saturn or Jupiter would have been liable to be sent on hyperbolic trajectories ejecting them from the system. Such bodies, being swept up by the gas giants, would also have likely to just be accreted into the larger planets or thrown into cometary orbits. In spite of the trouble modelling their formation, many ice giant candidates have been observed orbiting other stars since 2004 and this indicates that they may be common in the Milky Way. Gravitational instability of the disk could also produce several gas giant protoplanets out to distances of up to 30 AU. Slightly-higher-density regions in the disk could lead to the formation of clumps that eventually collapse to planetary densities, a disk with even marginal gravitational instability could yield protoplanets between 10 and 30 AU in over one thousand years. A problem with this model is determining what kept the disk prior to the instability. There are several possible mechanisms allowing gravitational instability to occur during disk evolution, a close encounter with another protostar could provide a gravitational kick to an otherwise stable disk
15.
Critical point (thermodynamics)
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In thermodynamics, a critical point is the end point of a phase equilibrium curve. The most prominent example is the critical point, the end point of the pressure-temperature curve that designates conditions under which a liquid. At the critical point, defined by a critical temperature Tc, other examples include the liquid–liquid critical points in mixtures. For simplicity and clarity, the notion of critical point is best introduced by discussing a specific example. This was the first critical point to be discovered, and it is still the best known, the figure to the right shows the schematic PT diagram of a pure substance. The commonly known phases solid, liquid and vapor are separated by phase boundaries, at the triple point, all three phases can coexist. However, the liquid-vapor boundary terminates in an endpoint at some critical temperature Tc, in water, the critical point occurs at around 647 K and 22.064 MPa. In the vicinity of the point, the physical properties of the liquid. For instance, liquid water under normal conditions is nearly incompressible, has a low thermal expansion coefficient, has a dielectric constant. At the critical point, only one phase exists, the heat of vaporization is zero. There is a point in the constant-temperature line on a PV diagram. This means that at the point, T = T =0 Above the critical point there exists a state of matter that is continuously connected with both the liquid and the gaseous state. The existence of a point was first discovered by Charles Cagniard de la Tour in 1822 and named by Dmitri Mendeleev in 1860. Cagniard showed that CO2 could be liquefied at 31 °C at a pressure of 73 atm, but not at a slightly higher temperature, even under pressures as high as 3,000 atm. Solving the above condition T =0 for the van der Waals equation, however, the van der Waals equation, based on a mean field theory, does not hold near the critical point. In particular, it predicts wrong scaling laws, the principle of corresponding states indicates that substances at equal reduced pressures and temperatures have equal reduced volumes. This relationship is true for many substances, but becomes increasingly inaccurate for large values of pr. The liquid–liquid critical point of a solution, which occurs at the solution temperature
16.
Hydrogen
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Hydrogen is a chemical element with chemical symbol H and atomic number 1. With a standard weight of circa 1.008, hydrogen is the lightest element on the periodic table. Its monatomic form is the most abundant chemical substance in the Universe, non-remnant stars are mainly composed of hydrogen in the plasma state. The most common isotope of hydrogen, termed protium, has one proton, the universal emergence of atomic hydrogen first occurred during the recombination epoch. At standard temperature and pressure, hydrogen is a colorless, odorless, tasteless, non-toxic, nonmetallic, since hydrogen readily forms covalent compounds with most nonmetallic elements, most of the hydrogen on Earth exists in molecular forms such as water or organic compounds. Hydrogen plays an important role in acid–base reactions because most acid-base reactions involve the exchange of protons between soluble molecules. In ionic compounds, hydrogen can take the form of a charge when it is known as a hydride. The hydrogen cation is written as though composed of a bare proton, Hydrogen gas was first artificially produced in the early 16th century by the reaction of acids on metals. Industrial production is mainly from steam reforming natural gas, and less often from more energy-intensive methods such as the electrolysis of water. Most hydrogen is used near the site of its production, the two largest uses being fossil fuel processing and ammonia production, mostly for the fertilizer market, Hydrogen is a concern in metallurgy as it can embrittle many metals, complicating the design of pipelines and storage tanks. Hydrogen gas is flammable and will burn in air at a very wide range of concentrations between 4% and 75% by volume. The enthalpy of combustion is −286 kJ/mol,2 H2 + O2 →2 H2O +572 kJ Hydrogen gas forms explosive mixtures with air in concentrations from 4–74%, the explosive reactions may be triggered by spark, heat, or sunlight. The hydrogen autoignition temperature, the temperature of spontaneous ignition in air, is 500 °C, the detection of a burning hydrogen leak may require a flame detector, such leaks can be very dangerous. Hydrogen flames in other conditions are blue, resembling blue natural gas flames, the destruction of the Hindenburg airship was a notorious example of hydrogen combustion and the cause is still debated. The visible orange flames in that incident were the result of a mixture of hydrogen to oxygen combined with carbon compounds from the airship skin. H2 reacts with every oxidizing element, the ground state energy level of the electron in a hydrogen atom is −13.6 eV, which is equivalent to an ultraviolet photon of roughly 91 nm wavelength. The energy levels of hydrogen can be calculated fairly accurately using the Bohr model of the atom, however, the atomic electron and proton are held together by electromagnetic force, while planets and celestial objects are held by gravity. The most complicated treatments allow for the effects of special relativity
17.
Helium
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Helium is a chemical element with symbol He and atomic number 2. It is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas and its boiling point is the lowest among all the elements. Its abundance is similar to figure in the Sun and in Jupiter. This is due to the high nuclear binding energy of helium-4 with respect to the next three elements after helium. This helium-4 binding energy also accounts for why it is a product of nuclear fusion and radioactive decay. Most helium in the universe is helium-4, and is believed to have formed during the Big Bang. Large amounts of new helium are being created by fusion of hydrogen in stars. Helium is named for the Greek god of the Sun, Helios and it was first detected as an unknown yellow spectral line signature in sunlight during a solar eclipse in 1868 by French astronomer Jules Janssen. Janssen is jointly credited with detecting the element along with Norman Lockyer, Janssen observed during the solar eclipse of 1868 while Lockyer observed from Britain. Lockyer was the first to propose that the line was due to a new element, the formal discovery of the element was made in 1895 by two Swedish chemists, Per Teodor Cleve and Nils Abraham Langlet, who found helium emanating from the uranium ore cleveite. In 1903, large reserves of helium were found in gas fields in parts of the United States. Liquid helium is used in cryogenics, particularly in the cooling of superconducting magnets, a well-known but minor use is as a lifting gas in balloons and airships. As with any gas whose density differs from that of air, inhaling a small volume of helium temporarily changes the timbre, on Earth it is relatively rare—5.2 ppm by volume in the atmosphere. Most terrestrial helium present today is created by the radioactive decay of heavy radioactive elements. Previously, terrestrial helium—a non-renewable resource, because once released into the atmosphere it readily escapes into space—was thought to be in short supply. The first evidence of helium was observed on August 18,1868, the line was detected by French astronomer Jules Janssen during a total solar eclipse in Guntur, India. This line was assumed to be sodium. He concluded that it was caused by an element in the Sun unknown on Earth, Lockyer and English chemist Edward Frankland named the element with the Greek word for the Sun, ἥλιος
18.
Water
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Water is a transparent and nearly colorless chemical substance that is the main constituent of Earths streams, lakes, and oceans, and the fluids of most living organisms. Its chemical formula is H2O, meaning that its molecule contains one oxygen, Water strictly refers to the liquid state of that substance, that prevails at standard ambient temperature and pressure, but it often refers also to its solid state or its gaseous state. It also occurs in nature as snow, glaciers, ice packs and icebergs, clouds, fog, dew, aquifers, Water covers 71% of the Earths surface. It is vital for all forms of life. Only 2. 5% of this water is freshwater, and 98. 8% of that water is in ice and groundwater. Less than 0. 3% of all freshwater is in rivers, lakes, and the atmosphere, a greater quantity of water is found in the earths interior. Water on Earth moves continually through the cycle of evaporation and transpiration, condensation, precipitation. Evaporation and transpiration contribute to the precipitation over land, large amounts of water are also chemically combined or adsorbed in hydrated minerals. Safe drinking water is essential to humans and other even though it provides no calories or organic nutrients. There is a correlation between access to safe water and gross domestic product per capita. However, some observers have estimated that by 2025 more than half of the population will be facing water-based vulnerability. A report, issued in November 2009, suggests that by 2030, in developing regions of the world. Water plays an important role in the world economy, approximately 70% of the freshwater used by humans goes to agriculture. Fishing in salt and fresh water bodies is a source of food for many parts of the world. Much of long-distance trade of commodities and manufactured products is transported by boats through seas, rivers, lakes, large quantities of water, ice, and steam are used for cooling and heating, in industry and homes. Water is an excellent solvent for a variety of chemical substances, as such it is widely used in industrial processes. Water is also central to many sports and other forms of entertainment, such as swimming, pleasure boating, boat racing, surfing, sport fishing, Water is a liquid at the temperatures and pressures that are most adequate for life. Specifically, at atmospheric pressure of 1 bar, water is a liquid between the temperatures of 273.15 K and 373.15 K
19.
Brown dwarf
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Below this range are the sub-brown dwarfs, and above it are the lightest red dwarfs. Brown dwarfs may be fully convective, with no layers or chemical differentiation by depth, unlike the stars in the main-sequence, brown dwarfs are not massive enough to sustain nuclear fusion of ordinary hydrogen to helium in their cores. They are, however, thought to fuse deuterium and to fuse lithium if their mass is above a threshold of 13 MJ and 65 MJ. It is also debated whether brown dwarfs would be defined by their formation processes rather than by their supposed nuclear fusion reactions. Stars are categorized by spectral class, with brown dwarfs designated as types M, L, T, despite their name, brown dwarfs are of different colors. Many brown dwarfs would likely appear magenta to the human eye, Brown dwarfs are not very luminous at visible wavelengths. Planets are known to orbit some brown dwarfs, 2M1207b, MOA-2007-BLG-192Lb, at a distance of about 6.5 light years, the nearest known brown dwarf is Luhman 16, a binary system of brown dwarfs discovered in 2013. DENIS-P J082303. 1-491201 b is listed as the known exoplanet in NASAs exoplanet archive. However, a) the term black dwarf was already in use to refer to a white dwarf, b) red dwarfs fuse hydrogen. Because of this, alternate names for these objects were proposed, in 1975, Jill Tarter suggested the term brown dwarf, using brown as an approximate color. The term black dwarf still refers to a dwarf that has cooled to the point that it no longer emits significant light. The first self-consistent calculation of the minimum mass confirmed a value between 0.08 and 0.07 solar masses for population I objects. The discovery of deuterium burning down to 0.012 solar masses, however, such objects were hard to find as they emit almost no visible light. Their strongest emissions are in the spectrum, and ground-based IR detectors were too imprecise at that time to readily identify any brown dwarfs. Since then, numerous searches by various methods have sought these objects, for many years, efforts to discover brown dwarfs were fruitless. In 1988, however, a faint companion to a known as GD165 was found in an infrared search of white dwarfs. The spectrum of the companion GD 165B was very red and enigmatic and it became clear that GD 165B would need to be classified as a much cooler object than the latest M dwarfs then known. GD 165B remained unique for almost a decade until the advent of the Two Micron All Sky Survey which discovered many objects with similar colors, today, GD 165B is recognized as the prototype of a class of objects now called L dwarfs
20.
Nuclear fusion
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In nuclear physics, nuclear fusion is a reaction in which two or more atomic nuclei come close enough to form one or more different atomic nuclei and subatomic particles. The difference in mass between the products and reactants is manifested as the release of large amounts of energy and this difference in mass arises due to the difference in atomic binding energy between the atomic nuclei before and after the reaction. Fusion is the process that powers active or main sequence stars, the fusion process that produces a nucleus lighter than iron-56 or nickel-62 will generally yield a net energy release. These elements have the smallest mass per nucleon and the largest binding energy per nucleon, the opposite is true for the reverse process, nuclear fission. This means that the elements, such as hydrogen and helium, are in general more fusable, while the heavier elements. The extreme astrophysical event of a supernova can produce energy to fuse nuclei into elements heavier than iron. During the remainder of that decade the steps of the cycle of nuclear fusion in stars were worked out by Hans Bethe. Research into fusion for military purposes began in the early 1940s as part of the Manhattan Project, fusion was accomplished in 1951 with the Greenhouse Item nuclear test. Nuclear fusion on a scale in an explosion was first carried out on November 1,1952. Research into developing controlled thermonuclear fusion for civil purposes also began in earnest in the 1950s, the protons are positively charged and repel each other but they nonetheless stick together, demonstrating the existence of another force referred to as nuclear attraction. This force, called the nuclear force, overcomes electric repulsion at very close range. The effect of force is not observed outside the nucleus. The same force also pulls the nucleons together allowing ordinary matter to exist, light nuclei, are sufficiently small and proton-poor allowing the nuclear force to overcome the repulsive Coulomb force. This is because the nucleus is small that all nucleons feel the short-range attractive force at least as strongly as they feel the infinite-range Coulomb repulsion. Building up these nuclei from lighter nuclei by fusion thus releases the energy from the net attraction of these particles. For larger nuclei, however, no energy is released, since the force is short-range. Thus, energy is no longer released when such nuclei are made by fusion, instead, fusion reactions create the light elements that power the stars and produce virtually all elements in a process called nucleosynthesis. The fusion of elements in stars releases energy and the mass that always accompanies it
21.
James Blish
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James Benjamin Blish was an American author of fantasy and science fiction. Blish also wrote criticism of science fiction using the pen-name William Atheling, Jr. Blish was born at East Orange. In the late 1930s to the early 1940s, Blish was a member of the Futurians and he broke into science fiction print with two stories published by Frederik Pohl in Super Science Stories, Emergency Refueling in March and Bequest of the Angel in May 1940. ISFDB catalogs ten more stories published during 1941 and 1942, Blish trained as a biologist at Rutgers and Columbia University, and spent 1942–1944 as a medical technician in the United States Army. After the war he became the editor for the Pfizer pharmaceutical company. His writing career progressed until he gave up his job to become a professional writer and he is credited with coining the term gas giant, in the story Solar Plexus as it appeared in the anthology Beyond Human Ken, edited by Judith Merril. From 1962 to 1968, Blish worked for the Tobacco Institute, Blish adapted episodes of Star Trek for Bantam Books. They were collected into volumes, and published as a title series of the same name from 1967 to 1977. The adaptations were based on draft scripts, often containing additional plot elements or differing situations from the televised episodes. The original novel Spock Must Die. also by Blish, was released by Bantam in 1970, Blish noted his financial stability later in life was the result of his Star Trek work. Releases after Star Trek 6 were likely written in collaboration with his wife Judith Lawrence, Blish died before the series was completed, and the final volume, Star Trek 12, was co-credited to his wife. She continued the series with Mudds Angels in 1978, the archive of Blishs books and papers is deposited at the Bodleian Library in Oxford. Blish is buried in Holywell Cemetery, Oxford, perhaps Blishs most famous works were the Okies stories, known collectively as Cities in Flight, published in the science-fiction digest magazine Astounding Science Fiction. The framework for these was set in the first of four novels, They Shall Have Stars, the second is the development of an antigravity device known as the spindizzy. Since the device becomes more efficient when used to larger objects, entire cities leave an Earth in decline and rove the stars. The long life provided by ascomycin is necessary because the journeys between stars are time-consuming, the second, A Life For The Stars, is a coming of age story set amid flying cities. For his fourth and final installment, The Triumph of Time, a film version of Cities in Flight was in pre-production by Spacefilms in 1979, but never materialized. This term describes the background of a number of Blishs science fiction short stories, Three distinct technologies, their invention, and consequences are outlined
22.
Metallic hydrogen
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Metallic hydrogen is a kind of degenerate matter, a phase of hydrogen in which it behaves like an electrical conductor. This phase was predicted in 1935 on theoretical grounds by Eugene Wigner, in October 2016, there were claims that metallic hydrogen had been observed in the laboratory at a pressure of around 495 gigapascals. In January 2017, scientists at Harvard University reported the first creation of hydrogen in a laboratory. However, several researchers in the field doubt this claim, though often placed at the top of the alkali metal column in the periodic table, hydrogen does not, under ordinary conditions, exhibit the properties of an alkali metal. Instead, it forms diatomic H2 molecules, analogous to halogens and non-metals in the row of the periodic table. Diatomic hydrogen is a gas that, at pressure, liquefies and solidifies only at very low temperature. Since then, producing hydrogen in the laboratory has been described as. the holy grail of high-pressure physics. The initial prediction about the amount of pressure needed was eventually shown to be too low, helium-4 is a liquid at normal pressure near absolute zero, a consequence of its high zero-point energy. The ZPE of protons in a state is also high. In 1968, Neil Ashcroft suggested that metallic hydrogen might be a superconductor, up to room temperature and this hypothesis is based on an expected strong coupling between conduction electrons and lattice vibrations. Presently known super states of matter are superconductors, superfluid liquids and gases, egor Babaev predicted that if hydrogen and deuterium have liquid metallic states, they might have quantum ordered states that cannot be classified as superconducting or superfluid in the usual sense. Instead, they represent two possible novel types of quantum fluids, superconducting superfluids and metallic superfluids. Such fluids were predicted to have highly unusual reactions to external fields and rotations. It has also suggested that, under the influence of magnetic field, hydrogen might exhibit phase transitions from superconductivity to superfluidity. In 2009, Zurek et al.6 g/cm3, the team did not expect to produce metallic hydrogen, as it was not using solid hydrogen, thought to be necessary, and was working at temperatures above those specified by metallization theory. Previous studies in which hydrogen was compressed inside diamond anvils to pressures of up to 2500000 atm. The team had sought simply to measure the less extreme electrical conductivity changes they expected, the liquid hydrogen was in contact with wires leading to a device measuring electrical resistance. The scientists found that, as pressure rose to 1400000 atm, the energy band gap
23.
Mars
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Mars is the fourth planet from the Sun and the second-smallest planet in the Solar System, after Mercury. Named after the Roman god of war, it is referred to as the Red Planet because the iron oxide prevalent on its surface gives it a reddish appearance. Mars is a planet with a thin atmosphere, having surface features reminiscent both of the impact craters of the Moon and the valleys, deserts, and polar ice caps of Earth. The rotational period and seasonal cycles of Mars are likewise similar to those of Earth, Mars is the site of Olympus Mons, the largest volcano and second-highest known mountain in the Solar System, and of Valles Marineris, one of the largest canyons in the Solar System. The smooth Borealis basin in the northern hemisphere covers 40% of the planet, Mars has two moons, Phobos and Deimos, which are small and irregularly shaped. These may be captured asteroids, similar to 5261 Eureka, a Mars trojan, there are ongoing investigations assessing the past habitability potential of Mars, as well as the possibility of extant life. Future astrobiology missions are planned, including the Mars 2020 and ExoMars rovers, liquid water cannot exist on the surface of Mars due to low atmospheric pressure, which is about 6⁄1000 that of the Earths, except at the lowest elevations for short periods. The two polar ice caps appear to be largely of water. The volume of ice in the south polar ice cap, if melted. On November 22,2016, NASA reported finding a large amount of ice in the Utopia Planitia region of Mars. The volume of water detected has been estimated to be equivalent to the volume of water in Lake Superior, Mars can easily be seen from Earth with the naked eye, as can its reddish coloring. Its apparent magnitude reaches −2.91, which is surpassed only by Jupiter, Venus, the Moon, optical ground-based telescopes are typically limited to resolving features about 300 kilometers across when Earth and Mars are closest because of Earths atmosphere. Mars is approximately half the diameter of Earth with an area only slightly less than the total area of Earths dry land. Mars is less dense than Earth, having about 15% of Earths volume and 11% of Earths mass, the red-orange appearance of the Martian surface is caused by iron oxide, or rust. It can look like butterscotch, other common colors include golden, brown, tan. Like Earth, Mars has differentiated into a metallic core overlaid by less dense materials. Current models of its interior imply a core with a radius of about 1,794 ±65 kilometers, consisting primarily of iron and this iron sulfide core is thought to be twice as rich in lighter elements than Earths. The core is surrounded by a mantle that formed many of the tectonic and volcanic features on the planet
24.
Phase (matter)
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In the physical sciences, a phase is a region of space, throughout which all physical properties of a material are essentially uniform. Examples of physical properties include density, index of refraction, magnetization, a simple description is that a phase is a region of material that is chemically uniform, physically distinct, and mechanically separable. In a system consisting of ice and water in a jar, the ice cubes are one phase, the water is a second phase. The glass of the jar is another separate phase, the term phase is sometimes used as a synonym for state of matter, but there can be several immiscible phases of the same state of matter. Also, the phase is sometimes used to refer to a set of equilibrium states demarcated in terms of state variables such as pressure and temperature by a phase boundary on a phase diagram. Distinct phases may be described as different states of such as gas, liquid, solid. Useful mesophases between solid and liquid form other states of matter, distinct phases may also exist within a given state of matter. As shown in the diagram for iron alloys, several phases exist for both the solid and liquid states, phases may also be differentiated based on solubility as in polar or non-polar. A mixture of water and oil will separate into two phases. Water has a low solubility in oil, and oil has a low solubility in water. Solubility is the amount of a solute that can dissolve in a solvent before the solute ceases to dissolve. A mixture can separate into more than two phases and the concept of phase separation extends to solids, i. e. solids can form solid solutions or crystallize into distinct crystal phases. Metal pairs that are mutually soluble can form alloys, whereas metal pairs that are mutually insoluble cannot, as many as eight immiscible liquid phases have been observed. Mutually immiscible liquid phases are formed from water, hydrophobic solvents, perfluorocarbons, silicones, several different metals. Not all organic solvents are completely miscible, e. g. a mixture of ethylene glycol, phases do not need to macroscopically separate spontaneously. Emulsions and colloids are examples of immiscible phase pair combinations that do not physically separate, left to equilibration, many compositions will form a uniform single phase, but depending on the temperature and pressure even a single substance may separate into two or more distinct phases. Within each phase, the properties are uniform but between the two phases properties differ, water in a closed jar with an air space over it forms a two phase system. Most of the water is in the phase, where it is held by the mutual attraction of water molecules
25.
Oxygen
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Oxygen is a chemical element with symbol O and atomic number 8. It is a member of the group on the periodic table and is a highly reactive nonmetal. By mass, oxygen is the third-most abundant element in the universe, after hydrogen, at standard temperature and pressure, two atoms of the element bind to form dioxygen, a colorless and odorless diatomic gas with the formula O2. This is an important part of the atmosphere and diatomic oxygen gas constitutes 20. 8% of the Earths atmosphere, additionally, as oxides the element makes up almost half of the Earths crust. Most of the mass of living organisms is oxygen as a component of water, conversely, oxygen is continuously replenished by photosynthesis, which uses the energy of sunlight to produce oxygen from water and carbon dioxide. Oxygen is too reactive to remain a free element in air without being continuously replenished by the photosynthetic action of living organisms. Another form of oxygen, ozone, strongly absorbs ultraviolet UVB radiation, but ozone is a pollutant near the surface where it is a by-product of smog. At low earth orbit altitudes, sufficient atomic oxygen is present to cause corrosion of spacecraft, the name oxygen was coined in 1777 by Antoine Lavoisier, whose experiments with oxygen helped to discredit the then-popular phlogiston theory of combustion and corrosion. One of the first known experiments on the relationship between combustion and air was conducted by the 2nd century BCE Greek writer on mechanics, Philo of Byzantium. In his work Pneumatica, Philo observed that inverting a vessel over a burning candle, Philo incorrectly surmised that parts of the air in the vessel were converted into the classical element fire and thus were able to escape through pores in the glass. Many centuries later Leonardo da Vinci built on Philos work by observing that a portion of air is consumed during combustion and respiration, Oxygen was discovered by the Polish alchemist Sendivogius, who considered it the philosophers stone. In the late 17th century, Robert Boyle proved that air is necessary for combustion, English chemist John Mayow refined this work by showing that fire requires only a part of air that he called spiritus nitroaereus. From this he surmised that nitroaereus is consumed in both respiration and combustion, Mayow observed that antimony increased in weight when heated, and inferred that the nitroaereus must have combined with it. Accounts of these and other experiments and ideas were published in 1668 in his work Tractatus duo in the tract De respiratione. Robert Hooke, Ole Borch, Mikhail Lomonosov, and Pierre Bayen all produced oxygen in experiments in the 17th and the 18th century but none of them recognized it as a chemical element. This may have been in part due to the prevalence of the philosophy of combustion and corrosion called the phlogiston theory, which was then the favored explanation of those processes. Established in 1667 by the German alchemist J. J. Becher, one part, called phlogiston, was given off when the substance containing it was burned, while the dephlogisticated part was thought to be its true form, or calx. The fact that a substance like wood gains overall weight in burning was hidden by the buoyancy of the combustion products
26.
Carbon
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Carbon is a chemical element with symbol C and atomic number 6. It is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds, three isotopes occur naturally, 12C and 13C being stable, while 14C is a radioactive isotope, decaying with a half-life of about 5,730 years. Carbon is one of the few elements known since antiquity, Carbon is the 15th most abundant element in the Earths crust, and the fourth most abundant element in the universe by mass after hydrogen, helium, and oxygen. It is the second most abundant element in the body by mass after oxygen. The atoms of carbon can bond together in different ways, termed allotropes of carbon, the best known are graphite, diamond, and amorphous carbon. The physical properties of carbon vary widely with the allotropic form, for example, graphite is opaque and black while diamond is highly transparent. Graphite is soft enough to form a streak on paper, while diamond is the hardest naturally occurring material known, graphite is a good electrical conductor while diamond has a low electrical conductivity. Under normal conditions, diamond, carbon nanotubes, and graphene have the highest thermal conductivities of all known materials, all carbon allotropes are solids under normal conditions, with graphite being the most thermodynamically stable form. They are chemically resistant and require high temperature to react even with oxygen, the most common oxidation state of carbon in inorganic compounds is +4, while +2 is found in carbon monoxide and transition metal carbonyl complexes. The largest sources of carbon are limestones, dolomites and carbon dioxide, but significant quantities occur in organic deposits of coal, peat, oil. For this reason, carbon has often referred to as the king of the elements. The allotropes of carbon graphite, one of the softest known substances, and diamond. It bonds readily with other small atoms including other carbon atoms, Carbon is known to form almost ten million different compounds, a large majority of all chemical compounds. Carbon also has the highest sublimation point of all elements, although thermodynamically prone to oxidation, carbon resists oxidation more effectively than elements such as iron and copper that are weaker reducing agents at room temperature. Carbon is the element, with a ground-state electron configuration of 1s22s22p2. Its first four ionisation energies,1086.5,2352.6,4620.5 and 6222.7 kJ/mol, are higher than those of the heavier group 14 elements. Carbons covalent radii are normally taken as 77.2 pm,66.7 pm and 60.3 pm, although these may vary depending on coordination number, in general, covalent radius decreases with lower coordination number and higher bond order. Carbon compounds form the basis of all life on Earth
27.
Silicon
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Silicon is a chemical element with symbol Si and atomic number 14. A hard and brittle crystalline solid with a metallic luster. It is a member of group 14 in the table, along with carbon above it and germanium, tin, lead. It is not very reactive, although more reactive than germanium, Silicon is the eighth most common element in the universe by mass, but very rarely occurs as the pure element in the Earths crust. It is most widely distributed in dusts, sands, planetoids, over 90% of the Earths crust is composed of silicate minerals, making silicon the second most abundant element in the Earths crust after oxygen. Most silicon is used commercially without being separated, and often with little processing of the natural minerals, such use includes industrial construction with clays, silica sand, and stone. Silicate is used in Portland cement for mortar and stucco, and mixed with sand and gravel to make concrete for walkways, foundations. Silicates are used in whiteware ceramics such as porcelain, and in traditional quartz-based soda-lime glass, Silicon compounds such as silicon carbide are used as abrasives and components of high-strength ceramics. Elemental silicon also has an impact on the modern world economy. Most free silicon is used in the refining, aluminium-casting. Silicon is the basis of the widely used synthetic polymers called silicones, Silicon is an essential element in biology, although only tiny traces are required by animals. However, various sea sponges and microorganisms, such as diatoms and radiolaria, silica is deposited in many plant tissues, such as in the bark and wood of Chrysobalanaceae and the silica cells and silicified trichomes of Cannabis sativa, horsetails and many grasses. Silicon is a solid at room temperature, with a point of 1,414 °C. Like water, it has a density in a liquid state than in a solid state and it expands when it freezes. With a relatively high conductivity of 149 W·m−1·K−1, silicon conducts heat well. In its crystalline form, pure silicon has a gray color, like germanium, silicon is rather strong, very brittle, and prone to chipping. Silicon, like carbon and germanium, crystallizes in a cubic crystal structure with a lattice spacing of 0.5430710 nm. The outer electron orbital of silicon, like that of carbon, has four valence electrons, the 1s, 2s, 2p and 3s subshells are completely filled while the 3p subshell contains two electrons out of a possible six
28.
Jupiter (mythology)
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Jupiter, also Jove, is the god of sky and thunder and king of the gods in Ancient Roman religion and mythology. Jupiter was the deity of Roman state religion throughout the Republican and Imperial eras. In Roman mythology, he negotiates with Numa Pompilius, the king of Rome, to establish principles of Roman religion such as offering. Jupiter is usually thought to have originated as a sky god, the two emblems were often combined to represent the god in the form of an eagle holding in its claws a thunderbolt, frequently seen on Greek and Roman coins. As the sky-god, he was a witness to oaths. Many of his functions were focused on the Capitoline Hill, where the citadel was located and he was the chief deity of the early Capitoline Triad with Mars and Quirinus. In the later Capitoline Triad, he was the guardian of the state with Juno. His sacred tree was the oak, the Romans regarded Jupiter as the equivalent of the Greek Zeus, and in Latin literature and Roman art, the myths and iconography of Zeus are adapted under the name Iuppiter. In the Greek-influenced tradition, Jupiter was the brother of Neptune, each presided over one of the three realms of the universe, sky, the waters, and the underworld. The Italic Diespiter was also a sky god who manifested himself in the daylight, usually, Tinia is usually regarded as his Etruscan counterpart. The Romans believed that Jupiter granted them supremacy because they had honoured him more than any other people had, Jupiter was the fount of the auspices upon which the relationship of the city with the gods rested. He personified the divine authority of Romes highest offices, internal organization and his image in the Republican and Imperial Capitol bore regalia associated with Romes ancient kings and the highest consular and Imperial honours. The consuls swore their oath of office in Jupiters name, to thank him for his help, they offered him a white ox with gilded horns. A similar offering was made by generals, who surrendered the tokens of their victory at the feet of Jupiters statue in the Capitol. Some scholars have viewed the triumphator as embodying Jupiter in the triumphal procession, Jupiters association with kingship and sovereignty was reinterpreted as Romes form of government changed. Originally, Rome was ruled by kings, after the monarchy was abolished and the Republic established, religious prerogatives were transferred to the patres, nostalgia for the kingship was considered treasonous. Those suspected of harbouring monarchical ambitions were punished, regardless of their service to the state, in the 5th century BC, the triumphator Camillus was sent into exile after he drove a chariot with a team of four white horses —an honour reserved for Jupiter himself. His house on the Capitoline Hill was razed, and it was decreed that no patrician should ever be allowed to live there, during the Conflict of the Orders, Romes plebeians demanded the right to hold political and religious office
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Deuterium
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Deuterium is one of two stable isotopes of hydrogen. The nucleus of deuterium, called a deuteron, contains one proton and one neutron, whereas the far more common hydrogen isotope, Deuterium has a natural abundance in Earths oceans of about one atom in 6420 of hydrogen. Thus deuterium accounts for approximately 0. 0156% of all the naturally occurring hydrogen in the oceans, the abundance of deuterium changes slightly from one kind of natural water to another. The deuterium isotopes name is formed from the Greek deuteros meaning second, Deuterium was discovered and named in 1931 by Harold Urey. When the neutron was discovered in 1932, this made the structure of deuterium obvious. Soon after deuteriums discovery, Urey and others produced samples of water in which the deuterium content had been highly concentrated. Deuterium is destroyed in the interiors of stars faster than it is produced, other natural processes are thought to produce only an insignificant amount of deuterium. Nearly all deuterium found in nature was produced in the Big Bang 13.8 billion years ago and this is the ratio found in the gas giant planets, such as Jupiter. However, other bodies are found to have different ratios of deuterium to hydrogen-1. This is thought to be as a result of natural isotope separation processes that occur from solar heating of ices in comets, like the water-cycle in Earths weather, such heating processes may enrich deuterium with respect to protium. The analysis of ratios in comets found results very similar to the mean ratio in Earths oceans. This reinforces theories that much of Earths ocean water is of cometary origin, the deuterium/protium ratio of the comet 67P/Churyumov-Gerasimenko, as measured by the Rosetta space probe, is about three times that of earth water. This figure is the highest yet measured in a comet, deuterium/protium ratios thus continue to be an active topic of research in both astronomy and climatology. Deuterium is frequently represented by the chemical symbol D, since it is an isotope of hydrogen with mass number 2, it is also represented by 2H. IUPAC allows both D and 2H, although 2H is preferred, a distinct chemical symbol is used for convenience because of the isotopes common use in various scientific processes. In quantum mechanics the energy levels of electrons in atoms depend on the mass of the system of electron. For hydrogen, this amount is about 1837/1836, or 1.000545, the energies of spectroscopic lines for deuterium and light-hydrogen therefore differ by the ratios of these two numbers, which is 1.000272. The wavelengths of all deuterium spectroscopic lines are shorter than the lines of light hydrogen
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Jupiter mass
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Jupiter mass is the unit of mass equal to the total mass of the planet Jupiter. Jupiter mass is used to describe masses of the gas giants, such as the outer planets and it is also used in describing brown dwarfs. The most massive exoplanets are typically described in terms of Jupiter masses as this provides a convenient scale for comparison, a Jupiter-mass planet at an orbital distance of 1 AU from a Sun-like star causes an amplitude shift of 28 m/s, which is detectable with current technology. The most readily detectable planets through radial velocity measurements have high mass and this produces a selection effect for planets of Jupiter mass. Likewise, Jupiter mass or higher planets are likely to be detected through other means. A planet with a Jupiter mass might not have the same dimensions, in the Solar System, the masses of the outer planets can be listed in Jupiter mass. The other gas giants are far less massive than Jupiter
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Hot Jupiter
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Hot Jupiters are a class of exoplanets that are inferred to be physically similar to Jupiter but that have very short orbital radii with semi-major axes from 0.015 to 0.05 astronomical units. The close proximity to their stars and high temperatures resulted in the moniker hot Jupiters. One of the best-known hot Jupiters is 51 Pegasi b, discovered in 1995, it was the first extrasolar planet found orbiting a Sun-like star. 51 Pegasi b has a period of about 4 days. Though there is diversity among hot Jupiters, they do share common properties. Their defining characteristics are their large masses and short orbital periods, the mass cannot be greater than approximately 13.6 Jupiter masses because then the planet would start burning deuterium and become a brown dwarf. It is thought that their orbits are circularized by perturbations from nearby stars or tidal forces, the lowest one measured thus far is that of TrES-4 at 0.222 g/cm3. They are likely to have extreme and exotic atmospheres due to their periods, relatively long days. Atmospheric dynamics models predict strong vertical stratification with intense winds and super-rotating equatorial jets driven by radiative forcing, the day-night temperature difference at the photosphere is predicted to be substantial, approximately 500 K for a model based on HD 209458b. They appear to be common around F- and G-type stars. Hot Jupiters around red dwarfs are very rare, generalizations about the distribution of these planets must take into account the various observational biases. In the migration hypothesis, hot Jupiters are thought to form at a distance from the star beyond the frost line, the planets then migrate inwards to the star where they eventually form a stable orbit. The planets usually move by type II orbital migration, or possibly via interaction with other planets or a stellar companion and it has been shown that approximately 50% of hot Jupiters have distant Jupiter-mass or larger companions. The migration happens during the solar nebula phase, i. e. when gas is still present, energetic stellar photons and strong stellar winds at this time remove most of the remaining nebula. If their atmospheres are stripped away via hydrodynamic escape, their cores may become chthonian planets, the amount of gas removed from the outermost layers depends on the planet size, the envelope gases, the orbital distance from the star, and on the stellar luminosity. It should be noted none of such objects have been found yet. It is also theorized that a fraction of hot Jupiters may have formed in-situ via the core accretion method of planetary formation. Recent surveys, however, have found that the regions of planetary systems are not empty
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Nice model
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The Nice model is a scenario for the dynamical evolution of the Solar System. It is named for the location of the Observatoire de la Côte dAzur and it proposes the migration of the giant planets from an initial compact configuration into their present positions, long after the dissipation of the initial protoplanetary gas disk. In this way, it differs from earlier models of the Solar Systems formation.5 and ~17 astronomical units, much more closely spaced and compact than in the present. A large, dense disk of small, rock and ice planetesimals, their total about 35 Earth masses, scientists understand so little about the formation of Uranus and Neptune that Levison states. the possibilities concerning the formation of Uranus and Neptune are almost endless. However, it is suggested that this system evolved in the following manner. Planetesimals at the inner edge occasionally pass through gravitational encounters with the outermost giant planet. These planetesimals then similarly scatter off the planet they encounter, successively moving the orbits of Uranus, Neptune. Despite the minute movement each exchange of momentum can produce, cumulatively these planetesimal encounters shift the orbits of the planets by significant amounts and this, in contrast, causes Jupiter to move slightly inward. The low rate of orbital encounters governs the rate at which planetesimals are lost from the disk, after several hundreds of millions of years of slow, gradual migration, Jupiter and Saturn, the two inmost giant planets, cross their mutual 1,2 mean-motion resonance. This resonance increases their eccentricities, destabilizing the entire planetary system. The arrangement of the giant planets alters quickly and dramatically and these ice giants then plough into the planetesimal disk, scattering tens of thousands of planetesimals from their formerly stable orbits in the outer Solar System. This disruption almost entirely scatters the primordial disk, removing 99% of its mass, some of the planetesimals are thrown into the inner Solar System, producing a sudden influx of impacts on the terrestrial planets, the Late Heavy Bombardment. In some 50% of the models of Tsiganis and colleagues, Neptune. As the initial conditions of the model are allowed to vary, each population will be more or less numerous, proving a model of the evolution of the early Solar System is difficult, since the evolution cannot be directly observed. However, the success of any dynamical model can be judged by comparing the population predictions from the simulations to astronomical observations of these populations. At the present time, computer models of the Solar System that are begun with the conditions of the Nice scenario best match many aspects of the observed Solar System. In the Nice model icy planetesimals are scattered onto planet-crossing orbits when the disc is disrupted by Uranus. The migration of outer planets also causes mean-motion and secular resonances to sweep through the inner Solar System, the number of planetesimals that would reach the Moon is consistent with the crater record from the LHB
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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
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O-type main-sequence star
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An O-type main-sequence star is a main-sequence star of spectral type O and luminosity class V. These stars have between 15 and 90 times the mass of the Sun and surface temperatures between 30,000 and 52,000 K and they are between 30,000 and 1,000,000 times as luminous as the Sun. These stars are rare, it is estimated there are no more than 20,000 in the entire Milky Way. Examples include σ Orionis A and 10 Lacertae, the Morgan–Keenan–Kellerman Yerkes atlas from 1943 listed O-type standards between O5 and O9, but only split luminosity classes for the O9s. The two MKK O9 V standards were Iota Orionis and 10 Lacertae, the revised Yerkes standards presented listed in Johnson & Morgan presented no changes to the O5 to O8 types, and listed 5 O9 V standards and 3 O9.5 V standards. An important review on spectral classification by Morgan & Keenan listed revised MK standards for O4 to O7 and this review also listed main-sequence dagger standards of O9 V for 10 Lacertae and O9.5 V for Sigma Orionis. O-type luminosity classes for subtypes earlier than O5 were not defined with standard stars until the 1970s. The spectral atlas of Morgan, Abt, & Tapscott defined listed several O-type main-sequence standards, HD46223, HD46150, HD199579, HD47839, HD46149, and HD46202. Walborn & Fitzpartrick provided the first digital atlas of spectra for OB-type stars, spectral class O2 was defined in Walborn et al. with the star BI253 acting as the O2 V primary standard. They also redefined HDE303308 as an O4 V standard, the effective temperatures of O3 V stars are likely near 50,000 Kelvin. O-type star Star count, survey of stars Stellar classification
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Protoplanetary disk
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A protoplanetary disk is a rotating circumstellar disk of dense gas and dust surrounding a young newly formed star, a T Tauri star, or Herbig Ae/Be star. The protoplanetary disk may also be considered an accretion disk for the star itself, but this process should not be confused with the accretion process thought to build up the planets themselves. Externally illuminated photo-evaporating protoplanetary disks are called proplyds, protostars mainly form from molecular clouds consisting primarily of molecular hydrogen. When a portion of a cloud reaches a critical size, mass, or density. As this collapsing cloud, called a solar nebula, becomes denser, conservation of angular momentum causes the rotation to increase as the nebula radius decreases. This rotation causes the cloud to flatten out—much like forming a flat pizza out of dough—and take the form of a disk, the initial collapse takes about 100,000 years. After that time the star reaches a temperature similar to that of a main sequence star of the same mass. It is now a T Tauri star, the oldest protoplanetary disk yet discovered is 25 million years old. Protoplanetary disks around T Tauri stars differ from the surrounding the primary components of close binary systems with respect to their size. Protoplanetary disks have radii up to 1000 AU, and only their innermost parts reach temperatures above 1000 K and they are very often accompanied by jets. Protoplanetary disks have been observed around several stars in our galaxy. Recent observations by the Hubble Space Telescope have shown proplyds and planetary disks to be forming within the Orion Nebula. Protoplanetary disks are thought to be structures, with a typical vertical height much smaller than the radius. The mass of a typical disk is dominated by its gas, however. Dust grains shield the mid-plane of the disk from energetic radiation from space that creates a dead zone in which the MRI no longer operates. It is believed that these disks consist of a turbulent envelope of plasma, also called the active zone, the dead zone located at the mid-plane can slow down the flow of matter through the disk which prohibits achieving a steady state. The nebular hypothesis of solar system formation describes how protoplanetary disks are thought to evolve into planetary systems, electrostatic and gravitational interactions may cause the dust and ice grains in the disk to accrete into planetesimals. This process competes against the wind, which drives the gas out of the system, and gravity
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Ultraviolet
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Ultraviolet is an electromagnetic radiation with a wavelength from 10 nm to 400 nm, shorter than that of visible light but longer than X-rays. UV radiation constitutes about 10% of the light output of the Sun. It is also produced by electric arcs and specialized lights, such as lamps, tanning lamps. Consequently, the effects of UV are greater than simple heating effects. Suntan, freckling and sunburn are familiar effects of over-exposure, along with risk of skin cancer. Living things on dry land would be damaged by ultraviolet radiation from the Sun if most of it were not filtered out by the Earths atmosphere. More-energetic, shorter-wavelength extreme UV below 121 nm ionizes air so strongly that it is absorbed before it reaches the ground, Ultraviolet is also responsible for the formation of bone-strengthening vitamin D in most land vertebrates, including humans. The UV spectrum thus has both beneficial and harmful to human health. Ultraviolet rays are invisible to most humans, the lens in a human eye ordinarily filters out UVB frequencies or higher, and humans lack color receptor adaptations for ultraviolet rays. Under some conditions, children and young adults can see ultraviolet down to wavelengths of about 310 nm, near-UV radiation is visible to some insects, mammals, and birds. Small birds have a fourth color receptor for ultraviolet rays, this gives birds true UV vision, reindeer use near-UV radiation to see polar bears, who are poorly visible in regular light because they blend in with the snow. UV also allows mammals to see urine trails, which is helpful for animals to find food in the wild. The males and females of some species look identical to the human eye. Ultraviolet means beyond violet, violet being the color of the highest frequencies of visible light, Ultraviolet has a higher frequency than violet light. He called them oxidizing rays to emphasize chemical reactivity and to them from heat rays. The terms chemical and heat rays were eventually dropped in favour of ultraviolet and infrared radiation, in 1878 the effect of short-wavelength light on sterilizing bacteria was discovered. By 1903 it was known the most effective wavelengths were around 250 nm, in 1960, the effect of ultraviolet radiation on DNA was established. The discovery of the ultraviolet radiation below 200 nm, named vacuum ultraviolet because it is absorbed by air, was made in 1893 by the German physicist Victor Schumann
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Stellar wind
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A stellar wind is a flow of gas ejected from the upper atmosphere of a star. It is distinguished from the bipolar outflows characteristic of stars by being less collimated. Different types of stars have different types of stellar winds, post-main-sequence stars nearing the ends of their lives often eject large quantities of mass in massive, slow winds. These include red giants and supergiants, and asymptotic giant branch stars and these winds are understood to be driven by radiation pressure on dust condensing in the upper atmosphere of the stars. Massive stars of types O and B have stellar winds with lower mass loss rates, such winds are driven by radiation pressure on the resonance absorption lines of heavy elements such as carbon and nitrogen. These high-energy stellar winds blow stellar wind bubbles, g-type stars like the Earths Sun have a wind driven by their hot, magnetized corona. The Suns wind is called the solar wind and these winds consist mostly of high-energy electrons and protons that are able to escape the stars gravity because of the high temperature of the corona. Stellar winds from main-sequence stars do not strongly influence the evolution of lower mass stars such as the Sun, solar wind Cosmic ray Cosmic wind
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Photoevaporation
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Photoevaporation denotes the process where energetic radiation ionises gas and causes it to disperse away from the ionising source. This typically refers to a context where ultraviolet radiation from hot stars acts on clouds of material such as molecular clouds, protoplanetary disks. One of the most obvious manifestations of astrophysical photoevaporation is seen in the structures of molecular clouds as luminous stars are born within. A planet can be stripped of its due to high energy photons. If a photon interacts with a molecule, the molecule is accelerated. If sufficient energy is provided, the molecule or atom may reach the velocity of the planet. The lower the number of the gas, the higher the velocity obtained by interaction with a photon. Thus hydrogen is the gas which is most prone to photoevaporation, protoplanetary disks can be dispersed by stellar wind and heating due to incident electromagnetic radiation. The radiation interacts with matter and thus accelerates it outwards and this effect is only noticeable when there is sufficient radiation strength, such as coming from nearby O and B type stars or when the central protostar commences nuclear fusion. The disk is composed of gas and dust, the gas, consisting mostly of light elements such as hydrogen and helium, is mainly affected by the effect, causing the ratio between dust and gas to increase. Radiation from the central star excites particles in the accretion disk, the irradiation of the disk gives rise to a stability length scale known as the gravitational radius. Outside of the radius, particles can become sufficiently excited to escape the gravity of the disk. After 106 –107 years, the accretion rates fall below the photoevaporation rates at r g. A gap then opens around r g, the inner disk drains onto the star, or spreads to r g. An inner hole extending to r g is produced, once an inner hole forms, the outer disk is very rapidly cleared. The formula for the radius of the disk is r g =2 γ G M μ k B T ≈1
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International Astronomical Union
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The International Astronomical Union is an international association of professional astronomers, at the PhD level and beyond, active in professional research and education in astronomy. Among other activities, it acts as the recognized authority for assigning designations to celestial bodies. The IAU is a member of the International Council for Science and its main objective is to promote and safeguard the science of astronomy in all its aspects through international cooperation. The IAU maintains friendly relations with organizations that include amateur astronomers in their membership, the IAU has its head office on the second floor of the Institut dAstrophysique de Paris in the 14th arrondissement of Paris. The IAU is also responsible for the system of astronomical telegrams which are produced and distributed on its behalf by the Central Bureau for Astronomical Telegrams, the Minor Planet Center also operates under the IAU, and is a clearinghouse for all non-planetary or non-moon bodies in the Solar System. The Working Group for Meteor Shower Nomenclature and the Meteor Data Center coordinate the nomenclature of meteor showers, the IAU was founded on July 28,1919, at the Constitutive Assembly of the International Research Council held in Brussels, Belgium. The 7 initial member states were Belgium, Canada, France, Great Britain, Greece, Japan, the first executive committee consisted of Benjamin Baillaud, Alfred Fowler, and four vice presidents, William Campbell, Frank Dyson, Georges Lecointe, and Annibale Riccò. Thirty-two Commissions were appointed at the Brussels meeting and focused on topics ranging from relativity to minor planets, the reports of these 32 Commissions formed the main substance of the first General Assembly, which took place in Rome, Italy, May 2–10,1922. By the end of the first General Assembly, ten nations had joined the Union. Although the Union was officially formed eight months after the end of World War I, the first 50 years of the Unions history are well documented. Subsequent history is recorded in the form of reminiscences of past IAU Presidents, twelve of the fourteen past General Secretaries in the period 1964-2006 contributed their recollections of the Unions history in IAU Information Bulletin No.100. Six past IAU Presidents in the period 1976–2003 also contributed their recollections in IAU Information Bulletin No.104, the IAU includes a total of 12,664 individual members who are professional astronomers from 96 countries worldwide. 83% of all members are male, while 17% are female, among them the unions current president. Membership also includes 79 national members, professional astronomical communities representing their countrys affiliation with the IAU, the sovereign body of the IAU is its General Assembly, which comprises all members. The Assembly determines IAU policy, approves the Statutes and By-Laws of the Union, the right to vote on matters brought before the Assembly varies according to the type of business under discussion. On budget matters, votes are weighted according to the subscription levels of the national members. A second category vote requires a turnout of at least two-thirds of national members in order to be valid, an absolute majority is sufficient for approval in any vote, except for Statute revision which requires a two-thirds majority. An equality of votes is resolved by the vote of the President of the Union, since 1922, the IAU General Assembly meets every three years, with the exception of the period between 1938 and 1948, due to World War II
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Super-Jupiter
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A super-Jupiter is an astronomical object that is more massive than the planet Jupiter. For example, companions at the planet–brown dwarf borderline have been called super-Jupiters, by 2011 there were 180 known super-Jupiters, some hot, some cold. Even though they are more massive than Jupiter, they remain about the size as Jupiter up to 80 Jupiter masses. This means that their surface gravity and density goes up proportionally with their mass, the increased mass compresses the planet due to gravity, thus keeping it from being larger. In comparison, somewhat lighter planets than Jupiter can be larger, an example of this may be the exoplanet HAT-P-1b with about half the mass of Jupiter but about 1.38 times larger diameter. Corot-3b, with a mass around 22 Jupiter masses, is predicted to have a density of 26.4 g/cm3, greater than osmium. Extreme compression of matter inside it causes the density, because it is likely composed mainly of hydrogen. The surface gravity is high, over 50 times that of Earth. In 2012, the super-Jupiter Kappa Andromedae b was imaged around the star Kappa Andromedae, ice giant Super-Earth Extrasolar planet Red dwarf List of planet types Brown dwarfs, Failed stars, super Jupiters
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