1.
Astronomy
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Astronomy is a natural science that studies celestial objects and phenomena. It applies mathematics, physics, and chemistry, in an effort to explain the origin of those objects and phenomena and their evolution. Objects of interest include planets, moons, stars, galaxies, and comets, while the phenomena include supernovae explosions, gamma ray bursts, more generally, all astronomical phenomena that originate outside Earths atmosphere are within the purview of astronomy. A related but distinct subject, physical cosmology, is concerned with the study of the Universe as a whole, Astronomy is the oldest of the natural sciences. The early civilizations in recorded history, such as the Babylonians, Greeks, Indians, Egyptians, Nubians, Iranians, Chinese, during the 20th century, the field of professional astronomy split into observational and theoretical branches. Observational astronomy is focused on acquiring data from observations of astronomical objects, theoretical astronomy is oriented toward the development of computer or analytical models to describe astronomical objects and phenomena. The two fields complement each other, with theoretical astronomy seeking to explain the results and observations being used to confirm theoretical results. Astronomy is one of the few sciences where amateurs can play an active role, especially in the discovery. Amateur astronomers have made and contributed to many important astronomical discoveries, Astronomy means law of the stars. Astronomy should not be confused with astrology, the system which claims that human affairs are correlated with the positions of celestial objects. Although the two share a common origin, they are now entirely distinct. Generally, either the term astronomy or astrophysics may be used to refer to this subject, however, since most modern astronomical research deals with subjects related to physics, modern astronomy could actually be called astrophysics. Few fields, such as astrometry, are purely astronomy rather than also astrophysics, some titles of the leading scientific journals in this field includeThe Astronomical Journal, The Astrophysical Journal and Astronomy and Astrophysics. In early times, astronomy only comprised the observation and predictions of the motions of objects visible to the naked eye, in some locations, early cultures assembled massive artifacts that possibly had some astronomical purpose. Before tools such as the telescope were invented, early study of the stars was conducted using the naked eye, most of early astronomy actually consisted of mapping the positions of the stars and planets, a science now referred to as astrometry. From these observations, early ideas about the motions of the planets were formed, and the nature of the Sun, Moon, the Earth was believed to be the center of the Universe with the Sun, the Moon and the stars rotating around it. This is known as the model of the Universe, or the Ptolemaic system. The Babylonians discovered that lunar eclipses recurred in a cycle known as a saros
2.
Natural satellite
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A natural satellite or moon is, in the most common usage, an astronomical body that orbits a planet or minor planet. In the Solar System there are six planetary satellite systems containing 178 known natural satellites, four IAU-listed dwarf planets are also known to have natural satellites, Pluto, Haumea, Makemake, and Eris. As of January 2012, over 200 minor-planet moons have been discovered, the Earth–Moon system is unique in that the ratio of the mass of the Moon to the mass of Earth is much greater than that of any other natural-satellite–planet ratio in the Solar System. At 3,474 km across, Earths Moon is 0.27 times the diameter of Earth, the first known natural satellite was the Moon, but it was considered a planet until Copernicus introduction of heliocentrism in 1543. Until the discovery of the Galilean satellites in 1610, however, galileo chose to refer to his discoveries as Planetæ, but later discoverers chose other terms to distinguish them from the objects they orbited. The first to use of the satellite to describe orbiting bodies was the German astronomer Johannes Kepler in his pamphlet Narratio de Observatis a se quatuor Iouis satellitibus erronibus in 1610. He derived the term from the Latin word satelles, meaning guard, attendant, or companion, the term satellite thus became the normal one for referring to an object orbiting a planet, as it avoided the ambiguity of moon. In 1957, however, the launching of the artificial object Sputnik created a need for new terminology, to further avoid ambiguity, the convention is to capitalize the word Moon when referring to Earths natural satellite, but not when referring to other natural satellites. A few recent authors define moon as a satellite of a planet or minor planet, there is no established lower limit on what is considered a moon. Small asteroid moons, such as Dactyl, have also been called moonlets, the upper limit is also vague. Two orbiting bodies are described as a double body rather than primary. Asteroids such as 90 Antiope are considered double asteroids, but they have not forced a clear definition of what constitutes a moon, some authors consider the Pluto–Charon system to be a double planet. In contrast, irregular satellites are thought to be captured asteroids possibly further fragmented by collisions, most of the major natural satellites of the Solar System have regular orbits, while most of the small natural satellites have irregular orbits. The Moon and possibly Charon are exceptions among large bodies in that they are thought to have originated by the collision of two large proto-planetary objects. The material that would have placed in orbit around the central body is predicted to have reaccreted to form one or more orbiting natural satellites. As opposed to planetary-sized bodies, asteroid moons are thought to form by this process. Triton is another exception, although large and in a close, circular orbit, its motion is retrograde, most regular moons in the Solar System are tidally locked to their respective primaries, meaning that the same side of the natural satellite always faces its planet. The only known exception is Saturns natural satellite Hyperion, which rotates chaotically because of the influence of Titan
3.
Moon
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The Moon is an astronomical body that orbits planet Earth, being Earths only permanent natural satellite. It is the fifth-largest natural satellite in the Solar System, following Jupiters satellite Io, the Moon is second-densest satellite among those whose densities are known. The average distance of the Moon from the Earth is 384,400 km, the Moon is thought to have formed about 4.51 billion years ago, not long after Earth. It is the second-brightest regularly visible celestial object in Earths sky, after the Sun and its surface is actually dark, although compared to the night sky it appears very bright, with a reflectance just slightly higher than that of worn asphalt. Its prominence in the sky and its cycle of phases have made the Moon an important cultural influence since ancient times on language, calendars, art. The Moons gravitational influence produces the ocean tides, body tides, and this matching of apparent visual size will not continue in the far future. The Moons linear distance from Earth is currently increasing at a rate of 3.82 ±0.07 centimetres per year, since the Apollo 17 mission in 1972, the Moon has been visited only by uncrewed spacecraft. The usual English proper name for Earths natural satellite is the Moon, the noun moon is derived from moone, which developed from mone, which is derived from Old English mōna, which ultimately stems from Proto-Germanic *mǣnōn, like all Germanic language cognates. Occasionally, the name Luna is used, in literature, especially science fiction, Luna is used to distinguish it from other moons, while in poetry, the name has been used to denote personification of our moon. The principal modern English adjective pertaining to the Moon is lunar, a less common adjective is selenic, derived from the Ancient Greek Selene, from which is derived the prefix seleno-. Both the Greek Selene and the Roman goddess Diana were alternatively called Cynthia, the names Luna, Cynthia, and Selene are reflected in terminology for lunar orbits in words such as apolune, pericynthion, and selenocentric. The name Diana is connected to dies meaning day, several mechanisms have been proposed for the Moons formation 4.51 billion years ago, and some 60 million years after the origin of the Solar System. These hypotheses also cannot account for the angular momentum of the Earth–Moon system. This hypothesis, although not perfect, perhaps best explains the evidence, eighteen months prior to an October 1984 conference on lunar origins, Bill Hartmann, Roger Phillips, and Jeff Taylor challenged fellow lunar scientists, You have eighteen months. Go back to your Apollo data, go back to computer, do whatever you have to. Dont come to our conference unless you have something to say about the Moons birth, at the 1984 conference at Kona, Hawaii, the giant impact hypothesis emerged as the most popular. Afterward there were only two groups, the giant impact camp and the agnostics. Giant impacts are thought to have been common in the early Solar System, computer simulations of a giant impact have produced results that are consistent with the mass of the lunar core and the present angular momentum of the Earth–Moon system
4.
Gravity
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Gravity, or gravitation, is a natural phenomenon by which all things with mass are brought toward one another, including planets, stars and galaxies. Since energy and mass are equivalent, all forms of energy, including light, on Earth, gravity gives weight to physical objects and causes the ocean tides. Gravity has a range, although its effects become increasingly weaker on farther objects. The most extreme example of this curvature of spacetime is a hole, from which nothing can escape once past its event horizon. More gravity results in time dilation, where time lapses more slowly at a lower gravitational potential. Gravity is the weakest of the four fundamental interactions of nature, the gravitational attraction is approximately 1038 times weaker than the strong force,1036 times weaker than the electromagnetic force and 1029 times weaker than the weak force. As a consequence, gravity has an influence on the behavior of subatomic particles. On the other hand, gravity is the dominant interaction at the macroscopic scale, for this reason, in part, pursuit of a theory of everything, the merging of the general theory of relativity and quantum mechanics into quantum gravity, has become an area of research. While the modern European thinkers are credited with development of gravitational theory, some of the earliest descriptions came from early mathematician-astronomers, such as Aryabhata, who had identified the force of gravity to explain why objects do not fall out when the Earth rotates. Later, the works of Brahmagupta referred to the presence of force, described it as an attractive force. Modern work on gravitational theory began with the work of Galileo Galilei in the late 16th and this was a major departure from Aristotles belief that heavier objects have a higher gravitational acceleration. Galileo postulated air resistance as the reason that objects with less mass may fall slower in an atmosphere, galileos work set the stage for the formulation of Newtons theory of gravity. In 1687, English mathematician Sir Isaac Newton published Principia, which hypothesizes the inverse-square law of universal gravitation. Newtons theory enjoyed its greatest success when it was used to predict the existence of Neptune based on motions of Uranus that could not be accounted for by the actions of the other planets. Calculations by both John Couch Adams and Urbain Le Verrier predicted the position of the planet. A discrepancy in Mercurys orbit pointed out flaws in Newtons theory, the issue was resolved in 1915 by Albert Einsteins new theory of general relativity, which accounted for the small discrepancy in Mercurys orbit. The simplest way to test the equivalence principle is to drop two objects of different masses or compositions in a vacuum and see whether they hit the ground at the same time. Such experiments demonstrate that all objects fall at the rate when other forces are negligible
5.
Radiation pressure
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Radiation pressure is the pressure exerted upon any surface exposed to electromagnetic radiation. Radiation pressure implies an interaction between radiation and bodies of various types, including clouds of particles or gases. The interactions can be absorption, reflection, or some of both, bodies also emit radiation and thereby experience a resulting pressure. For example, had the effects of the radiation pressure on the spacecraft of the Viking program been ignored. This article addresses the macroscopic aspects of radiation pressure, detailed quantum mechanical aspects of interactions are addressed in specialized articles on the subject. The details of how photons of various wavelengths interact with atoms can be explored through links in the See also section, johannes Kepler put forward the concept of radiation pressure back in 1619 to explain the observation that a tail of a comet always points away from the Sun. The pressure is very feeble, but can be detected by allowing the radiation to fall upon a delicately poised vane of reflective metal in a Nichols radiometer, radiation pressure can be analyzed as interactions by either electromagnetic waves or particles. The waves and photons both have the property of momentum, which allows their interchangeability under classical conditions, according to Maxwells theory of electromagnetism, an electromagnetic wave carries momentum, which can be transferred to a reflecting or absorbing surface hit by the wave. The component of the normal to the surface creates the pressure on the surface. The component tangent to the surface does not contribute to the pressure, electromagnetic radiation is quantized in particles called photons, the particle aspect of its wave–particle duality. Photons are best explained by quantum mechanics, although photons are zero-rest mass particles, they have the properties of energy and momentum, and thus exhibit the property of mass as they travel at light speed. The momentum of a photon is given by, p = h λ where p is momentum, h is Plancks constant, λ is wavelength and this expression shows the wave–particle duality. E = p c is the relationship where E is the energy. Then p = E c The generation of radiation pressure results from the property of photons, specifically. The surface exerts a force on the photons in changing their momentum by Newtons Second Law, a reactive force is applied to the body by Newtons Third Law. The orientation of a reflector determines the component of normal to its surface. Each factor contributes a cosine function, reducing the pressure on the surface, bodies radiate thermal energy according to their temperature. The emissions are electromagnetic radiation, and therefore have the properties of energy, the energy leaving a body tends to reduce its temperature
6.
Mineola, New York
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Mineola is a village in Nassau County, Long Island, New York, USA. The population was 18,799 at the 2010 census, the name is derived from an Algonquin word meaning a pleasant place. Most of the Incorporated Village of Mineola is in the Town of North Hempstead, Old Country Road runs along the villages southern border. The area serviced by the Mineola Post Office extends farther south into the adjacent village of Garden City, New York, offices of many Nassau County agencies are in both Mineola and Garden City. The central, flat, grassy part of Long Island was originally named Hempstead Plains, in the 19th century various communities were started. One of them was called Hempstead Branch, and finally, Mineola, Long Island was part of Henry Hudsons original claim in the name of the Dutch East India Company dating as far back as 1609. In the 18th century the Dutch and English settlers worked to clear farmland to start their life on the Hempstead Plains and it was in 1858 when this land was named after an Algonquin Indian Chief, Miniolagamika meaning, Pleasant Village. The name was shortened and altered to Mineola. From about 1787 until the 1870s, the area was the county seat for Queens County, in a section known as Clowesville. The western portion of Queens became a borough of New York City in 1898, voters selected Mineola to be the county seat for the new county of Nassau in November 1898, winning out over Hicksville and Hempstead. The Garden City Company donated four acres of land for the county buildings just south of the Mineola train station, Mineola officially became the County Seat on July 13,1900, as Governor Theodore Roosevelt laid the cornerstone of the Nassau County Court House. A celebration was held to commemorate the occasion on the barren 5-acre site at the corner of Old Country Road, many dignitaries were present to witness this event such as Frederick Hicks, Congressman Townsend Scudder, Colonel William Youngs and Supervisors William Jones and Edwin Willits. Mineola was legally incorporated in 1906 and run by a president, the land on which the County buildings sat was not included as part of the village. The land and the buildings have a Mineola postal address, but are within the present day Village of Garden City, winthrop-University Hospital, founded in 1896 by local physicians and residents as Nassau Hospital, was Long Islands first voluntary hospital. In 1897, it admitted 91 patients, performed 27 operations, the original hospital was constructed in 1900. Renamed Winthrop in the 1980s, it is now a nationally recognized award-winning hospital, Mineola was also a familiar place to many of the most famous pilots in history. The Aero Club of America chose the area for the level plains, glenn Curtiss brought the area to national attention in July 1909 with his second Scientific American Award flight of over 23 minutes and 15 miles. He also made some of the first public flights in America in his Golden Flyer and it was the Guards first genuine aviation unit
7.
YouTube
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YouTube is an American video-sharing website headquartered in San Bruno, California. The service was created by three former PayPal employees—Chad Hurley, Steve Chen, and Jawed Karim—in February 2005, Google bought the site in November 2006 for US$1.65 billion, YouTube now operates as one of Googles subsidiaries. Unregistered users can watch videos on the site, while registered users are permitted to upload an unlimited number of videos. Videos deemed potentially offensive are available only to registered users affirming themselves to be at least 18 years old, YouTube earns advertising revenue from Google AdSense, a program which targets ads according to site content and audience. YouTube was founded by Chad Hurley, Steve Chen, and Jawed Karim, Hurley had studied design at Indiana University of Pennsylvania, and Chen and Karim studied computer science together at the University of Illinois at Urbana-Champaign. Karim could not easily find video clips of either event online, Hurley and Chen said that the original idea for YouTube was a video version of an online dating service, and had been influenced by the website Hot or Not. YouTube began as a venture capital-funded technology startup, primarily from an $11.5 million investment by Sequoia Capital between November 2005 and April 2006, YouTubes early headquarters were situated above a pizzeria and Japanese restaurant in San Mateo, California. The domain name www. youtube. com was activated on February 14,2005, the first YouTube video, titled Me at the zoo, shows co-founder Jawed Karim at the San Diego Zoo. The video was uploaded on April 23,2005, and can still be viewed on the site, YouTube offered the public a beta test of the site in May 2005. The first video to reach one million views was a Nike advertisement featuring Ronaldinho in November 2005. Following a $3.5 million investment from Sequoia Capital in November, the site grew rapidly, and in July 2006 the company announced that more than 65,000 new videos were being uploaded every day, and that the site was receiving 100 million video views per day. The site has 800 million unique users a month and it is estimated that in 2007 YouTube consumed as much bandwidth as the entire Internet in 2000. The choice of the name www. youtube. com led to problems for a similarly named website, the sites owner, Universal Tube & Rollform Equipment, filed a lawsuit against YouTube in November 2006 after being regularly overloaded by people looking for YouTube. Universal Tube has since changed the name of its website to www. utubeonline. com, in October 2006, Google Inc. announced that it had acquired YouTube for $1.65 billion in Google stock, and the deal was finalized on November 13,2006. In March 2010, YouTube began free streaming of certain content, according to YouTube, this was the first worldwide free online broadcast of a major sporting event. On March 31,2010, the YouTube website launched a new design, with the aim of simplifying the interface, Google product manager Shiva Rajaraman commented, We really felt like we needed to step back and remove the clutter. In May 2010, YouTube videos were watched more than two times per day. This increased to three billion in May 2011, and four billion in January 2012, in February 2017, one billion hours of YouTube was watched every day
8.
Solar wind
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The solar wind is a stream of charged particles released from the upper atmosphere of the Sun. This plasma consists of electrons, protons and alpha particles with thermal energies between 1.5 and 10 keV. Embedded within the plasma is the interplanetary magnetic field. The solar wind varies in density, temperature and speed over time and its particles can escape the Suns gravity because of their high energy resulting from the high temperature of the corona, which in turn is a result of the coronal magnetic field. At a distance of more than a few radii from the sun. The flow of the wind is no longer supersonic at the termination shock. The Voyager 2 spacecraft crossed the shock more than five times between 30 August and 10 December 2007, Voyager 2 crossed the shock about a billion kilometers closer to the Sun than the 13.5 billion kilometer distance where Voyager 1 came upon the termination shock. The spacecraft moved outward through the shock into the heliosheath. Other related phenomena include the aurora, the tails of comets that always point away from the Sun. The existence of flowing outward from the Sun to the Earth was first suggested by British astronomer Richard C. In 1859, Carrington and Richard Hodgson independently made the first observation of what would later be called a solar flare, george FitzGerald later suggested that matter was being regularly accelerated away from the Sun and was reaching the Earth after several days. In 1910 British astrophysicist Arthur Eddington essentially suggested the existence of the wind, without naming it. The idea never caught on even though Eddington had also made a similar suggestion at a Royal Institution address the previous year. In the latter case, he postulated that the material consisted of electrons while in his study of Comet Morehouse he supposed them to be ions. The first person to suggest that the material consisted of both ions and electrons was Kristian Birkeland. His geomagnetic surveys showed that activity was nearly uninterrupted. In 1916, Birkeland proposed that, From a physical point of view it is most probable that solar rays are neither exclusively negative nor positive rays, in other words, the solar wind consists of both negative electrons and positive ions. Three years later in 1919, Frederick Lindemann also suggested that particles of both polarities, protons as well as electrons, come from the Sun
9.
Orbit
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In physics, an orbit is the gravitationally curved path of an object around a point in space, for example the orbit of a planet about a star or a natural satellite around a planet. Normally, orbit refers to a regularly repeating path around a body, to a close approximation, planets and satellites follow elliptical orbits, with the central mass being orbited at a focal point of the ellipse, as described by Keplers laws of planetary motion. For ease of calculation, in most situations orbital motion is adequately approximated by Newtonian Mechanics, historically, the apparent motions of the planets were described by European and Arabic philosophers using the idea of celestial spheres. This model posited the existence of perfect moving spheres or rings to which the stars and it assumed the heavens were fixed apart from the motion of the spheres, and was developed without any understanding of gravity. After the planets motions were accurately measured, theoretical mechanisms such as deferent. Originally geocentric it was modified by Copernicus to place the sun at the centre to help simplify the model, the model was further challenged during the 16th century, as comets were observed traversing the spheres. The basis for the understanding of orbits was first formulated by Johannes Kepler whose results are summarised in his three laws of planetary motion. Second, he found that the speed of each planet is not constant, as had previously been thought. Third, Kepler found a relationship between the orbital properties of all the planets orbiting the Sun. For the planets, the cubes of their distances from the Sun are proportional to the squares of their orbital periods. Jupiter and Venus, for example, are respectively about 5.2 and 0.723 AU distant from the Sun, their orbital periods respectively about 11.86 and 0.615 years. The proportionality is seen by the fact that the ratio for Jupiter,5. 23/11.862, is equal to that for Venus,0. 7233/0.6152. Idealised orbits meeting these rules are known as Kepler orbits, isaac Newton demonstrated that Keplers laws were derivable from his theory of gravitation and that, in general, the orbits of bodies subject to gravity were conic sections. Newton showed that, for a pair of bodies, the sizes are in inverse proportion to their masses. Where one body is more massive than the other, it is a convenient approximation to take the center of mass as coinciding with the center of the more massive body. Lagrange developed a new approach to Newtonian mechanics emphasizing energy more than force, in a dramatic vindication of classical mechanics, in 1846 le Verrier was able to predict the position of Neptune based on unexplained perturbations in the orbit of Uranus. This led astronomers to recognize that Newtonian mechanics did not provide the highest accuracy in understanding orbits, in relativity theory, orbits follow geodesic trajectories which are usually approximated very well by the Newtonian predictions but the differences are measurable. Essentially all the evidence that can distinguish between the theories agrees with relativity theory to within experimental measurement accuracy
10.
Rocket engine
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A rocket engine is a type of jet engine that uses only stored rocket propellant mass for forming its high speed propulsive jet. Rocket engines are reaction engines, obtaining thrust in accordance with Newtons third law, most rocket engines are internal combustion engines, although non-combusting forms also exist. Vehicles propelled by rocket engines are commonly called rockets, since they need no external material to form their jet, rocket engines can perform in a vacuum and thus can be used to propel spacecraft and ballistic missiles. Compared to other types of jet engines, rocket engines have the highest thrust, are by far the lightest, the ideal exhaust is hydrogen, the lightest of all gases, but chemical rockets produce a mix of heavier species, reducing the exhaust velocity. Rocket engines become more efficient at high velocities, since they do not require an atmosphere, they are well suited for uses at very high altitude and in space. Here, rocket is used as an abbreviation for rocket engine, chemical rockets are powered by exothermic chemical reactions of the propellant. Thermal rockets use a propellant, heated by a power source such as electric or nuclear power. Solid-fuel rockets are chemical rockets which use propellant in a solid state, liquid-propellant rockets use one or more liquid propellants fed from tanks. Hybrid rockets use a propellant in the combustion chamber, to which a second liquid or gas oxidiser or propellant is added to permit combustion. Monopropellant rockets use a single propellant decomposed by a catalyst, the most common monopropellants are hydrazine and hydrogen peroxide. Rocket engines produce thrust by the expulsion of an exhaust fluid which has accelerated to a high speed through a propelling nozzle. The fluid is usually a gas created by high pressure combustion of solid or liquid propellants, consisting of fuel and oxidiser components, within a combustion chamber. The nozzle uses the energy released by expansion of the gas to accelerate the exhaust to very high speed. An alternative to combustion is the rocket, which uses water pressurised by compressed air, carbon dioxide, nitrogen, or manual pumping. Chemical rocket propellants are most commonly used, which undergo exothermic chemical reactions which produce hot gas which is used by a rocket for propulsive purposes. Alternatively, a chemically inert reaction mass can be heated using a power source via a heat exchanger. Solid rocket propellants are prepared as a mixture of fuel and oxidising components called grain, liquid-fuelled rockets force separate fuel and oxidiser components into the combustion chamber, where they mix and burn. Hybrid rocket engines use a combination of solid and liquid or gaseous propellants, both liquid and hybrid rockets use injectors to introduce the propellant into the chamber
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