1.
Hubble Space Telescope
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The Hubble Space Telescope is a space telescope that was launched into low Earth orbit in 1990 and remains in operation. Although not the first space telescope, Hubble is one of the largest and most versatile, with a 2. 4-meter mirror, Hubbles four main instruments observe in the near ultraviolet, visible, and near infrared spectra. Hubbles orbit outside the distortion of Earths atmosphere allows it to take extremely high-resolution images, Hubble has recorded some of the most detailed visible light images ever, allowing a deep view into space and time. Many Hubble observations have led to breakthroughs in astrophysics, such as determining the rate of expansion of the universe. The HST was built by the United States space agency NASA, the Space Telescope Science Institute selects Hubbles targets and processes the resulting data, while the Goddard Space Flight Center controls the spacecraft. Space telescopes were proposed as early as 1923, Hubble was funded in the 1970s, with a proposed launch in 1983, but the project was beset by technical delays, budget problems, and the Challenger disaster. When finally launched in 1990, Hubbles main mirror was found to have been ground incorrectly, the optics were corrected to their intended quality by a servicing mission in 1993. Hubble is the telescope designed to be serviced in space by astronauts. After launch by Space Shuttle Discovery in 1990, five subsequent Space Shuttle missions repaired, upgraded, the fifth mission was canceled on safety grounds following the Columbia disaster. However, after spirited public discussion, NASA administrator Mike Griffin approved the fifth servicing mission, the telescope is operating as of 2017, and could last until 2030–2040. Its scientific successor, the James Webb Space Telescope, is scheduled for launch in 2018, the history of the Hubble Space Telescope can be traced back as far as 1946, to the astronomer Lyman Spitzers paper Astronomical advantages of an extraterrestrial observatory. In it, he discussed the two advantages that a space-based observatory would have over ground-based telescopes. First, the resolution would be limited only by diffraction, rather than by the turbulence in the atmosphere. Second, a telescope could observe infrared and ultraviolet light. Spitzer devoted much of his career to pushing for the development of a space telescope, space-based astronomy had begun on a very small scale following World War II, as scientists made use of developments that had taken place in rocket technology. An orbiting solar telescope was launched in 1962 by the United Kingdom as part of the Ariel space program, oAO-1s battery failed after three days, terminating the mission. It was followed by OAO-2, which carried out observations of stars and galaxies from its launch in 1968 until 1972. The continuing success of the OAO program encouraged increasingly strong consensus within the community that the LST should be a major goal
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.
Pluto
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Pluto is a dwarf planet in the Kuiper belt, a ring of bodies beyond Neptune. It was the first Kuiper belt object to be discovered, Pluto was discovered by Clyde Tombaugh in 1930 and was originally considered to be the ninth planet from the Sun. After 1992, its planethood was questioned following the discovery of objects of similar size in the Kuiper belt. In 2005, Eris, which is 27% more massive than Pluto, was discovered and this led the International Astronomical Union to define the term planet formally in 2006, during their 26th General Assembly. That definition excluded Pluto and reclassified it as a dwarf planet, Pluto is the largest and second-most-massive known dwarf planet in the Solar System and the ninth-largest and tenth-most-massive known object directly orbiting the Sun. It is the largest known trans-Neptunian object by volume but is less massive than Eris, like other Kuiper belt objects, Pluto is primarily made of ice and rock and is relatively small—about one-sixth the mass of the Moon and one-third its volume. It has an eccentric and inclined orbit during which it ranges from 30 to 49 astronomical units or AU from the Sun. This means that Pluto periodically comes closer to the Sun than Neptune, light from the Sun takes about 5.5 hours to reach Pluto at its average distance. Pluto has five moons, Charon, Styx, Nix, Kerberos. Pluto and Charon are sometimes considered a system because the barycenter of their orbits does not lie within either body. The IAU has not formalized a definition for binary dwarf planets, on July 14,2015, the New Horizons spacecraft became the first spacecraft to fly by Pluto. During its brief flyby, New Horizons made detailed measurements and observations of Pluto, on October 25,2016, at 05,48 pm ET, the last bit of data was received from New Horizons from its close encounter with Pluto on July 14,2015. In the 1840s, Urbain Le Verrier used Newtonian mechanics to predict the position of the then-undiscovered planet Neptune after analysing perturbations in the orbit of Uranus. Subsequent observations of Neptune in the late 19th century led astronomers to speculate that Uranuss orbit was being disturbed by another planet besides Neptune, by 1909, Lowell and William H. Pickering had suggested several possible celestial coordinates for such a planet. Lowell and his observatory conducted his search until his death in 1916, unknown to Lowell, his surveys had captured two faint images of Pluto on March 19 and April 7,1915, but they were not recognized for what they were. There are fourteen other known prediscovery observations, with the oldest made by the Yerkes Observatory on August 20,1909. Percivals widow, Constance Lowell, entered into a legal battle with the Lowell Observatory over her late husbands legacy. Tombaughs task was to image the night sky in pairs of photographs, then examine each pair
4.
Mass
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In physics, mass is a property of a physical body. It is the measure of a resistance to acceleration when a net force is applied. It also determines the strength of its gravitational attraction to other bodies. The basic SI unit of mass is the kilogram, Mass is not the same as weight, even though mass is often determined by measuring the objects weight using a spring scale, rather than comparing it directly with known masses. An object on the Moon would weigh less than it does on Earth because of the lower gravity and this is because weight is a force, while mass is the property that determines the strength of this force. In Newtonian physics, mass can be generalized as the amount of matter in an object, however, at very high speeds, special relativity postulates that energy is an additional source of mass. Thus, any body having mass has an equivalent amount of energy. In addition, matter is a defined term in science. There are several distinct phenomena which can be used to measure mass, active gravitational mass measures the gravitational force exerted by an object. Passive gravitational mass measures the force exerted on an object in a known gravitational field. The mass of an object determines its acceleration in the presence of an applied force, according to Newtons second law of motion, if a body of fixed mass m is subjected to a single force F, its acceleration a is given by F/m. A bodys mass also determines the degree to which it generates or is affected by a gravitational field and this is sometimes referred to as gravitational mass. The standard International System of Units unit of mass is the kilogram, the kilogram is 1000 grams, first defined in 1795 as one cubic decimeter of water at the melting point of ice. Then in 1889, the kilogram was redefined as the mass of the prototype kilogram. As of January 2013, there are proposals for redefining the kilogram yet again. In this context, the mass has units of eV/c2, the electronvolt and its multiples, such as the MeV, are commonly used in particle physics. The atomic mass unit is 1/12 of the mass of a carbon-12 atom, the atomic mass unit is convenient for expressing the masses of atoms and molecules. Outside the SI system, other units of mass include, the slug is an Imperial unit of mass, the pound is a unit of both mass and force, used mainly in the United States
5.
Moons of Pluto
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The dwarf planet Pluto has five moons down to a detection limit of about 1 km in diameter. In order of distance from Pluto, they are Charon, Styx, Nix, Kerberos, Charon, the largest of the five moons, is mutually tidally locked with Pluto, and is massive enough that Pluto–Charon is sometimes considered a double dwarf planet. The innermost and largest moon, Charon, was discovered by James Christy on 22 June 1978 and this led to a substantial revision in estimates of Plutos size, which had previously assumed that the observed mass and reflected light of the system were all attributable to Pluto alone. The International Astronomical Union officially named these moons Nix and Hydra, Styx, announced on 7 July 2012, was discovered while looking for potential hazards for New Horizons. Charon is about half the diameter of Pluto and is so massive that the barycenter lies between them, approximately 960 km above Plutos surface. Charon and Pluto are also locked, so that they always present the same face toward each other. The IAU General Assembly in August 2006 considered a proposal that Pluto and Charon be reclassified as a double planet, but the proposal was abandoned. Plutos four small moons orbit Pluto at two to four times the distance of Charon, ranging from Styx at 42,700 kilometres to Hydra at 64,800 kilometres from the barycenter of the system and they have nearly circular prograde orbits in the same orbital plane as Charon. All are much smaller than Charon, Nix and Hydra, the two larger, are roughly 42 and 55 kilometers on their longest axis respectively, and Styx and Kerberos are 7 and 12 kilometers respectively. The Pluto system is compact and largely empty. Moons could potentially orbit Pluto at up to 53% of the Hill radius, for example, Psamathe orbits Neptune at 40% of the Hill radius. An intense search conducted by New Horizons confirmed that no larger than 4.5 km in diameter exist at the distances up to 180,000 km from Pluto. Further information is expected as more data from the New Horizons flyby is sent back to Earth. The orbits of the moons are confirmed to be circular and coplanar, with inclinations differing less than 0. 4°, as seen from Earth, these circular orbits appear foreshortened into ellipses depending on Plutos position. The discovery of Nix and Hydra suggested that Pluto could have a ring system, small-body impacts can create debris that can form into a ring system. However, data from a survey by the Advanced Camera for Surveys on the Hubble Space Telescope, by occultation studies. Styx, Nix, and Hydra are thought to be in a 3-body orbital resonance with orbital periods in a ratio of 18,22,33, the ratios should be exact when orbital precession is taken into account. This means that in a recurring cycle there are 11 orbits of Styx for every 9 of Nix and 6 of Hydra, putting Nix and Hydra into a simple 2,3 resonance
6.
Hydra (moon)
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Hydra is the outermost known moon of Pluto. It was discovered along with Nix in June 2005, and was visited along with Pluto by New Horizons in July 2015, Hydras surface is probably covered with water ice. Observed within Hydras bright regions is a circular structure with a diameter of approximately 10 kilometers. Hydras reflectivity is intermediate between those of Pluto and Charon, the discovery images were taken on 15 May 2005, and 18 May 2005, Nix and Hydra were independently discovered by Max J. Mutchler on 15 June 2005, and Andrew J. Steffl on 15 August 2005. The discoveries were announced on 31 October 2005, after confirmation by precoveries from 2002 and they were provisionally designated S/2005 P1 and S/2005 P2. The name Hydra was announced on 21 June 2006, in IAU Circular 8723, the name is that of the Hydra, the nine-headed serpent that battled Heracles in Greek mythology. Hydra orbits the barycenter of the system in the plane as Charon and Nix. Its eccentricity of 0.0059 is small, but significantly non-zero, Hydra is in a 2,3 orbital resonance with Nix, and a 6,11 resonance with Styx. As a result of this Laplace-like 3-body resonance, it has conjunctions with Styx and its orbital period of 38.2 days is also close to a 1,6 orbital resonance with Charon, with the timing discrepancy being 0. 3%. This is largely due to the fluctuation of the Pluto–Charon gravitational field. Hydras current rotational period is a mere 10 hours, Hydra is irregular in shape,55 by 40 kilometers in cross-section from one side. It is spectrally neutral like Charon and most of Nix and is composed primarily of water ice, the only detailed photographs of Hydra were taken by the New Horizons spacecraft from approximately 640,000 kilometres away during its flyby of the Pluto–Charon system on 14 July 2015. It also studied Hydras surface composition, reflectivity, and other physical properties. Hydras reflectivity is estimated to be about 45 percent. Sources Steffl, A. J. Mutchler, M. J. Weaver, H. A. Stern, S. A. Durda, D. D. Terrell, D. Merline, W. J. Young, L. A. Young, E. F. Buie, M. W. & Spencer, J. R. New Constraints on Additional Satellites of the Pluto System
7.
Charon (mythology)
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A coin to pay Charon for passage, usually an obolus or danake, was sometimes placed in or on the mouth of a dead person. Some authors say that those who could not pay the fee, Charon is the son of Nyx and Erebus. Nyx and Erebus were brother and sister and he was also the brother of Thanatos and Hypnos. The word may be a euphemism for death, flashing eyes may indicate the anger or irascibility of Charon as he is often characterized in literature, but the etymology is not certain. The ancient historian Diodorus Siculus thought that the ferryman and his name had been imported from Egypt, Charon is depicted frequently in the art of ancient Greece. Attic funerary vases of the 5th and 4th centuries BC are often decorated with scenes of the dead boarding Charon’s boat. On the earlier such vases, he looks like a rough, unkempt Athenian seaman dressed in reddish-brown, holding his ferrymans pole in his right hand, hermes sometimes stands by in his role as psychopomp. On later vases, Charon is given a more “kindly and refined” demeanor, when the boatman tells Hercules to halt, the Greek hero uses his strength to gain passage, overpowering Charon with the boatmans own pole. In the second century, Lucian employed Charon as a figure in his Dialogues of the Dead, in the 14th century, Dante Alighieri described Charon in his Divine Comedy, drawing from Virgils depiction in Aeneid 6. Charon is the first named mythological character Dante meets in the underworld, Dante depicts him as having eyes of fire. In modern times, he is depicted as a living skeleton in a cowl. The French artist, Gustave Dore, depicted Charon in two of his illustrations for Dantes Divine Comedy, the Flemish painter, Joachim Patinir, depicted Charon in his Crossing the River Styx. And the Spanish painter, Jose Benlliure y Gil, portrayed Charon in his La Barca de Caronte, most accounts, including Pausanias and later Dantes Inferno, associate Charon with the swamps of the river Acheron. Ancient Greek literary sources – such as Pindar, Aeschylus, Euripides, Plato, roman poets, including Propertius, Ovid, and Statius, name the river as the Styx, perhaps following the geography of Virgil’s underworld in the Aeneid, where Charon is associated with both rivers. Charon, the dwarf planet of the Pluto-Charon system, is named after him. Haros is the modern Greek equivalent of Charon, and usage includes the curse you will be eaten by Haros, during the Korean War, the Greek Expeditionary Force defended an outpost called Outpost Harry. The Greek soldiers referred to it as Outpost Haros, Charon Media related to Charon at Wikimedia Commons The Theoi Project, KHARON Images of Charon in the Warburg Institute Iconographic Database
8.
Hades
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Hades was the ancient Greek chthonic god of the underworld, which eventually took his name. In Greek mythology, Hades was regarded as the oldest son of Cronus and Rhea and he and his brothers Zeus and Poseidon defeated their fathers generation of gods, the Titans, and claimed rulership over the cosmos. Hades received the underworld, Zeus the sky, and Poseidon the sea, Hades was often portrayed with his three-headed guard dog Cerberus. The Etruscan god Aita and Roman gods Dis Pater and Orcus were eventually taken as equivalent to the Greek Hades and merged as Pluto, the origin of Hades name is uncertain, but has generally been seen as meaning The Unseen One since antiquity. Modern linguists have proposed the Proto-Greek form *Awides, the earliest attested form is Aḯdēs, which lacks the proposed digamma. West argues instead for a meaning of the one who presides over meeting up from the universality of death. In Homeric and Ionic Greek, he was known as Áïdēs, other poetic variations of the name include Aïdōneús and the inflected forms Áïdos, Áïdi, and Áïda, whose reconstructed nominative case *Áïs is, however, not attested. The name as it came to be known in classical times was Háidēs, later the iota became silent, then a subscript marking, and finally omitted entirely. Perhaps from fear of pronouncing his name, around the 5th century BC, Plouton became the Roman god who both rules the underworld and distributed riches from below. This deity was a mixture of the Greek god Hades and the Eleusinian icon Ploutos, and from this he received a priestess. More elaborate names of the genre were Ploutodótēs or Ploutodotḗr meaning giver of wealth. Epithets of Hades include Agesander and Agesilaos, both from ágō and anḗr or laos, describing Hades as the god who carries away all. He was also referred to as Zeus Katachthonios, meaning the Zeus of the Underworld, by avoiding his actual name. In Greek mythology, Hades the god of the underworld, was a son of the Titans Cronus and he had three sisters, Demeter, Hestia, and Hera, as well as two brothers, Zeus, the youngest of the three, and Poseidon. Upon reaching adulthood, Zeus managed to force his father to disgorge his siblings, after their release, the six younger gods, along with allies they managed to gather, challenged the elder gods for power in the Titanomachy, a divine war. The war lasted for ten years and ended with the victory of the younger gods, following their victory, according to a single famous passage in the Iliad, Hades and his two brothers, Poseidon and Zeus, drew lots for realms to rule. Some myths suggest that Hades was dissatisfied with his turnout, but had no choice, Hades obtained his wife and queen, Persephone, through abduction at the behest of Zeus. Despite modern connotations of death as evil, Hades was actually more altruistically inclined in mythology, Hades was often portrayed as passive rather than evil, his role was often maintaining relative balance
9.
Asteroid
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Asteroids are minor planets, especially those of the inner Solar System. The larger ones have also been called planetoids and these terms have historically been applied to any astronomical object orbiting the Sun that did not show the disc of a planet and was not observed to have the characteristics of an active comet. As minor planets in the outer Solar System were discovered and found to have volatile-based surfaces that resemble those of comets, in this article, the term asteroid refers to the minor planets of the inner Solar System including those co-orbital with Jupiter. There are millions of asteroids, many thought to be the remnants of planetesimals. The large majority of known asteroids orbit in the belt between the orbits of Mars and Jupiter, or are co-orbital with Jupiter. However, other orbital families exist with significant populations, including the near-Earth objects, individual asteroids are classified by their characteristic spectra, with the majority falling into three main groups, C-type, M-type, and S-type. These were named after and are identified with carbon-rich, metallic. The size of asteroids varies greatly, some reaching as much as 1000 km across, asteroids are differentiated from comets and meteoroids. In the case of comets, the difference is one of composition, while asteroids are composed of mineral and rock, comets are composed of dust. In addition, asteroids formed closer to the sun, preventing the development of the aforementioned cometary ice, the difference between asteroids and meteoroids is mainly one of size, meteoroids have a diameter of less than one meter, whereas asteroids have a diameter of greater than one meter. Finally, meteoroids can be composed of either cometary or asteroidal materials, only one asteroid,4 Vesta, which has a relatively reflective surface, is normally visible to the naked eye, and this only in very dark skies when it is favorably positioned. Rarely, small asteroids passing close to Earth may be visible to the eye for a short time. As of March 2016, the Minor Planet Center had data on more than 1.3 million objects in the inner and outer Solar System, the United Nations declared June 30 as International Asteroid Day to educate the public about asteroids. The date of International Asteroid Day commemorates the anniversary of the Tunguska asteroid impact over Siberia, the first asteroid to be discovered, Ceres, was found in 1801 by Giuseppe Piazzi, and was originally considered to be a new planet. In the early half of the nineteenth century, the terms asteroid. Asteroid discovery methods have improved over the past two centuries. This task required that hand-drawn sky charts be prepared for all stars in the band down to an agreed-upon limit of faintness. On subsequent nights, the sky would be charted again and any moving object would, hopefully, the expected motion of the missing planet was about 30 seconds of arc per hour, readily discernible by observers
10.
Charon (moon)
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Charon, also known as Pluto I, is the largest of the five known natural satellites of the dwarf planet Pluto. It was discovered in 1978 at the United States Naval Observatory in Washington, with half the diameter and one eighth the mass of Pluto, it is a very large moon in comparison to its parent body. Its gravitational influence is such that the barycenter of the Pluto–Charon system lies outside Pluto, the New Horizons spacecraft is the only probe that has visited the Pluto system. It approached Charon to within 27,000 km, Charon was discovered by United States Naval Observatory astronomer James Christy, using the 1. 55-meter Flagstaff telescope two months prior. Christy noticed that a slight elongation appeared periodically, later, the bulge was confirmed on plates dating back to April 29,1965. Subsequent observations of Pluto determined that the bulge was due to an accompanying body. The periodicity of the bulge corresponded to Plutos rotation period, which was known from Plutos light curve. This indicated a synchronous orbit, which suggested that the bulge effect was real. Doubts about Charons existence were erased when it and Pluto entered a period of mutual eclipses. This occurs when the Pluto–Charon orbital plane is edge-on as seen from Earth and it was fortuitous that one of these intervals happened to occur soon after Charons discovery. Charon was originally known by the temporary designation S/1978 P1, on June 24,1978, Christy first suggested the name Charon as a scientific-sounding version of his wife Charlenes nickname, Char. The IAU officially adopted the name in late 1985 and it was announced on January 3,1986, there is minor debate over the preferred pronunciation of the name. These indicate only one pronunciation of Charon when referring specifically to Plutos moon, speakers of many languages other than English, and many English-speaking astronomers as well, follow this pronunciation. However, Christy himself pronounced the ch as sh, after his wife Charlene, simulation work published in 2005 by Robin Canup suggested that Charon could have been formed by a collision around 4.5 billion years ago, much like Earth and the Moon. In this model, a large Kuiper belt object struck Pluto at high velocity, destroying itself and blasting off much of Plutos outer mantle, however, such an impact should result in an icier Charon and rockier Pluto than scientists have found. It is now thought that Pluto and Charon might have been two bodies that collided before going into orbit about each other, the collision would have been violent enough to boil off volatile ices like methane but not violent enough to have destroyed either body. The very similar density of Pluto and Charon implies that the parent bodies were not fully differentiated when the impact occurred, Charon and Pluto orbit each other every 6.387 days. The two objects are locked to one another, so each keeps the same face towards the other
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. Bibcode:2015Sci...350.1815S. doi:10.1126/science.aad1815. PMID 26472913.
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