The scattered disc is a distant circumstellar disc in the Solar System, sparsely populated by icy small solar system bodies, which are a subset of the broader family of trans-Neptunian objects. The scattered-disc objects have orbital eccentricities ranging as high as 0.8, inclinations as high as 40°, perihelia greater than 30 astronomical units. These extreme orbits are thought to be the result of gravitational "scattering" by the gas giants, the objects continue to be subject to perturbation by the planet Neptune. Although the closest scattered-disc objects approach the Sun at about 30–35 AU, their orbits can extend well beyond 100 AU; this makes scattered objects among most distant objects in the Solar System. The innermost portion of the scattered disc overlaps with a torus-shaped region of orbiting objects traditionally called the Kuiper belt, but its outer limits reach much farther away from the Sun and farther above and below the ecliptic than the Kuiper belt proper; because of its unstable nature, astronomers now consider the scattered disc to be the place of origin for most periodic comets in the Solar System, with the centaurs, a population of icy bodies between Jupiter and Neptune, being the intermediate stage in an object's migration from the disc to the inner Solar System.
Perturbations from the giant planets send such objects towards the Sun, transforming them into periodic comets. Many objects of the proposed Oort cloud are thought to have originated in the scattered disc. Detached objects are not distinct from scattered disc objects, some such as Sedna have sometimes been considered to be included in this group. Traditionally, devices like a blink comparator were used in astronomy to detect objects in the Solar System, because these objects would move between two exposures—this involved time-consuming steps like exposing and developing photographic plates or films, people using a blink comparator to manually detect prospective objects. During the 1980s, the use of CCD-based cameras in telescopes made it possible to directly produce electronic images that could be digitized and transferred to digital images; because the CCD captured more light than film and the blinking could now be done at an adjustable computer screen, the surveys allowed for higher throughput.
A flood of new discoveries was the result: over a thousand trans-Neptunian objects were detected between 1992 and 2006. The first scattered-disc object to be recognised as such was 1996 TL66 identified in 1996 by astronomers based at Mauna Kea in Hawaii. Three more were identified by the same survey in 1999: 1999 CV118, 1999 CY118, 1999 CF119; the first object presently classified as an SDO to be discovered was 1995 TL8, found in 1995 by Spacewatch. As of 2011, over 200 SDOs have been identified, including Gǃkúnǁʼhòmdímà, 2002 TC302, Sedna and 2004 VN112. Although the numbers of objects in the Kuiper belt and the scattered disc are hypothesized to be equal, observational bias due to their greater distance means that far fewer SDOs have been observed to date. Known trans-Neptunian objects are divided into two subpopulations: the Kuiper belt and the scattered disc. A third reservoir of trans-Neptunian objects, the Oort cloud, has been hypothesized, although no confirmed direct observations of the Oort cloud have been made.
Some researchers further suggest a transitional space between the scattered disc and the inner Oort cloud, populated with "detached objects". The Kuiper belt is a thick torus of space, extending from about 30 to 50 AU comprising two main populations of Kuiper belt objects: the classical Kuiper-belt objects, which lie in orbits untouched by Neptune, the resonant Kuiper-belt objects; these ratios, called orbital resonances, allow KBOs to persist in regions which Neptune's gravitational influence would otherwise have cleared out over the age of the Solar System, since the objects are never close enough to Neptune to be scattered by its gravity. Those in 2:3 resonances are known as "plutinos", because Pluto is the largest member of their group, whereas those in 1:2 resonances are known as "twotinos". In contrast to the Kuiper belt, the scattered-disc population can be disturbed by Neptune. Scattered-disc objects come within gravitational range of Neptune at their closest approaches but their farthest distances reach many times that.
Ongoing research suggests that the centaurs, a class of icy planetoids that orbit between Jupiter and Neptune, may be SDOs thrown into the inner reaches of the Solar System by Neptune, making them "cis-Neptunian" rather than trans-Neptunian scattered objects. Some objects, like 1999 TD10, blur the distinction and the Minor Planet Center, which catalogues all trans-Neptunian objects, now lists centaurs and SDOs together; the MPC, makes a clear distinction between the Kuiper belt and the scattered disc, separating those objects in stable orbits from those in scattered orbits. However, the difference between the Kuiper belt and the scattered disc is not clear-cut, many astronomers see the scattered disc not as a separate population but as an outward region of the Kuiper belt. Another term used is "scattered Kuiper-belt object" for bodies of the scattered d
The Jupiter trojans called Trojan asteroids or Trojans, are a large group of asteroids that share the planet Jupiter's orbit around the Sun. Relative to Jupiter, each Trojan librates around one of Jupiter's two stable Lagrange points: L4, lying 60° ahead of the planet in its orbit, L5, 60° behind. Jupiter trojans are distributed in two elongated, curved regions around these Lagrangian points with an average semi-major axis of about 5.2 AU. The first Jupiter trojan discovered, 588 Achilles, was spotted in 1906 by German astronomer Max Wolf. A total of 7,040 Jupiter trojans have been found as of October 2018. By convention, they are each named from Greek mythology after a figure of the Trojan War, hence the name "Trojan"; the total number of Jupiter trojans larger than 1 km in diameter is believed to be about 1 million equal to the number of asteroids larger than 1 km in the asteroid belt. Like main-belt asteroids, Jupiter trojans form families. Jupiter trojans are dark bodies with featureless spectra.
No firm evidence of the presence of water, or any other specific compound on their surface has been obtained, but it is thought that they are coated in tholins, organic polymers formed by the Sun's radiation. The Jupiter trojans' densities vary from 0.8 to 2.5 g·cm−3. Jupiter trojans are thought to have been captured into their orbits during the early stages of the Solar System's formation or later, during the migration of giant planets; the term "Trojan Asteroid" refers to the asteroids co-orbital with Jupiter, but the general term "trojan" is sometimes more applied to other small Solar System bodies with similar relationships to larger bodies: for example, there are both Mars trojans and Neptune trojans, as well as a recently-discovered Earth trojan. The term "Trojan asteroid" is understood to mean the Jupiter trojans because the first Trojans were discovered near Jupiter's orbit and Jupiter has by far the most known Trojans. In 1772, Italian-born mathematician Joseph-Louis Lagrange, in studying the restricted three-body problem, predicted that a small body sharing an orbit with a planet but lying 60° ahead or behind it will be trapped near these points.
The trapped body will librate around the point of equilibrium in a tadpole or horseshoe orbit. These leading and trailing points are called the L5 Lagrange points; the first asteroids trapped in Lagrange points were observed more than a century after Lagrange's hypothesis. Those associated with Jupiter were the first to be discovered. E. E. Barnard made the first recorded observation of a trojan, 1999 RM11, in 1904, but neither he nor others appreciated its significance at the time. Barnard believed he had seen the discovered Saturnian satellite Phoebe, only two arc-minutes away in the sky at the time, or an asteroid; the object's identity was not understood until its orbit was calculated in 1999. The first accepted discovery of a trojan occurred in February 1906, when astronomer Max Wolf of Heidelberg-Königstuhl State Observatory discovered an asteroid at the L4 Lagrangian point of the Sun–Jupiter system named 588 Achilles. In 1906–1907 two more Jupiter trojans were found by fellow German astronomer August Kopff.
Hektor, like Achilles, belonged to the L4 swarm, whereas Patroclus was the first asteroid known to reside at the L5 Lagrangian point. By 1938, 11 Jupiter trojans had been detected; this number increased to 14 only in 1961. As instruments improved, the rate of discovery grew rapidly: by January 2000, a total of 257 had been discovered; as of October 2018 there are 4,601 known Jupiter trojans at L4 and 2,439 at L5. The custom of naming all asteroids in Jupiter's L4 and L5 points after famous heroes of the Trojan War was suggested by Johann Palisa of Vienna, the first to calculate their orbits. Asteroids in the leading orbit are named after Greek heroes, those at the trailing orbit are named after the heroes of Troy; the asteroids 617 Patroclus and 624 Hektor were named before the Greece/Troy rule was devised, resulting in a Greek spy in the Trojan node and a Trojan spy in the Greek node. Estimates of the total number of Jupiter trojans are based on deep surveys of limited areas of the sky; the L4 swarm is believed to hold between 160–240,000 asteroids with diameters larger than 2 km and about 600,000 with diameters larger than 1 km.
If the L5 swarm contains a comparable number of objects, there are more than 1 million Jupiter trojans 1 km in size or larger. For the objects brighter than absolute magnitude 9.0 the population is complete. These numbers are similar to that of comparable asteroids in the asteroid belt; the total mass of the Jupiter trojans is estimated at 0.0001 of the mass of Earth or one-fifth of the mass of the asteroid belt. Two more recent studies indicate that the above numbers may overestimate the number of Jupiter trojans by several-fold; this overestimate is caused by the assumption that all Jupiter trojans have a low albedo of about 0.04, whereas small bodies may have an average albedo as high as 0.12. According to the new estimates, the total number of Jupiter trojans with a diameter larger than 2 km is 6,300 ± 1,000 and 3,400 ± 500 in the L4 and L5 swarms, respectively; these numbers would be reduced by a factor of 2 if small Jupiter trojans are more reflective than large ones. The number of Jupiter trojans observed in the L4
A trans-Neptunian object written transneptunian object, is any minor planet in the Solar System that orbits the Sun at a greater average distance than Neptune, which has a semi-major axis of 30.1 astronomical units. TNOs are further divided into the classical and resonant objects of the Kuiper belt, the scattered disc and detached objects with the sednoids being the most distant ones; as of October 2018, the catalog of minor planets contains 528 numbered and more than 2,000 unnumbered TNOs. The first trans-Neptunian object to be discovered was Pluto in 1930, it took until 1992 to discover a second trans-Neptunian object orbiting the Sun directly, 15760 Albion. The most massive TNO known is Eris, followed by Pluto, 2007 Makemake and Haumea. More than 80 satellites have been discovered in orbit of trans-Neptunian objects. TNOs vary in color and are either grey-blue or red, they are thought to be composed of mixtures of rock, amorphous carbon and volatile ices such as water and methane, coated with tholins and other organic compounds.
Twelve minor planets with a semi-major axis greater than 150 AU and perihelion greater than 30 AU are known, which are called extreme trans-Neptunian objects. The orbit of each of the planets is affected by the gravitational influences of the other planets. Discrepancies in the early 1900s between the observed and expected orbits of Uranus and Neptune suggested that there were one or more additional planets beyond Neptune; the search for these led to the discovery of Pluto in February 1930, too small to explain the discrepancies. Revised estimates of Neptune's mass from the Voyager 2 flyby in 1989 showed that the problem was spurious. Pluto was easiest to find because it has the highest apparent magnitude of all known trans-Neptunian objects, it has a lower inclination to the ecliptic than most other large TNOs. After Pluto's discovery, American astronomer Clyde Tombaugh continued searching for some years for similar objects, but found none. For a long time, no one searched for other TNOs as it was believed that Pluto, which up to August 2006 was classified a planet, was the only major object beyond Neptune.
Only after the 1992 discovery of a second TNO, 15760 Albion, did systematic searches for further such objects begin. A broad strip of the sky around the ecliptic was photographed and digitally evaluated for moving objects. Hundreds of TNOs were found, with diameters in the range of 50 to 2,500 kilometers. Eris, the most massive TNO, was discovered in 2005, revisiting a long-running dispute within the scientific community over the classification of large TNOs, whether objects like Pluto can be considered planets. Pluto and Eris were classified as dwarf planets by the International Astronomical Union. On Monday, December 17, 2018 the discovery of 2018 VG18, nicknamed “Farout”, was announced. Farout is the most distant solar system object so-far observed and is about 120 AU away from the sun taking more than 1,000 years to complete one orbit. According to their distance from the Sun and their orbital parameters, TNOs are classified in two large groups: the Kuiper belt objects and the scattered disc objects.
The diagram to the right illustrates the distribution of known trans-Neptunian objects in relation to the orbits of the planets and the centaurs for reference. Different classes are represented in different colours. Resonant objects are plotted in classical Kuiper belt objects in blue; the scattered disc extends to the right, far beyond the diagram, with known objects at mean distances beyond 500 AU and aphelia beyond 1000 AU. The Edgeworth-Kuiper belt contains objects with an average distance to the Sun of 30 to about 55 AU having close-to-circular orbits with a small inclination from the ecliptic. Edgeworth-Kuiper belt objects are further classified into the resonant trans-Neptunian object, that are locked in an orbital resonance with Neptune, the classical Kuiper belt objects called "cubewanos", that have no such resonance, moving on circular orbits, unperturbed by Neptune. There are a large number of resonant subgroups, the largest being the twotinos and the plutinos, named after their most prominent member, Pluto.
Members of the classical Edgeworth-Kuiper belt include 50000 Quaoar and Makemake. The scattered disc contains objects farther from the Sun, with eccentric and inclined orbits; these orbits are non-planetary-orbit-crossing. A typical example is the most massive known Eris. Based on the Tisserand parameter relative to Neptune, the objects in the scattered disc can be further divided into the "typical" scattered disc objects with a TN of less than 3, into the detached objects with a TN greater than 3. In addition, detached objects have a time-averaged eccentricity greater than 0.2 The Sednoids are a further extreme sub-grouping of the detached objects with perihelia so distant that it is confirmed that their orbits cannot be explained by perturbations from the giant planets, nor by interaction with the galactic tides. Given the apparent magnitude of all but the biggest trans-Neptunian objects, the physical studies are limited to the following: thermal emissions for the largest objects colour indices, i.e. comparisons of the apparent magnitudes using different filters analysis of spectra and infraredStudying colours and spectra provides insight into the objects' origin and a potential correlation with other classes of objects, namely centaurs and some satellites of giant planets, suspected to originate in the Kuiper belt.
The term apsis refers to an extreme point in the orbit of an object. It denotes either the respective distance of the bodies; the word comes via Latin from Greek, there denoting a whole orbit, is cognate with apse. Except for the theoretical possibility of one common circular orbit for two bodies of equal mass at diametral positions, there are two apsides for any elliptic orbit, named with the prefixes peri- and ap-/apo-, added in reference to the body being orbited. All periodic orbits are, according to Newton's Laws of motion, ellipses: either the two individual ellipses of both bodies, with the center of mass of this two-body system at the one common focus of the ellipses, or the orbital ellipses, with one body taken as fixed at one focus, the other body orbiting this focus. All these ellipses share a straight line, the line of apsides, that contains their major axes, the foci, the vertices, thus the periapsis and the apoapsis; the major axis of the orbital ellipse is the distance of the apsides, when taken as points on the orbit, or their sum, when taken as distances.
The major axes of the individual ellipses around the barycenter the contributions to the major axis of the orbital ellipses are inverse proportional to the masses of the bodies, i.e. a bigger mass implies a smaller axis/contribution. Only when one mass is sufficiently larger than the other, the individual ellipse of the smaller body around the barycenter comprises the individual ellipse of the larger body as shown in the second figure. For remarkable asymmetry, the barycenter of the two bodies may lie well within the bigger body, e.g. the Earth–Moon barycenter is about 75% of the way from Earth's center to its surface. If the smaller mass is negligible compared to the larger the orbital parameters are independent of the smaller mass. For general orbits, the terms periapsis and apoapsis are used. Pericenter and apocenter are equivalent alternatives, referring explicitly to the respective points on the orbits, whereas periapsis and apoapsis may refer to the smallest and largest distances of the orbiter and its host.
For a body orbiting the Sun, the point of least distance is the perihelion, the point of greatest distance is the aphelion. The terms become apastron when discussing orbits around other stars. For any satellite of Earth, including the Moon, the point of least distance is the perigee and greatest distance the apogee, from Ancient Greek Γῆ, "land" or "earth". For objects in lunar orbit, the point of least distance is sometimes called the pericynthion and the greatest distance the apocynthion. Perilune and apolune are used. In orbital mechanics, the apsides technically refer to the distance measured between the barycenters of the central body and orbiting body. However, in the case of a spacecraft, the terms are used to refer to the orbital altitude of the spacecraft above the surface of the central body; these formulae characterize the pericenter and apocenter of an orbit: Pericenter Maximum speed, v per = μ a, at minimum distance, r per = a. Apocenter Minimum speed, v ap = μ a, at maximum distance, r ap = a.
While, in accordance with Kepler's laws of planetary motion and the conservation of energy, these two quantities are constant for a given orbit: Specific relative angular momentum h = μ a Specific orbital energy ε = − μ 2 a where: a is the semi-major axis: a = r per + r ap 2 μ is the standard gravitational parameter e is the eccentricity, defined as e = r ap − r per r ap + r per = 1 − 2 r ap r per + 1 Note t
An hour is a unit of time conventionally reckoned as 1⁄24 of a day and scientifically reckoned as 3,599–3,601 seconds, depending on conditions. The hour was established in the ancient Near East as a variable measure of 1⁄12 of the night or daytime; such seasonal, temporal, or unequal hours varied by latitude. The hour was subsequently divided into each of 60 seconds. Equal or equinoctial hours were taken as 1⁄24 of the day. Since this unit was not constant due to long term variations in the Earth's rotation, the hour was separated from the Earth's rotation and defined in terms of the atomic or physical second. In the modern metric system, hours are an accepted unit of time defined as 3,600 atomic seconds. However, on rare occasions an hour may incorporate a positive or negative leap second, making it last 3,599 or 3,601 seconds, in order to keep it within 0.9 seconds of UT1, based on measurements of the mean solar day. The modern English word hour is a development of the Anglo-Norman houre and Middle English ure, first attested in the 13th century.
It displaced the Old English "tide" and "stound". The Anglo-Norman term was a borrowing of Old French ure, a variant of ore, which derived from Latin hōra and Greek hṓrā. Like Old English tīd and stund, hṓrā was a vaguer word for any span of time, including seasons and years, its Proto-Indo-European root has been reconstructed as *yeh₁-, making hour distantly cognate with year. The time of day is expressed in English in terms of hours. Whole hours on a 12-hour clock are expressed using the contracted phrase o'clock, from the older of clock. Hours on a 24-hour clock are expressed as "hundred" or "hundred hours". Fifteen and thirty minutes past the hour is expressed as "a quarter past" or "after" and "half past" from their fraction of the hour. Fifteen minutes before the hour may be expressed as "a quarter to", "of", "till", or "before" the hour; the ancient Egyptians began dividing the night into wnwt at some time before the compilation of the Dynasty V Pyramid Texts in the 24th century BC. By 2150 BC, diagrams of stars inside Egyptian coffin lids—variously known as "diagonal calendars" or "star clocks"—attest that there were 12 of these.
Clagett writes that it is "certain" this duodecimal division of the night followed the adoption of the Egyptian civil calendar placed c. 2800 BC on the basis of analyses of the Sothic cycle, but a lunar calendar long predated this and would have had twelve months in each of its years. The coffin diagrams show that the Egyptians took note of the heliacal risings of 36 stars or constellations, one for each of the ten-day "weeks" of their civil calendar; each night, the rising of eleven of these decans were noted, separating the night into twelve divisions whose middle terms would have lasted about 40 minutes each. The original decans used by the Egyptians would have fallen noticeably out of their proper places over a span of several centuries. By the time of Amenhotep III, the priests at Karnak were using water clocks to determine the hours; these were filled to the brim at sunset and the hour determined by comparing the water level against one of its twelve gauges, one for each month of the year.
During the New Kingdom, another system of decans was used, made up of 24 stars over the course of the year and 12 within any one night. The division of the day into 12 hours was accomplished by sundials marked with ten equal divisions; the morning and evening periods when the sundials failed to note time were observed as the first and last hours. The Egyptian hours were connected both with the priesthood of the gods and with their divine services. By the New Kingdom, each hour was conceived as a specific region of the sky or underworld through which Ra's solar barge travelled. Protective deities were used as the names of the hours; as the protectors and resurrectors of the sun, the goddesses of the night hours were considered to hold power over all lifespans and thus became part of Egyptian funerary rituals. Two fire-spitting cobras were said to guard the gates of each hour of the underworld, Wadjet and the rearing cobra were sometimes referenced as wnwt from their role protecting the dead through these gates.
The Egyptian for astronomer, used as a synonym for priest, was wnwty, "One of the Hours" or "Hour-Watcher". The earliest forms of wnwt include one or three stars, with the solar hours including the determinative hieroglyph for "sun". Ancient China divided its day into 100 "marks" running from midnight to midnight; the system is said to have been used since remote antiquity, credited to the legendary Yellow Emperor, but is first attested in Han-era water clocks and in the 2nd-century history of that dynasty. It was measured with sundials and water clocks. Into the Eastern Han, the Chinese measured their day schematically, adding the 20-ke difference between the solstices evenly throughout the year, one every nine days. During the night, time was more commonly
La Plata is the capital city of Buenos Aires Province, Argentina. According to the 2001 census, it has a population of 765,378 and its metropolitan area has 899,523 inhabitants. La Plata was planned and developed to serve as the provincial capital after the city of Buenos Aires was federalized in 1880, it was founded by Governor Dardo Rocha on 19 November 1882. Its construction is documented in photographs by Tomás Bradley Sutton. La Plata was known as Ciudad Eva Perón between 1952 and 1955; the city is home to two important first division football teams: Estudiantes de La Plata and Gimnasia y Esgrima La Plata. Rocha decided to erect a new city to host the provincial government institutions and a university, planned. Urban planner Pedro Benoit designed a city layout based on a rationalist conception of urban centers; the city has the shape of a square with a central park and two main diagonal avenues, north to south and east to west. In addition, there are numerous other shorter diagonal streets.
This design is copied in a self-similar manner in small blocks of six by six blocks in length. For every six blocks, there is square. Other than the diagonal streets, all streets are on a rectangular grid and are numbered consecutively. Thus, La Plata is nicknamed "la ciudad de las diagonales", it is called "la ciudad de los tilos", because of the large number of linden trees lining the many streets and squares. The linden tree is one of a number of deciduous Northern Hemisphere tree species which dominate La Plata's parks and streets. Palms and subtropical broadleaf evergreen trees are comparatively infrequent; the city design and its buildings are noted to possess a strong Freemason symbolism. This is said to be a consequence of both Benoit being Freemasons; the designs for the government buildings were chosen in an international architectural competition. Thus, the Governor Palace was designed by the City Hall by Germans, etc.. Electric street lighting was installed in 1884, was the first of its kind in Latin America.
The neo-Gothic cathedral of La Plata is the largest church in Argentina. The Teatro Argentino de La Plata is one of the most important opera houses in Argentina, second to the Teatro Colón in Buenos Aires; the theatre was built on 51st and 53rd Avenue. It was opened on 19 November 1890, it was designed by Leopoldo Rochi in Renaissance style. The work was funded by the first inhabitants of La Plata, but as maintenance was expensive, it was donated to the Province of Buenos Aires. In the foyer, entering through the majestic doors, there was a beautiful white Carrara marble staircase. In the concert hall, hangs a huge chandelier with trimmings suspended from the ceiling; the easy chairs were tapestried in blue velveteen and the Bordeaux curtain was embroidered in gold. It had marvelous acoustics. In those years, the students of the Verdi Conservatory of Music performed in the theatre, their annual show of classical Spanish and folklore dances with the teachers Carmen de Toledo, Mrs Schubert and Nelly Rossotti respectively.
Surrounding the theatre was the "Peace Garden," containing flags and national flowers of several countries. People strolled and children played along its stony paths. However, fate decreed; this has been noted as one of the largest losses to La Plata's historical heritage. It was replaced by a new building, which houses the theatre's orchestra and ballet, boasting several halls; the Curutchet House is one of the two buildings by Le Corbusier built in the Americas. The University of La Plata was founded in 1897 and nationalized in 1905, it is well known for natural history museum. Ernesto Sabato graduated in Physics at this university. Doctor René Favaloro was another famous alumnus. During its early years, the university attracted a number of renowned intellectuals from the Spanish-speaking world, such as Dominican Pedro Henríquez Ureña. San Ponciano church is situated on the corner of 5th Streets, it was the first chapel in La Plata, inaugurated on 19 November 1883, on the first anniversary of the foundation of the city.
The project belongs to Pedro Benoit, the designer of the city plan. Its neogothic style has been well kept and the inner paintings are now being restored; the founder of the city, Dardo Rocha, named it "San Ponciano" in memory of Ponciano. St. Ponciano was born in Rome. In 230 he was elected as Bishop of Pope; because of the Christian Persecution he was forced into exile to the unhealthy Sardinia Island. In 235 he resigned his position as pope because he did not want to leave the Church in a difficult situation during his absence, he was buried in the catacombs of Saint Callixtus among eight other Popes. Inside the church, you can see the authentic "Virgen de Luján" niche, moved here in 1904.- Under Alvear's administration, Enrique Mosconi, the president of the oil state company Yacimientos Petrolíferos Fiscales, created the distillery of La Plata, the tenth largest in the world. On 10 December 1945, in the Parish church of St. Francis of Assisi in this city, Juan Domingo Perón and Eva Duarte got married.
The city was renamed in 1952 as Eva Perón, though its original name was restored in 1955. Several daily newspapers are published there, the most prominent of, El Día. In October 1998, UNESCO approved the city's bid to gain recogni
The asteroid belt is the circumstellar disc in the Solar System located between the orbits of the planets Mars and Jupiter. It is occupied by numerous irregularly shaped bodies called minor planets; the asteroid belt is termed the main asteroid belt or main belt to distinguish it from other asteroid populations in the Solar System such as near-Earth asteroids and trojan asteroids. About half the mass of the belt is contained in the four largest asteroids: Ceres, Vesta and Hygiea; the total mass of the asteroid belt is 4% that of the Moon, or 22% that of Pluto, twice that of Pluto's moon Charon. Ceres, the asteroid belt's only dwarf planet, is about 950 km in diameter, whereas 4 Vesta, 2 Pallas, 10 Hygiea have mean diameters of less than 600 km; the remaining bodies range down to the size of a dust particle. The asteroid material is so thinly distributed that numerous unmanned spacecraft have traversed it without incident. Nonetheless, collisions between large asteroids do occur, these can produce an asteroid family whose members have similar orbital characteristics and compositions.
Individual asteroids within the asteroid belt are categorized by their spectra, with most falling into three basic groups: carbonaceous and metal-rich. The asteroid belt formed from the primordial solar nebula as a group of planetesimals. Planetesimals are the smaller precursors of the protoplanets. Between Mars and Jupiter, gravitational perturbations from Jupiter imbued the protoplanets with too much orbital energy for them to accrete into a planet. Collisions became too violent, instead of fusing together, the planetesimals and most of the protoplanets shattered; as a result, 99.9% of the asteroid belt's original mass was lost in the first 100 million years of the Solar System's history. Some fragments found their way into the inner Solar System, leading to meteorite impacts with the inner planets. Asteroid orbits continue to be appreciably perturbed whenever their period of revolution about the Sun forms an orbital resonance with Jupiter. At these orbital distances, a Kirkwood gap occurs. Classes of small Solar System bodies in other regions are the near-Earth objects, the centaurs, the Kuiper belt objects, the scattered disc objects, the sednoids, the Oort cloud objects.
On 22 January 2014, ESA scientists reported the detection, for the first definitive time, of water vapor on Ceres, the largest object in the asteroid belt. The detection was made by using the far-infrared abilities of the Herschel Space Observatory; the finding was unexpected because comets, not asteroids, are considered to "sprout jets and plumes". According to one of the scientists, "The lines are becoming more and more blurred between comets and asteroids." In 1596, Johannes Kepler predicted “Between Mars and Jupiter, I place a planet” in his Mysterium Cosmographicum. While analyzing Tycho Brahe's data, Kepler thought that there was too large a gap between the orbits of Mars and Jupiter. In an anonymous footnote to his 1766 translation of Charles Bonnet's Contemplation de la Nature, the astronomer Johann Daniel Titius of Wittenberg noted an apparent pattern in the layout of the planets. If one began a numerical sequence at 0 included 3, 6, 12, 24, 48, etc. doubling each time, added four to each number and divided by 10, this produced a remarkably close approximation to the radii of the orbits of the known planets as measured in astronomical units provided one allowed for a "missing planet" between the orbits of Mars and Jupiter.
In his footnote, Titius declared "But should the Lord Architect have left that space empty? Not at all."When William Herschel discovered Uranus in 1781, the planet's orbit matched the law perfectly, leading astronomers to conclude that there had to be a planet between the orbits of Mars and Jupiter. On January 1, 1801, Giuseppe Piazzi, chair of astronomy at the University of Palermo, found a tiny moving object in an orbit with the radius predicted by this pattern, he dubbed it "Ceres", after the Roman goddess of the patron of Sicily. Piazzi believed it to be a comet, but its lack of a coma suggested it was a planet. Thus, the aforementioned pattern, now known as the Titius–Bode law, predicted the semi-major axes of all eight planets of the time. Fifteen months Heinrich Olbers discovered a second object in the same region, Pallas. Unlike the other known planets and Pallas remained points of light under the highest telescope magnifications instead of resolving into discs. Apart from their rapid movement, they appeared indistinguishable from stars.
Accordingly, in 1802, William Herschel suggested they be placed into a separate category, named "asteroids", after the Greek asteroeides, meaning "star-like". Upon completing a series of observations of Ceres and Pallas, he concluded, Neither the appellation of planets nor that of comets, can with any propriety of language be given to these two stars... They resemble small stars so much. From this, their asteroidal appearance, if I take my name, call them Asteroids. By 1807, further investigation revealed two new objects in the region: Vesta; the burning of Lilienthal in the Napoleonic wars, where the main body of work had been done, brought this first period of discovery to a close. Despite Herschel's coinage, for several decades it remained common practice to refer to these objects as planets and to prefix t