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Hal Levison
Harold F. (Hal) Levison (born 1959) is an American planetary scientist specializing in planetary dynamics. He currently works at the Southwest Research Institute, Boulder, Colorado, and studies planetary orbits and their evolution through Solar System history. Levison is the Principal Investigator of the ''Lucy'' mission to tour multiple Jupiter trojans, which was selected as the thirteenth mission in NASA's Discovery Program in January 2017. Among other achievements, Levison is the co-author of SWIFT, a commonly used symplectic integrator that solves planetary equations of motion for periods of billions of years. Levison argued for a distinction between what are now called dwarf planets and the other eight planet A planet is a large, rounded astronomical body that is neither a star nor its remnant. The best available theory of planet formation is the nebular hypothesis, which posits that an interstellar cloud collapses out of a nebula to create a you ...s based on t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Philadelphia, Pennsylvania
Philadelphia, often called Philly, is the largest city in the Commonwealth of Pennsylvania, the sixth-largest city in the U.S., the second-largest city in both the Northeast megalopolis and Mid-Atlantic regions after New York City. Since 1854, the city has been coextensive with Philadelphia County, the most populous county in Pennsylvania and the urban core of the Delaware Valley, the nation's seventh-largest and one of world's largest metropolitan regions, with 6.245 million residents . The city's population at the 2020 census was 1,603,797, and over 56 million people live within of Philadelphia. Philadelphia was founded in 1682 by William Penn, an English Quaker. The city served as capital of the Pennsylvania Colony during the British colonial era and went on to play a historic and vital role as the central meeting place for the nation's founding fathers whose plans and actions in Philadelphia ultimately inspired the American Revolution and the nation's inde ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
SWIFT (scientific Software)
Swift or SWIFT most commonly refers to: * SWIFT, an international organization facilitating transactions between banks ** SWIFT code * Swift (programming language) * Swift (bird), a family of birds It may also refer to: Organizations * SWIFT, an international organization facilitating transactions between banks * Swift Engineering, an American engineering firm * Swift & Company, a meat processing company * Swifts (aerobatic team), a Russian aerobatic team Transportation companies * Swift Cooper, a British racing car manufacturer * Swift Leisure, a British manufacturer of caravans * Swift Motor Company, of Coventry, England * Swift Transportation, a US trucking company Places * River Swift, a river in England * Swift, Illinois, an unincorporated community in northeastern Illinois * Swift County, Minnesota, a county in west-central Minnesota * Swift, Minnesota, an unincorporated community in northern Minnesota * Swift, Missouri, a ghost town in southeastern Missouri Astronomy ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Planetary Scientists
Planetary means relating to a planet or planets. It can also refer to: ;Science * Planetary habitability, the measure of an astronomical body's potential to develop and sustain life * Planetary nebula, an astronomical object ;People * Planetary (rapper), one half of east coast rap group OuterSpace ;Arts, entertainment, and media * ''Planetary'' (comics), a comic book series by Warren Ellis and John Cassaday * "Planetary (Go!)", a 2011 song by rock band My Chemical Romance * ''Planetary Radio'', a public radio show about space exploration, produced by The Planetary Society ;Organizations * The Planetary Society, the Earth's largest space interest group ;Technology * Epicyclic gearing (planetary gearing), an automotive transmission technology * Planetary scanner A planetary scanner (also called an orbital scanner) is a type of image scanner for making scans of rare books and other easily damaged documents. In essence, such a scanner is a mounted camera taking photos of a well- ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Clearing The Neighbourhood
"Clearing the neighbourhood" (or dynamical dominance) around a celestial body's orbit describes the body becoming gravitationally dominant such that there are no other bodies of comparable size other than its natural satellites or those otherwise under its gravitational influence. "Clearing the neighbourhood" is one of three necessary criteria for a celestial body to be considered a planet in the Solar System, according to the definition adopted in 2006 by the International Astronomical Union (IAU). In 2015, a proposal was made to extend the definition to exoplanets. In the end stages of planet formation, a planet, as so defined, will have "cleared the neighbourhood" of its own orbital zone, i.e. removed other bodies of comparable size. A large body that meets the other criteria for a planet but has not cleared its neighbourhood is classified as a dwarf planet. This includes Pluto, whose orbit intersects with Neptune's orbit and shares its orbital neighbourhood with many Kuiper ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Planet
A planet is a large, rounded astronomical body that is neither a star nor its remnant. The best available theory of planet formation is the nebular hypothesis, which posits that an interstellar cloud collapses out of a nebula to create a young protostar orbited by a protoplanetary disk. Planets grow in this disk by the gradual accumulation of material driven by gravity, a process called accretion. The Solar System has at least eight planets: the terrestrial planets Mercury, Venus, Earth and Mars, and the giant planets Jupiter, Saturn, Uranus and Neptune. These planets each rotate around an axis tilted with respect to its orbital pole. All of them possess an atmosphere, although that of Mercury is tenuous, and some share such features as ice caps, seasons, volcanism, hurricanes, tectonics, and even hydrology. Apart from Venus and Mars, the Solar System planets generate magnetic fields, and all except Venus and Mercury have natural satellites. The giant planets bear plan ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Dwarf Planet
A dwarf planet is a small planetary-mass object that is in direct orbit of the Sun, smaller than any of the eight classical planets but still a world in its own right. The prototypical dwarf planet is Pluto. The interest of dwarf planets to planetary geologists is that they may be geologically active bodies, an expectation that was borne out in 2015 by the ''Dawn'' mission to and the '' New Horizons'' mission to Pluto. Astronomers are in general agreement that at least the nine largest candidates are dwarf planets: Pluto, , , , , , , , and . Of these and the tenth-largest candidate , all but Sedna have either been visited by spacecraft (Pluto and Ceres) or have at least one known moon (Pluto, Eris, Haumea, Makemake, Gonggong, Quaoar, Orcus, and Salacia), which allows their masses and thus an estimate of their densities to be determined. Mass and density in turn can be fit into geophysical models in an attempt to determine the nature of these worlds. Some astronomers include ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Billion
Billion is a word for a large number, and it has two distinct definitions: *1,000,000,000, i.e. one thousand million, or (ten to the ninth power), as defined on the short scale. This is its only current meaning in English. * 1,000,000,000,000, i.e. one million million, or (ten to the twelfth power), as defined on the long scale. This number, which is one thousand times larger than the short scale billion, is now referred to in English as one trillion. However, this number is the historical meaning in English for the word "billion" (with the exception of the United States), a meaning was still in official use in British English until some time after World War II. American English adopted the short scale definition from the French (it enjoyed usage in France at the time, alongside the long-scale definition). The United Kingdom used the long scale billion until 1974, when the government officially switched to the short scale, but since the 1950s the short scale had already been incre ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Equations Of Motion
In physics, equations of motion are equations that describe the behavior of a physical system in terms of its motion as a function of time.''Encyclopaedia of Physics'' (second Edition), R.G. Lerner, G.L. Trigg, VHC Publishers, 1991, ISBN (Verlagsgesellschaft) 3-527-26954-1 (VHC Inc.) 0-89573-752-3 More specifically, the equations of motion describe the behavior of a physical system as a set of mathematical functions in terms of dynamic variables. These variables are usually spatial coordinates and time, but may include momentum components. The most general choice are generalized coordinates which can be any convenient variables characteristic of the physical system.''Analytical Mechanics'', L.N. Hand, J.D. Finch, Cambridge University Press, 2008, The functions are defined in a Euclidean space in classical mechanics, but are replaced by curved spaces in relativity. If the dynamics of a system is known, the equations are the solutions for the differential equations describi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Symplectic Geometry
Symplectic geometry is a branch of differential geometry and differential topology that studies symplectic manifolds; that is, differentiable manifolds equipped with a closed differential form, closed, nondegenerate form, nondegenerate differential form, 2-form. Symplectic geometry has its origins in the Hamiltonian mechanics, Hamiltonian formulation of classical mechanics where the phase space of certain classical systems takes on the structure of a symplectic manifold. The term "symplectic", introduced by Weyl, is a calque of "complex"; previously, the "symplectic group" had been called the "line complex group". "Complex" comes from the Latin ''com-plexus'', meaning "braided together" (co- + plexus), while symplectic comes from the corresponding Greek ''sym-plektikos'' (συμπλεκτικός); in both cases the stem comes from the Indo-European root wiktionary:Reconstruction:Proto-Indo-European/pleḱ-, *pleḱ- The name reflects the deep connections between complex and sym ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
United States
The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country primarily located in North America. It consists of 50 states, a federal district, five major unincorporated territories, nine Minor Outlying Islands, and 326 Indian reservations. The United States is also in free association with three Pacific Island sovereign states: the Federated States of Micronesia, the Marshall Islands, and the Republic of Palau. It is the world's third-largest country by both land and total area. It shares land borders with Canada to its north and with Mexico to its south and has maritime borders with the Bahamas, Cuba, Russia, and other nations. With a population of over 333 million, it is the most populous country in the Americas and the third most populous in the world. The national capital of the United States is Washington, D.C. and its most populous city and principal financial center is New York City. Paleo-Americ ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Jupiter Trojan
The Jupiter trojans, commonly called trojan asteroids or simply 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 stable Lagrange points: either ', existing 60° ahead of the planet in its orbit, or ', 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. More than 9,800 Jupiter trojans have been found . 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 , approximately equal to the number of asteroids larger than 1 km in the asteroid belt. Like main-belt asteroids, Jupiter trojans form families. , man ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
