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Charles T. Kowal
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Charles Thomas Kowal was an American astronomer known for his observations and discoveries in the Solar System. He was awarded the James Craig Watson Medal for his contributions to astronomy in 1979, in the 1960s, Kowal observed with the Palomar 48 Schmidt telescope, contributing observations to noted cosmologist Fritz Zwickys six-volume Catalogue of Galaxies and of Clusters of Galaxies. In the course of these Palomar supernovae surveys with the 48 Schmidt, Kowal personally discovered 81 supernovae, although primarily employed by the supernova survey to observe on the 48 Schmidt, Kowal provided crucial observations of particularly faint asteroids for the PCAS program with the larger telescope. PCAS later moved to the 48 Schmidt, and ran in total for nearly 25 years, Kowal provided observations of new Solar System discoveries and reports of new supernovae via the IAU circular system throughout the 1970s, and searched for new objects. He discovered two moons of Jupiter, Leda in 1974 and Themisto in 1975, the 13th and 14th moons of Jupiter to be found, Themisto was later lost and was not rediscovered until 2000. Between December 1976 and February 1985, Kowal searched 6400 square degrees of sky in the plane for distant. Only one object was found beyond Jupiter,2060 Chiron, discovered in 1977 and it became recognised as the first object in the centaur class after a second one was discovered 15 years later. Centaurs are objects with unstable orbits which orbit between Jupiter and Neptune and they are probably drawn in from the Kuiper belt by alignments with larger planets. Chiron remains one of the largest such worlds known, and one of a handful that have a comet-like coma, Kowal also discovered or co-discovered the periodic comets 99P/Kowal, 104P/Kowal, 134P/Kowal-Vavrova, 143P/Kowal-Mrkos, and 158P/Kowal-LINEAR. Kowal moved to the new Space Telescope Science Institute in 1985 and his book Asteroids, Their Nature and Utilization was published in 1988, and a second edition in 1996. Kowal died on November 28,2011 at the age of 71, Kowal was awarded the National Academy of Sciences James Craig Watson Medal for his noteworthy astronomical discoveries, particularly of Chiron, Leda, and numerous supernovae in 1979. The crater Kowal on Pluto was named in his honor

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Apsis
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An apsis is an extreme point in an objects orbit. The word comes via Latin from Greek and is cognate with apse, for elliptic orbits about a larger body, there are two apsides, named with the prefixes peri- and ap-, or apo- added to a reference to the thing being orbited. For a body orbiting the Sun, the point of least distance is the perihelion, the terms become periastron and apastron when discussing orbits around other stars. For any satellite of Earth including the Moon the point of least distance is the perigee, for objects in Lunar orbit, the point of least distance is the pericynthion and the greatest distance the apocynthion. For any orbits around a center of mass, there are the terms pericenter and apocenter, periapsis and apoapsis are equivalent alternatives. A straight line connecting the pericenter and apocenter is the line of apsides and this is the major axis of the ellipse, its greatest diameter. For a two-body system the center of mass of the lies on this line at one of the two foci of the ellipse. When one body is larger than the other it may be taken to be at this focus. Historically, in systems, apsides were measured from the center of the Earth. In orbital mechanics, the apsis technically refers to the distance measured between the centers of mass of the central and orbiting body. However, in the case of spacecraft, the family of terms are used to refer to the orbital altitude of the spacecraft from the surface of the central body. The arithmetic mean of the two limiting distances is the length of the axis a. The geometric mean of the two distances is the length of the semi-minor axis b, the geometric mean of the two limiting speeds is −2 ε = μ a which is the speed of a body in a circular orbit whose radius is a. The words pericenter and apocenter are often seen, although periapsis/apoapsis are preferred in technical usage, various related terms are used for other celestial objects. The -gee, -helion and -astron and -galacticon forms are used in the astronomical literature when referring to the Earth, Sun, stars. The suffix -jove is occasionally used for Jupiter, while -saturnium has very rarely used in the last 50 years for Saturn. The -gee form is used as a generic closest approach to planet term instead of specifically applying to the Earth. During the Apollo program, the terms pericynthion and apocynthion were used when referring to the Moon, regarding black holes, the term peri/apomelasma was used by physicist Geoffrey A. Landis in 1998 before peri/aponigricon appeared in the scientific literature in 2002

3.
Astronomical unit
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The astronomical unit is a unit of length, roughly the distance from Earth to the Sun. However, that varies as Earth orbits the Sun, from a maximum to a minimum. Originally conceived as the average of Earths aphelion and perihelion, it is now defined as exactly 149597870700 metres, the astronomical unit is used primarily as a convenient yardstick for measuring distances within the Solar System or around other stars. However, it is also a component in the definition of another unit of astronomical length. A variety of symbols and abbreviations have been in use for the astronomical unit. In a 1976 resolution, the International Astronomical Union used the symbol A for the astronomical unit, in 2006, the International Bureau of Weights and Measures recommended ua as the symbol for the unit. In 2012, the IAU, noting that various symbols are presently in use for the astronomical unit, in the 2014 revision of the SI Brochure, the BIPM used the unit symbol au. In ISO 80000-3, the symbol of the unit is ua. Earths orbit around the Sun is an ellipse, the semi-major axis of this ellipse is defined to be half of the straight line segment that joins the aphelion and perihelion. The centre of the sun lies on this line segment. In addition, it mapped out exactly the largest straight-line distance that Earth traverses over the course of a year, knowing Earths shift and a stars shift enabled the stars distance to be calculated. But all measurements are subject to some degree of error or uncertainty, improvements in precision have always been a key to improving astronomical understanding. Improving measurements were continually checked and cross-checked by means of our understanding of the laws of celestial mechanics, the expected positions and distances of objects at an established time are calculated from these laws, and assembled into a collection of data called an ephemeris. NASAs Jet Propulsion Laboratory provides one of several ephemeris computation services, in 1976, in order to establish a yet more precise measure for the astronomical unit, the IAU formally adopted a new definition. Equivalently, by definition, one AU is the radius of an unperturbed circular Newtonian orbit about the sun of a particle having infinitesimal mass. As with all measurements, these rely on measuring the time taken for photons to be reflected from an object. However, for precision the calculations require adjustment for such as the motions of the probe. In addition, the measurement of the time itself must be translated to a scale that accounts for relativistic time dilation