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Dynamic Time
In time standards, dynamical time is the independent variable of the equations of celestial mechanics. This is in contrast to time scales such as mean solar time which are based on how far the earth has turned. Since Earth's rotation is not constant, using a time scale based on it for calculating the positions of heavenly objects gives errors. Dynamical time can be inferred from the observed position of an astronomical object via a theory of its motion. A first application of this concept of dynamical time was the definition of the ephemeris time scale (ET). at p.304 In the late 19th century it was suspected, and in the early 20th century it was established, that the rotation of the Earth (''i.e.'' the length of the day) was both irregular on short time scales, and was slowing down on longer time scales. The suggestion was made, that observation of the position of the Moon, Sun and planets and comparison of the observations with their gravitational ephemerides would be a bett ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Deviation Of Day Length From SI Day
Deviation may refer to: Mathematics and engineering * Allowance (engineering), an engineering and machining allowance is a planned deviation between an actual dimension and a nominal or theoretical dimension, or between an intermediate-stage dimension and an intended final dimension. * Deviation (statistics), the difference between the value of an observation and the mean of the population in mathematics and statistics ** Standard deviation, which is based on the square of the difference ** Absolute deviation, where the absolute value of the difference is used ** Relative standard deviation, in probability theory and statistics is the absolute value of the coefficient of variation * Deviation of a local ring in mathematics * Deviation of a poset in mathematics * Frequency deviation, the maximum allowed "distance" in FM radio from the nominal frequency a station broadcasts at * Magnetic deviation, the error induced in compasses by local magnetic fields Albums * ''Deviation'' ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Caesium
Caesium (IUPAC spelling; also spelled cesium in American English) is a chemical element; it has Symbol (chemistry), symbol Cs and atomic number 55. It is a soft, silvery-golden alkali metal with a melting point of , which makes it one of only five elemental metals that are liquid at or near room temperature. Caesium has physical and chemical properties similar to those of rubidium and potassium. It is pyrophoricity, pyrophoric and reacts with water even at . It is the least electronegativity, electronegative stable element, with a value of 0.79 on the Pauling scale. It has only one stable isotope, caesium-133. Caesium is mined mostly from pollucite. Caesium-137, a fission product, is extracted from waste produced by nuclear reactor technology, nuclear reactors. It has the largest atomic radius of all elements whose radii have been measured or calculated, at about 260 picometres. The German chemist Robert Bunsen and physicist Gustav Kirchhoff discovered caesium in 1860 by the new ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
