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A shift of direction (or location) from the one predicted by a simple calculation. Abberation of starlight--a small shift in the observed position of stars, due to the Earth's orbital velocity.
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temperature in degrees centigrade (also known in this case as "degrees Kelvin" K°) measured from the absolute zero of -273.1° C, the temperature at which all atomic and molecular motions are expected to cease.
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Dark lines interrupting a continuous color spectrum, caused by a cool gas between the light source and the observer. Cool gas absorbs light in the same frequencies as it emits when hot, e.g. double yellow line of sodium. Such dark lines in the Sun's spectrum were discovered by Joseph Frauenhofer
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Rate at which velocity changes (negative acceleration--slowing down--is also known as deceleration). Acceleration is a vector quantity.
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A branch of mathematics. Originally (and still in high school context), it refers to the art of calculating with unknown quantities, represented by letters. Modern algebra has expanded this to manipulating symbols represented by letter, following certain rules which may differ from the ones applying to numbers, e.g. vector algebra, matrix algebra etc.
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A relation involving unknown numbers, which is satisfied only for a certain value (or values) of those numbers. Finding those values is "solving the equation."
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As used here, representing an algebraic expression involving a small quantity by a sum of terms which rapidly decrease. By omitting the small term, an approximate solution may be obtained. In an iteration, the procedure is repeated again and again, increasing the accuracy.
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A relation between undefined quantities, each representing a variable. For instance, after t seconds, the velocity v of a stone thrown vertically with velocity u is, in meters/second, (neglecting air resistance) v = g * t + u where * marks multiplication and g = 9.81 is the acceleration due to gravity. Unlike n equation, the formula has no specific solution: but if you replace g, t and u by the appropriate numbers, it will give the value of v.
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A relation between symbols (usually letters) representing unknown numbers, which is always correct, regardless of the numbers the symbols represent. For instance, if a^2 is the second power (a squared) and * denotes multiplication, then (a^2)-(b^2)=(a+b)*(a-b). Sometimes distinguished by replacing the ymbol = with one containing three parallel lines.
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in the theory of airplane wings, the angle between the wing profile (roughly, measured along its bottom) and the wing's motion relative to the surrounding air.
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in orbital motion, one of the angles which gauges the motion of a planet or satellite around its orbit, increasing by 360o every revolution. The true anomaly f equals the polar angle f in polar coordinates with origin at the center of the motion (e.g. Sun or Earth). The mean anomaly is a related angle which increases in direct proportion to the time elapsed (the true anomaly does not--the motion is faster near the center). The eccentric anomaly is an auxiliary angle used in relating true anomaly (which is observed) and mean anomaly (which is calculated).
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the point in a planet's orbit furthest from the Sun (Helios is Greek for Sun). See perihelion, apogee.
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the point in a satellite's orbit furthest away from Earth (see perigee, aphelion).
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the US mission to land humans on the Moon and bring them back safely.
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The observed motion of a heavenly body across the celestial sphere, assuming the Earth is at the sphere's center and is standing still.
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Mean Sun-Earth distance, used as scaling distance in the solar system. Using Kepler's laws, it is easy to derive distances in this system as measured in astronomical units. Independent measurement of one distance in that system then fixes the magnitude of all the rest.
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An early liquid-fueled rocket, used by US astronauts and still in use for unmanned launches. Because of its lightweight construction it uses no staging, but only drops two of its engines.
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Two angles which give the direction of a surveyor's telescope (theodolite). Azimuth is the rotation angle of the telescope around a vertical axis, measured (counterclockwise from above) from due north, a direction whose azimuth is zero degrees. Elevation is the angle the telescope is lifted above the horizontal plane.
[In 3-dimensional polar coordinates centered on the instrument, azimuth is f, elevation is 90o-q; the direction of straight up has elevation 90o but q = 0].
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