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This page is a glossary of astronomy. This scientific study is concerned with celestial objects and phenomena that originate outside the atmosphere of Earth. The field of astronomy has an extensive vocabulary and a significant amount of jargon. ==A== * Absolute magnitude is a measure of a star's absolute brightness. It is defined as the apparent magnitude the star would show if it were located at a distance of 10 parsecs, or 32.6 light years. * Accretion disk is a roughly circular mass of diffuse material in orbit around a central object, such as a star or black hole. The material has been acquired from a source external to the central object. * Albedo feature is a large area on the surface of a reflecting object that shows a contrast in brightness or darkness (albedo) with adjacent areas. * Am star is a chemically peculiar star belonging to the more general class of A-type stars. The spectrum of the Am stars shows abnormal enhancements and deficiencies of certain metals. (See metallicity below.) * Apoapsis is the point of furthest excursion, or separation, between two orbiting objects. * Apparent magnitude is a measure of the brightness of a celestial body as seen by an observer on Earth, adjusted to the value it would have in the absence of the atmosphere. The brighter the object appears, the lower the value of its magnitude. * Asterism is a pattern of stars recognized on Earth's night sky. It may form part of an official constellation, or be composed of stars from more than one. * Astrometric binary is a type of binary system where evidence for an unseen orbiting companion is revealed by its periodic gravitational perturbation of the visible component. See also spectroscopic binary. * Astronomical unit, or AU, is the approximate distance between the midpoints of the Earth and the Sun. * Autumnal equinox is the point in the year when the Sun appears to cross the celestial equator, while generally trending southward at each zenith passage. It represents the moment when the North Pole of the Earth begins to tilt away from the Sun. * Azimuth is an angular measurement of an object's orientation along the horizon of the observer, relative to the direction of true north. When combined with the altitude above the horizon, it defines an object's current position in the spherical coordinate system. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Glossary of astronomy」の詳細全文を読む スポンサード リンク
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