![]() ![]() If the atmospheric lapse rate is less than the adiabatic lapse rate, the rising blob will decelerate, and convective motion is prevented. If the atmospheric lapse rate (the decrease in temperature with increasing altitude in the surrounding atmosphere) is greater than the adiabatic lapse rate, the rising blob will accelerate, and convective motion is supported. This produces crystalline mineral structures which are physically and chemically distinct from meteorites which never underwent such melting and crystallization.Īchromat - A lens made of two pieces of glass (or, occasionally, other materials) with differing optical properties, specifically chosen to minimize chromatic aberration.Īdiabatic lapse rate - The rate at which temperature decreases as a rising blob of gas expands, to match the decreasing pressure around it. Achondrites are pieces broken off of parent bodies which were large enough to melt and differentiate, then slowly resolidify. In the planetesimal accretion theory, the earliest stages of this process involve random collisions, while the later stages involve random collisions aided by gravitational attraction.Īchondrite (literally, not a chondrite) - A stony meteorite which is not a chondrite, and does not contain chondrules. In the case of a star, the gases may be in the atmosphere, or at the surface of the star, in which case they reveal the physical conditions in those regions (but also see interstellar absorption lines).Īccretion - A process of growth in which small things become large things through collisions. Because this is a fixed distance, it is a measure of the star's intrinsic, or actual, brightness (also see apparent magnitude).Ībsorption lines - Dark lines in the spectrum of an object, caused by the absorption of light by gases lying between us and that object. Aberration - One of a number of optical distortions produced by an optical instrument, caused not by a defect in the instrument, but by the nature of its design, and the laws of optical physics (e.g., see chromatic aberration).Īlso, a change in the apparent direction of a star, caused by that portion of the Earth's orbital velocity toward or away from the star (see stellar aberration).Ībsolute magnitude - A number specifying the brightness that a star would have if viewed from a distance of 10 parsecs, or 32.6 light-years. ![]()
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