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30 Cards in this Set
- Front
- Back
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Aberration
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in optics, an imperfect focus caused when a mirror or lens fails to bring light to a sharp focus
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absolute magnitude
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the apparent brightness an object would have if it were 10 parsecs (32.6 light-years) from Earth
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absolute zero
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the coldest theoretical temperature, equal to 0 kelvin (-459.67° F or -273.15° C)
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absorption lines
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dark lines in a spectrum caused by the absorption of light by atoms or molecules in a star or planet’s atmosphere
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accretion disk
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a disk surrounding a black hole or star in which matter gravitationally falls onto the central object
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achromatic lens
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a two-element lens, or doublet, that significantly reduces chromatic aberration
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active galactic nuclei
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the exceptionally bright cores of some galaxies, thought to be fueled by matter falling into supermassive black holes
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active galaxy
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a galaxy emitting unusually large amounts of energy from a compact central source
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active optics
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The techniques by which corrections are made to the shape of a large mirror or radio dish to adjust for minute distortions in its shape. These variations arise as a telescope is subjected to forces such as gravity and temperature changes.
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adaptive optics
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a system of telescopes, computers, and deformable mirrors used to compensate for atmospheric blurring
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Airy disk
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the bright disk-like image of a point source of light, such as a star, as seen in an optical system with a circular aperture
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albedo
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the percentage of light that an object reflects
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altazimuth mount
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a mount that enables a telescope to move freely both vertically (in altitude) and horizontally (in azimuth)
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altitude
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1. the height above sea level
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anaglyph
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a stereoscopic, composite image in which the right component (usually red in color) is superimposed on the left component (usually blue) to produce a three dimensional effect when viewed through correspondingly colored filters
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Andromeda Galaxy
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the largest member of the Local Group of galaxies; roughly twice the size of the Milky Way; also known as M31
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angular size
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the apparent width of an object as seen by an observer, usually expressed in degrees, arcminutes, or arcseconds
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anisotropies
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differences in physical properties depending on direction
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anisotropy
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the variation of a physical property depending on direction
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annular eclipse
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a solar eclipse in which the moon does not fully cover the sun’s disk, allowing observers to see a thin ring of sunlight
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antimatter
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matter consisting of particles that have the same mass and properties as their matter counterparts but opposite electrical charges
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anti-tail
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The name given to a comet's tail when it points toward the sun. This rare event typically occurs when Earth crosses the plane of the comet's orbit and the comet is relatively close to the sun.
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aperture
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the diameter of a telescope’s primary lens or mirror; the larger the aperture, the greater the telescope’s light-gathering power
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aphelion
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the point farthest from the sun in an object’s orbit
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apochromatic lens
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a lens with three or more elements that reduces chromatic aberration even more than an achromatic lens
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apogee
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the point in a satellite’s orbit when it is farthest from Earth
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Apollo
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1. the U.S. space program that sent astronauts to the moon in the 1960s and '70s2. an asteroid with a perihelion less than 1.017 AU (and thus comes within the orbit of Earth)
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apparent field of view
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the angular diameter of the circle of light that the eye sees through an eyepiece
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apparent magnitude
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the measure of the brightness of an object as seen from Earth
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apparition
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the period of time during which a particular celestial object can be seen
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