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57 Cards in this Set

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Any measure of the intrinsic brightness or luminosity of a celestial object.
Absolute brightness
not dependent on the position or distance of the observer.
absolute intrinsic
The absolute brightness (luminosity) of a star expressed in the magnitude system. The Sun's absolute magnitude is +5.
Absolute magnitude
The microwave background radiation, or any group of objects whose overall motion is at rest with respect to the microwave background radiation. Neither the Milky Way nor the Local Group define an absolute reference frame.
Absolute reference frame
The temperature scale in which 0 = absolute zero, 273 = the freezing point of water, and 373 = the boiling point of water. The units are called Kelvins. One Kelvin = 1°C.
Absolute temperature scale
The loss of photons as light passes through a medium. A photon is lost when it strikes an electron, and the photon's energy is consumed in knocking the electron to a higher energy level.
A dark or dim region of the spectrum, caused by absorption of light over a moderate range of wavelengths, typically about 0.1 nm, usually by molecules or crystals.
Absorption band
In a spectrum, a reduction in intensity in a narrow interval of wavelength, caused by absorption of the light by atoms between the source and the observer.
Absorption line
The gradual accumulation of mass; usually refers to the building up of larger masses from stellar ones through the mutual gravitational attraction of matter.
A disk of hot gas and dust surrounding a star, usually used to denote material that has been thrown off one star onto a companion. There is weaker observational evidence for very large accretion disks in the central regions of active galaxies and quasars.
Accretion disck
A type of stony meteorite in which chondrules have been destroyed, probably by heating or melting.
A galaxy that has a more luminous centre than a normal galaxy. Galaxy whose nucleus emits more energy than other, normal galaxies. Typical signatures of active galaxies are variable brightness, broad emission lines, and strong radio emission.
Active Galaxy
About 12-16 billion years.
Age of Globular clusters
Time since formation of open clusters, judged by their H-R diagrams. Most are less than 100 million years. Ages from 1 million to a few billion years have been reported.
Age of Open Clusters
Time since star formation, typically billions of years for smaller stars, but less than a million years for some massive stars in recently formed clusters. Age is difficult to measure for individual stars, but possible to measure for clusters of stars.
Age of stars
Estimated to be roughly 12-16 billion years.
Age of the Milky Way Galaxy
The period since the Earth's formation from planetesimals, measured to be 4.6 billion years.
Age of the Earth
Visible and infrared glow from the atmosphere excited by solar radiation.
In the telescopic image of a star, a small disk caused by optical effects.
Airy disk
The research institution and collection of ancient works preserved after the fall of Rome at Alexandria, Egypt. Alexandrian knowledge passed to the Arabs with the Arab conquest of Alexandria, and eventually back into Europe around a.d. 100-1500.
Alexandrian Library
The nearest star system, composed of three members; (2) the brightest of these three.
Alpha Centauri (1)
Altitude (angular distance above the horizon) and Azimuth (compass direction expressed in angular measure).
Altazimuth Cooridiates
See altazimuth coordinates.
A complex organic molecule important in composing protein and called a building block of life.
Amino Acid
The nearest spiral galaxy comparable to our own, about 670 kpc away.
Andromeda galaxy
Abbreviated Å. A unit of length equal to 10-8 cm (one-hundredth of a millionth of a centimeter). An Angstrom is in the order of the size of an atom.
Any measure of the size or separation of two objects as seen from a specified point, expressed in angular units (degrees, minutes of arc, or seconds of arc), but not linear units (such as kilometers, miles, or parsecs).
Angular measure
The tendency of a body to keep rotating, unless acted upon by an outside force. Celestial objects that orbit or rotate possess this property.
Angular momentum
The angle subtended by an object at a given distance.
Angular size
Something that is not the same in every direction.
An eclipse in which the light source is almost, but not quite, covered, leaving a thin ring of light at mid-eclipse.
Annular solar eclipse
Material, with equivalent properties to matter, but with subatomic particles' quantum properties reversed; for example, particles' charges are opposite. Antimatter happens to be rare in our universe. Matter and antimatter annihilate on contact to produce gamma rays. -
The diameter of the light-gathering objective in a telescope.
The point in an orbit around the Earth that is farthest from the Earth.
Asteroids that cross the Earth's orbit.
Apollo asteroids
The U.S. program to land humans on the Moon, 1961-72; first landing July 20, 1969.
Apollo program
Not intrinsic, but dependent on the position or distance of an observer.
The brightness of an object as perceived by an observer at a specified location (but not measuring the object's intrinsic, or absolute, brightness).
Apparent brightness
Apparent brightness of one star relative to another as expressed in the magnitude system. --
Apparent magnitude
Time of day determined by the Sun's actual position in the sky. Apparent solar noon occurs as the Sun crosses the meridian. Apparent solar time is different at each different longitude.
Apparent solar time
The period of a few weeks during which a planet is most prominent or best placed for observation from Earth.
A unit of angular measure in which there are 360 arc degrees in a full circle.
Arc degree
Concentrations of particles along only a portion (less than 30°) of a circular ring around a planet, probably caused by gravitational forces associated with small nearby moonlets.
Arc rings
Abbreviated arcsec. A unit of angular measure in which there are 60 arc seconds in 1 arc minute and therefore 3600 arc seconds in 1 arc degree. One arc second is equal to about 725 km on the Sun.
Arc second
A loosely connected grouping of young stars.
A rocky or metallic interplanetary body (usually larger than 100 m in diameter).
The grouping of asteroids orbiting between Mars and Jupiter.
Asteroid belt
In a planetary body, a subsurface layer that is more plastic than adjacent layers because the combination of pressure and temperature places it near (or slightly above) the melting point. Asthenospheric movements may disrupt the planet's surface.
The superstitious belief that human lives are influenced or controlled by the positions of planets and stars; this belief is rejected by modern astronomers and other scientists.
A binary star system detectable from the orbital motion of a single visible component.
Astometric binary
The study of positions and motions of the stars.
The mean distance from the Earth to the Sun, about 150 million kilometers.
Astronomical unit (AU)
The study of all matter and energy in the universe.
A particle of matter composed of a nucleus surrounded by orbiting electrons.
The mean distance from the Earth to the Sun, about 150 million kilometers
Glowing, often moving colored light forms seen near the north and south magnetic polies of the Earth; caused by radiation from high-altitude air moliecules excited by particles from thje Sun and Van Allen belts.
Compass direction expressed in angular measure as opposed to altazimuth (angular distance above the horizon.)