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absorption spectrum
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a series or pattern of dark lines superimposed on a continuous spectrum
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blackbody
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an idealized object that absorbs all electromagnetic energy that falls onto it
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continuous spectrum
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a spectrum of light composed of radiation of a continuous range of wavelengths or colors, rather than only certain discrete wavelengths
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dispersion
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separation of different wavelengths of white light through refraction of different amounts
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Doppler effect
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the apparent change in wavelength or frequency of the radiation from a source due to its relative motion away from or toward the observer
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electromagnetic radiation
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radiation consisting of waves propagated through regularly varying electric and magnetic fields and traveling at the speed of light
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electromagnetic spectrum
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the whole array or family of electromagnetic waves, from radio to gamma rays
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emission spectrum
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a series or pattern of bright lines superimposed on a continuous spectrum
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energy flux
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the amount of energy passing through a unit area (for example, 1 square meter) per second; the units of flux are watts per square meter
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energy level
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a particular level, or amount, of energy possessed by an atom or ion above the energy it possesses in its least energetic state; also used to refer to the states of energy an electron can have in an atom
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excitation
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the process of giving an atom or an ion an amount of energy greater than it has in its lowest energy (ground) state
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frequency
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the number of waves that cross a given point per unit time (in radiation)
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gamma rays
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photons (of electromagnetic radiation) of energy with wavelengths no longer than 0.01 nanometer; the most energetic form of electromagnetic radiation
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ground state
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the lowest energy state of an atom
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infrared
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electromagnetic radiation of wavelength 10
3
–10
6
nanometers; longer than the longest (red) wavelengths that can be perceived by the eye, but shorter than radio wavelengths
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inverse square law
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(for light) the amount of energy (light) flowing through a given area in a given time decreases in proportion to the square of the distance from the source of energy or light
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ion
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an atom that has become electrically charged by the addition or loss of one or more electrons
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ionization
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the process by which an atom gains or loses electrons
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isotope
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any of two or more forms of the same element whose atoms have the same number of protons but different numbers of neutrons
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microwave
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electromagnetic radiation of wavelengths from 1 millimeter to 1 meter; longer than infrared but shorter than radio waves
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nucleus (of an atom)
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the massive part of an atom, composed mostly of protons and neutrons, and about which the electrons revolve
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photon
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a discrete unit (or “packet”) of electromagnetic energy
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radial velocity
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motion toward or away from the observer; the component of relative velocity that lies in the line of sight
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radio waves
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all electromagnetic waves longer than microwaves, including radar waves and AM radio waves
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spectrometer
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an instrument for obtaining a spectrum; in astronomy, usually attached to a telescope to record the spectrum of a star, galaxy, or other astronomical object
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Stefan-Boltzmann law
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a formula from which the rate at which a blackbody radiates energy can be computed; the total rate of energy emission from a unit area of a blackbody is proportional to the fourth power of its absolute temperature:
F
= σ
T
4
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ultraviolet
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electromagnetic radiation of wavelengths 10 to 400 nanometers; shorter than the shortest visible wavelengths
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visible light
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electromagnetic radiation with wavelengths of roughly 400–700 nanometers; visible to the human eye
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wavelength
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the distance from crest to crest or trough to trough in a wave
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Wien’s law
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formula that relates the temperature of a blackbody to the wavelength at which it emits the greatest intensity of radiation
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X-rays
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electromagnetic radiation with wavelengths between 0.01 nanometer and 20 nanometers; intermediate between those of ultraviolet radiation and gamma rays