- absorption spectrum
- a series or pattern of dark lines superimposed on a continuous spectrum
- blackbody
- an idealized object that absorbs all electromagnetic energy that falls onto it
- continuous spectrum
- a spectrum of light composed of radiation of a continuous range of wavelengths or colors, rather than only certain discrete wavelengths
- dispersion
- separation of different wavelengths of white light through refraction of different amounts
- Doppler effect
- the apparent change in wavelength or frequency of the radiation from a source due to its relative motion away from or toward the observer
- electromagnetic radiation
- radiation consisting of waves propagated through regularly varying electric and magnetic fields and traveling at the speed of light
- electromagnetic spectrum
- the whole array or family of electromagnetic waves, from radio to gamma rays
- emission spectrum
- a series or pattern of bright lines superimposed on a continuous spectrum
- energy flux
- 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
- energy level
- 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
- excitation
- the process of giving an atom or an ion an amount of energy greater than it has in its lowest energy (ground) state
- frequency
- the number of waves that cross a given point per unit time (in radiation)
- gamma rays
- photons (of electromagnetic radiation) of energy with wavelengths no longer than 0.01 nanometer; the most energetic form of electromagnetic radiation
- ground state
- the lowest energy state of an atom
- infrared
- electromagnetic radiation of wavelength 103–106 nanometers; longer than the longest (red) wavelengths that can be perceived by the eye, but shorter than radio wavelengths
- inverse square law
- (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
- ion
- an atom that has become electrically charged by the addition or loss of one or more electrons
- ionization
- the process by which an atom gains or loses electrons
- isotope
- any of two or more forms of the same element whose atoms have the same number of protons but different numbers of neutrons
- microwave
- electromagnetic radiation of wavelengths from 1 millimeter to 1 meter; longer than infrared but shorter than radio waves
- nucleus (of an atom)
- the massive part of an atom, composed mostly of protons and neutrons, and about which the electrons revolve
- photon
- a discrete unit (or “packet”) of electromagnetic energy
- radial velocity
- motion toward or away from the observer; the component of relative velocity that lies in the line of sight
- radio waves
- all electromagnetic waves longer than microwaves, including radar waves and AM radio waves
- spectrometer
- 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
- Stefan-Boltzmann law
- 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 = σT4
- ultraviolet
- electromagnetic radiation of wavelengths 10 to 400 nanometers; shorter than the shortest visible wavelengths
- visible light
- electromagnetic radiation with wavelengths of roughly 400–700 nanometers; visible to the human eye
- wavelength
- the distance from crest to crest or trough to trough in a wave
- Wien’s law
- formula that relates the temperature of a blackbody to the wavelength at which it emits the greatest intensity of radiation
- X-rays
- electromagnetic radiation with wavelengths between 0.01 nanometer and 20 nanometers; intermediate between those of ultraviolet radiation and gamma rays