Radiation and spectra

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