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.

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 per second, measured in watts per square meter.

energy level

A particular level of energy possessed by an atom or ion above its least energetic state.

excitation

The process of giving an atom or an ion an amount of energy greater than it has in its lowest energy state.

frequency

The number of waves that cross a given point per unit time in radiation.

gamma rays

Photons 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 10^3–10^6 nanometers.

inverse square law

The amount of energy flowing through a given area decreases in proportion to the square of the distance from the source.

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

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.

nucleus (of an atom)

The massive part of an atom, composed mostly of protons and neutrons.

photon

A discrete unit of electromagnetic energy.

radial velocity

Motion toward or away from the observer.

radio waves

All electromagnetic waves longer than microwaves, including radar waves and AM radio waves.

spectrometer

An instrument for obtaining a spectrum, usually attached to a telescope in astronomy.

Stefan-Boltzmann law

A formula used to compute the rate at which a blackbody radiates energy.

ultraviolet

Electromagnetic radiation of wavelengths 10 to 400 nanometers.

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 it emits at the greatest intensity.

X-rays

Electromagnetic radiation with wavelengths between 0.01 and 20 nanometers.