Glossary term: Spectrum

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Description: The variation in intensity of light from a source as a function of wavelength or frequency is called a spectrum. When the variation of light across wavelengths is relatively smooth, it is called a continuous spectrum. On the other hand, there could be sharp dips or peaks in the spectrum; these are called absorption and emission lines, respectively. These lines arise mainly due to transitions of electrons within atoms: either absorbing or emitting radiation. Stars usually show absorption lines in their optical spectra which are superposed on continuum emission. The lines give important clues about the chemical composition of stars. The analysis of spectra is known as spectroscopy; instruments that allow for the recording of spectra are called spectroscopes, spectrometers or spectrographs.

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The OAE Multilingual Glossary is a project of the IAU Office of Astronomy for Education (OAE) in collaboration with the IAU Office of Astronomy Outreach (OAO). The terms and definitions were chosen, written and reviewed by a collective effort from the OAE, the OAE Centers and Nodes, the OAE National Astronomy Education Coordinators (NAECs) and other volunteers. You can find a full list of credits here. All glossary terms and their definitions are released under a Creative Commons CC BY-4.0 license and should be credited to "IAU OAE".