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Electromagnetic spectrum

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The electromagnetic (EM) spectrum is the range of all possible electromagnetic radiation. Electromagnetic radiation can be divided into octaves — as sound waves are — adding up to eighty-one octaves.[1] Physicists have studied electromagnetic radiation with wavelengths from thousands of kilometres down to fractions of the size of an atom. It is commonly said that EM waves beyond these limits are uncommon, although this is not known to be true. The short wavelength limit is likely to be the Planck length, and the long wavelength limit is the size of the universe itself, though in principle the spectrum is infinite.

Electromagnetic spectrum

Spectra of objects

Nearly all objects in the universe emit, reflect or transmit some light. (One hypothetical exception may be dark matter.) The distribution of this light along the electromagnetic spectrum (called the spectrum of the object) is determined by the object's composition. Several types of spectra can be distinguished depending upon the nature of the radiation coming from an object.

Spectroscopy is the branch of physics that studies matter by its emitted or reflected spectra.

NOTE: The AUDIO entry in this graphic is there for comparison only. Sound waves and light are two different things entirely.


  1. Isaac Asimov, Isaac Asimov's Book of Facts. Hastingshouse/Daytrips Publ., 1992. Page 389.

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