Electromagnetic spectrum
<p >The <b>electromagnetic spectrum</b> is the <a href="http://en.wikipedia.org/wiki/Spectrum" title="Spectrum" >range</a> of all possible frequencies of <a href="http://en.wikipedia.org/wiki/Electromagnetic_radiation" title="Electromagnetic radiation" >electromagnetic radiation</a>.<sup id="cite_ref-0" class="reference" ><a href="http://en.wikipedia.org/wiki/Electromagnetic_spectrum#cite_note-0" >[1]</a></sup> </p>
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The "electromagnetic spectrum" of an object is the characteristic distribution of electromagnetic radiation emitted or absorbed by that particular object.</p>
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The electromagnetic spectrum extends from low frequencies used for modern <a href="http://en.wikipedia.org/wiki/Radio" title="Radio" >radio</a> communication to <a href="http://en.wikipedia.org/wiki/Gamma_radiation" title="Gamma radiation" class="mw-redirect" >gamma radiation</a> at the short-<a href="http://en.wikipedia.org/wiki/Wavelength" title="Wavelength" >wavelength</a> (high-frequency) end, thereby covering wavelengths from thousands of <a href="http://en.wikipedia.org/wiki/Kilometer" title="Kilometer" class="mw-redirect" >kilometers</a> down to a <a href="http://en.wikipedia.org/wiki/Fraction(mathematics)" title="Fraction (mathematics)" >fraction</a>of the size of an <a href="http://en.wikipedia.org/wiki/Atom" title="Atom" >atom</a>. It is for this reason that the electromagnetic spectrum is highly studied for spectroscopic purposes to characterize matter.<sup id="cite_ref-em-spectrum_1-0" class="reference" ><a href="http://en.wikipedia.org/wiki/Electromagnetic_spectrum#cite_note-em-spectrum-1" >[2]</a></sup> The limit for long wavelength is the size of the <a href="http://en.wikipedia.org/wiki/Universe" title="Universe" >universe</a> itself, while it is thought that the short wavelength limit is in the vicinity of the <a href="http://en.wikipedia.org/wiki/Planck_length" title="Planck length" >Planck length</a>,<sup id="cite_ref-2" class="reference" ><a href="http://en.wikipedia.org/wiki/Electromagnetic_spectrum#cite_note-2" >[3]</a></sup> although in principle the spectrum is <a href="http://en.wikipedia.org/wiki/Infinity" title="Infinity" >infinite</a> and <a href="http://en.wikipedia.org/wiki/Continuum(theory)" title="Continuum (theory)" >continuous</a>.</p>