Spectrum (physical sciences)

In the <a href="/facts/Physical_sciences/30ztjEKK">physical sciences</a>, the term spectrum was introduced first into <a href="/facts/Optics/p0vq4S1T">optics</a> by <a href="/facts/Isaac_Newton/4L7gTncN">Isaac Newton</a> in the 17th century, referring to the range of colors observed when white light was <a href="/facts/Dispersion_(optics)/cUdHnYXz">dispersed</a> through a <a href="/facts/Prism_(optics)/eodBFF70">prism</a>. 
Soon the term referred to a plot of light <a href="/facts/Intensity_(physics)/KFWkJkJI">intensity</a> or <a href="/facts/Power_(physics)/mkaEyRnn">power</a> as a function of <a href="/facts/Frequency/QUSbPaW8">frequency</a> or <a href="/facts/Wavelength/kcJU0ymz">wavelength</a>, also known as a <a href="/facts/Spectral_density/q3Rfs7b0">spectral density</a> plot.
Later it expanded to apply to other <a href="/facts/Wave/fU0HH6St">waves</a>, such as <a href="/facts/Sound_wave/DlKXlPuF">sound waves</a> and <a href="/facts/Sea_wave/7IsEqwJp">sea waves</a> that could also be measured as a function of frequency (e.g., <a href="/facts/Noise_spectrum/q2v4WmXe">noise spectrum</a>, <a href="/facts/Sea_wave_spectrum/7IsEqwJp">sea wave spectrum</a>). It has also been expanded to more abstract "<a href="/facts/Signal/41YqUJ8c">signals</a>", whose <a href="/facts/Power_spectrum/q3Rfs7b0">power spectrum</a> can be <a href="/facts/Spectrum_analyzer/MatIRUbR">analyzed</a> and <a href="/facts/Signal_processing/Npaja6zb">processed</a>. The term now applies to any signal that can be measured or decomposed along a continuous variable, such as energy in <a href="/facts/Electron_spectroscopy/4SFmzqjX">electron spectroscopy</a> or mass-to-charge ratio in <a href="/facts/Mass_spectrometry/RH5WBHJ2">mass spectrometry</a>. Spectrum is also used to refer to a graphical representation of the signal as a function of the dependent variable.

Spectrum (physical sciences) open-in-new

Spectrum (physical sciences)