Emission Spectrum Definition (Science)

The emission spectrum shows the relative abundance of photons at each wavelength of the electromagnetic spectrum.
The emission spectrum shows the relative abundance of photons at each wavelength of the electromagnetic spectrum. MirageC / Getty Images

In general, an emission spectrum describes the wavelengths of the electromagnetic spectrum emitted by an energetic object. What this object is depends on the scientific discipline.

In chemistry, an emission spectrum refers to the range of wavelengths emitted by an atom or compound stimulated by either heat or electric current. An emission spectrum is unique to each element. The emission spectrum of a burning fuel or other molecule may also be used to example its composition.

In astronomy, the emission spectrum generally refers to the spectrum of a star, nebula, or other body.

How an Emission Spectrum Is Produced

When an atom or molecule absorbs energy, electrons are bumped into a higher energy state. When the electron drops to a lower energy state, a photon is released equal to the energy between the two states. There are multiple energy states available to an electron, so there are many possible transitions, leading to the numerous wavelengths that comprise the emission spectrum. Because each element has a unique emission spectrum, the spectrum obtained from any hot or energetic body may be used to analyze its composition.