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Part II Key Themes and Major Figures

A narrow feature at a particular wavelength in the spectrum of electromagnetic radiation emitted by an object; it indicates that much less energy is being received at that wavelength than at others. Absorption lines are usually produced by a particular atomic process, such as when an electron jumps from one energy state to another, higher state. Since, according to quantum physics, these states occur only at discrete levels, the electron needs to absorb a photon of a specific wavelength in order to perform the jump.