Absorption and Emission

When a photon with exactly the right energy hits an electron, the electron absorbs it and jumps to a higher energy level. The atom has just absorbed light. But excited electrons are unstable — within nanoseconds they fall back down and release a photon of the same energy.

This selective absorption is the basis of spectroscopy. Because every element absorbs its own set of wavelengths, each one leaves a unique spectral fingerprint that scientists use to identify what distant stars and everyday materials are made of.