Absorption spectroscopy is a technique used to find out what makes up a sample of a substance – in other words, a chemical analysis.

When a full spectrum of light (light with all the colours, like light from the sun) passes through the sample (which is often a gas) some specific colours do not show up on the other side. These colours of light are being absorbed by the sample. An image is created of the spectrum of light with black breaks where the light has been absorbed. These breaks are called absorption lines, and every element has its characteristic pattern of absorption lines.