An emission spectrum is a spectrum of the electromagnetic radiation emitted by a source. When atoms or molecules absorb energy, their electrons become excited and move to higher energy levels. When these electrons return to their original levels, they release energy in the form of light, producing specific wavelengths that appear as bright lines on a dark background. Each element has a unique emission spectrum, which acts like a fingerprint for that element. This property allows scientists to identify the composition of distant stars and galaxies by analyzing the light they emit, using tools like spectroscopes to observe these patterns.