When scientists first began observing the spectrum of light reaching Earth from the Sun, the spectrum contained many dark lines, which indicated that light of certain wavelengths wasn’t present in the sunlight. These are now called Fraunhofer lines (named after their discoverer), and they are caused by the elements in the outer atmosphere of the Sun absorbing certain wavelengths of light, which prevents those wavelengths from reaching the Earth. Understanding that Fraunhofer lines were caused by atomic absorptions was one of the earliest examples of atomic spectroscopy.