"In 1814 Joseph von Fraunhofer, a German optician, used a spectroscope to produce a spectrum of the Sun. He noticed that the spectrum contained a number of dark lines on a continuous spectrum. Fraunhofer had no explanation for these dark lines, but it was later discovered that they had resulted from sunlight passing through cooler gases in the Sun's atmosphere. A dark-line spectrum, called an absorption spectrum, is like a jigsaw puzzle with a few missing pieces. All stars show this type of spectrum. "