Illustration of the spectrum of sunlight, with absorption lines (vertical), drawn by the German physicist Joseph von Fraunhofer (1787-1826). The spectrum ranges from blue (right) to red (left). The absorption lines, known as Fraunhofer lines, indicate the presence of certain elements in the Sun's atmosphere and were discovered by Fraunhofer in 1814. The curve at top shows the intensity of sunlight in different parts of the spectrum as perceived by the human eye. From Determination of the Refractive and Dispersive Indices of Differing Types of Glass in Relation to the Perfection of Achromatic Telescopes (1817).