Fraunhofer lines are dark lines that appear in the spectrum of sunlight when it is passed through a prism or diffraction grating. These lines are caused by the absorption of specific wavelengths of light by elements in the Sun's atmosphere, such as hydrogen, helium, and heavier elements. Each element absorbs light at characteristic wavelengths, creating a unique pattern of lines. Named after the German physicist Joseph von Fraunhofer, who studied them in the early 19th century, these lines provide valuable information about the composition and temperature of stars. By analyzing the Fraunhofer lines, scientists can identify the elements present in distant celestial bodies and understand their physical properties.