Dominique-François-Jean Arago (1786–1853) was the leading French astronomer for the first half of the nineteenth century. Among Arago’s achievements in astronomy is his discovery of the Sun’s chromosphere. He also offered a pioneering explanation for the twinkling of stars, and conducted research that helped lead one of his assistants, Urbain Jean Joseph Leverrier, to discover the planet Neptune. Arago made important contributions to the understanding of electromagnetism and optics as well.