Colour print of close-ups of the visible surface of the Sun, 1872.

One of eight colour lithographs (Pl.14) with window mounts of four colour sketches showing sunspots in white light, drawn by Etienne Leopold Trouvelot in 1872. Figure 1, April 20th, 10h 00m; Figure 2, April 25th 11h 00m; Figure 3, April 26th 09h 30m; Figure 4, July 5th, 09h 30m;

Lithographic colour print issued by Harvard College Observatory in 1876, showing close-ups of the solar photosphere, the visible surface of the Sun. Based on sketches made Etienne Leopold Trouvelot (1827-1895), a French artist, they show the appearance sunspots in white light on four dates during 1872. These black markings with a dark (umbra) surrounded by a lighter region (penumbra) are areas of cooler gas on the Sun's surface. With a dazzlingly bright surface and a temperature of over six thousand degrees centigrade their darkness is a contrast effects. The number of sunspots slowly increases to a maximum and then falls back in a clear 11-year cycle first recognised by the German astronomer Heinrich Schwabe in 1843.