Secchi's sunspot observation. Artwork of an observation of a sunspot, made in 1873 by the Italian Jesuit astronomer Father Pietro Angelo Secchi (1818-1878). Sunspots, first observed with telescopes in 1610, are areas of magnetic activity that are cooler than the rest of the Sun's surface. They are massive structures, ranging in size from hundreds to thousands of kilometres across. This artwork shows the cooler central area (dark) and the hotter (lighter) areas round the sunspot.