Sunspot
The first cyclic changes of sunspots was seen by Heinrich Schwabe, and made Rudolf Wolf study them carefully, starting in 1848. Also in 1848, Joseph Henry showed a picture of the Sun and made sure that sunspots were cooler than the rest of the Sun (they are about 7000 degrees Fahrenheit, 4000 C). They are still very hot, but much cooler than the rest of the Sun's surface.