Galileo and other astronomers first observed dark spots on the sun in 1610. These dark spots that they saw are now called sunspots.
Sunspots are in areas located on the surface of the sun that are cooler than the surrounding areas.
In 1843 German astronomer Samuel Heinrich Schwabe announced that there was a pattern to the number of sunspots he had observed. Schwabe made observations everyday the sun was visible for seventeen years and found that there were about ten years between the highest numbers of sunspots he observed. It was this discovery that founded the study of solar physics and remains the foundation for what we call the solar cycle today. Later the rotation of the sun was measured by observing the movements of the sunspots. British astronomer Richard Christopher Carrington in 1859 discovered that the sun did not rotate as one body and therefore was gaseous.