Large sunspots on the sun. SOHO image, On March 30, 2001, the sunspot area within the group spanned an area more than 13 times the entire surface of the Earth. It was the source of numerous flares and coronal mass ejections, including the largest flare recorded in 25 years on April 2, 2001. Caused by intense magnetic fields emerging from the interior, a sunspot appears to be dark only when contrasted against the rest of the solar surface, because it is slightly cooler than the unmarked regions.