Here is a close up view of sunspot AR3315, with a rough scaled image of the Earth to show the shear size of this grouping. Sunspots are cooler areas on the surface of the sun with the dark central dark umbra reaching approx. 4500 Celsius compared to the rest of the surface, which is approx. 6000 Celsius. It only appears darker as it is so much cooler. If it was on its own it would shine incredibly bright.