Final answer:
Sunspots are dark because they are cooler than their surroundings, with a large sunspot center typically around 3800 K compared to the photosphere's 5800 K.
Step-by-step explanation:
Sunspots appear dark because they are cooler than the surrounding areas of the Sun. This cooler region results in a diminished brightness compared to the hotter, brighter photosphere that surrounds them. Sunspots, though cooler and thus darker, are still incredibly hot, in fact hotter than the surfaces of many stars. If sunspots were isolated from the Sun and observed separately, they would be quite luminous, shining as bright as the full moon in the night sky. The temperature at the center of a large sunspot is typically about 3800 K, while the surrounding photosphere has a temperature of approximately 5800 K.