What Are Sunspots?

Sunspots are dark areas of irregular shape on the surface of the Sun. Sunspots are are cooler (~ 3000 degrees C) than the rest of the sun's surface (~ 6000 degrees C) and therefore appear dark. The spots last from a few days to a few months. Sunspots can be quite small (1500 km diameter), and reach sizes up to 50,000 km. The sharpness of the boundaries between the umbra and penumbra, and between the penumbra and photosphere, is a phenomenon that is not yet properly understood. While sunspots, especially large ones, can be fairly long-lived, they do eventually disappear, often by successive fragmentation into smaller and smaller sunspots. Likewise, sunspots do not suddenly appear fully grown, but usually show up as small structures, irregularly shaped and usually without a penumbra (darker structures without penumbra are usually referred to as pores).