Sunspots consist of a central dark area called umbra, and an outer brighter ring named penumbra with a filamentary appearance. While the umbra has strong vertical magnetic fields, the penumbra has weaker fields which bend until they are nearly horizontal. Sunspots can be observed in many different sizes and shapes, from round to elongated, and from a size of a few thousand km to monster sunspots of up to 100 000 km of diameter. They can last days, weeks, or even several months.