Sunspots are dark, planet-size regions of strong magnetic fields on the surface of the sun. They appear as temporary spots that are darker than the surrounding areas and are regions of reduced surface temperature caused by concentrations of magnetic flux that inhibit convection. Sunspots tend to occur in pairs that have magnetic fields pointing in opposite directions, and a typical spot consists of a dark region called the umbra, surrounded by a lighter region known as the penumbra. The surrounding surface of the Sun (the photosphere) is about 10,000 degrees F, while the umbra is about 6,300 degrees F, which makes sunspots appear relatively dark.
Sunspots form when concentrations of magnetic field from deep within the sun well up to the surface, according to the European Solar Telescope. Although the details of sunspot formation are still a matter of ongoing research, it is widely understood that they are the visible manifestations of magnetic flux tubes in the Suns convective zone projecting through the photosphere within active regions. Sunspots are our window into the suns complicated magnetic interior, and they have fascinated solar observers for hundreds of years.
Sunspots are areas where the magnetic field is about 2,500 times stronger than Earths, much higher than anywhere else on the Sun. Because of the strong magnetic field, the magnetic pressure increases while the surrounding atmospheric pressure decreases. This, in turn, lowers the temperature relative to its surroundings because the concentrated magnetic field inhibits the flow of hot, new gas from the Suns interior to the surface.
Sunspots are important because they can spawn eruptive disturbances such as solar flares and coronal mass ejections (CMEs). The frequency and intensity of sunspots visible on the surface indicate the level of solar activity during the 11-year solar cycle that is driven by the suns magnetic field. Due to their correlation with other kinds of solar activity, sunspots can be used to help predict space weather, the state of the ionosphere, and conditions relevant to short-wave radio propagation or satellite communications.
