The electric currents in the Sun, as well as in planets and galaxies, generate magnetic fields. Sunspots, temporary disturbances in the Sun’s photosphere, are the most visible advertisement of the solar magnetic field. They appear dark because temperatures are considerably lower than in surrounding areas. Sunspots occur where the magnetic field lines emerge from the inside of the Sun to form expanding loops above its surface.
Sunspots usually show up as small forms that are irregularly shaped, and grow within days or weeks to their full size. While they can last weeks or months, they do eventually disappear, often by breaking into smaller and smaller sunspots.