Sunspots are dark spots that migrate across the surface of the sun. Astronomers believe that the spots on the sun are actually electrical and magnetic. Sunspots appear to be whirlwinds of electrified matter bursting out from the sun's interior. They shoot beams of negatively charged electrons into space, some of which enter the earth's atmosphere. This can cause electromagnetic effects, such as the northern lights, or disrupt radio transmissions.
Sunspots are cooler than the rest of the sun's surface because less new, hot gas is brought to the surface in those areas. That's why they appear dark. They are roughly circular and have a dark center called the umbra. The less dark outer region is called the penumbra. There is also a region called a plage that is slightly brighter than the rest of the region. The plage emits cosmic rays, ultraviolet light, and X-rays, which are all related to visible light, but are much stronger.
Sunspots form within a few days, and usually disappear within a few weeks. They can vary in size, from small specks on the sun's surface, to regions as much as 90,000 miles long and 200,000 miles in length. They can even be larger across than the Earth is.
Sunspots follow a recurring 11-year cycle. Over this time, sunspots and solar flares get more frequent, then rarer. These times are called the solar maximum and the solar minimum.
Sunspots are visible on most clear days, but you should never look at the sun directly with the naked eye, or even through dark glasses. This can damage vision. To look for sunspots or other features on the sun, use a shaded telescope or specially designed eyewear to protect your eyes.