A sunspot will have a very dark central region known as the umbra. It is often surrounded by a less dark halo known as the penumbra. If they could be removed from the Sun, they would be seen to shine brightly. They appear dark only by contrast with the hotter, brighter surrounding photosphere. Spots change over a period of several days.
Individual sunspots have lifetimes that range from a few hours to a few months.
Many spots become much larger than the Earth, and a few have reached diameters of 50,000 km. Very few about 5 times this diameter. The improper use of telescopes or binoculars will cause blindness. There are safe and easy ways to safely observe the Sun. Incorrect observation of the Sun causes blindness because of the tremendous amount of visible and invisible light coming off of its surface.