When the Sun is viewed through a solar telescope dark spots can be observed on the surface. These spots appear dark to the eye because they are cooler than the surrounding gas although they are still quite hot! The photosphere has a temperature of about 5500 degrees Celsius and a typical sunspot has a temperature about 3900 degrees Celsius.
A sunspot's lifetime can be as short as an hour or two or as long as several months. The number of sunspots that can be seen on the surface of the Sun increases and decreases in a regular pattern, known as the solar cycle, with a maximum number of sunspots occurring every 11 years.
Image Credit: Lockheed Martin Palo Alto Research Lab