What is Sunspot?

 Sunspots are darker, cooler areas on the surface of the sun in a region called the photosphere.

A sunspot is basically a magnetic storm on the surface of a star, including our own sun. It results in a slightly cool area which looks darker than the surrounding solar atmosphere. These run in a 22 year cycle, with a minimum every 11 years, and then a magnetic reversal for the next 11 years. 

The photosphere has a temperature of 5,800 degrees Kelvin. Sunspots have temperatures of about 3,800 degrees K. They look dark only in comparison with the brighter and hotter regions of the photosphere around them.

Sunspots can be very large, up to 50,000 kilometers in diameter. They are caused by interactions with the Sun's magnetic field which are not fully understood. But a sunspot is somewhat like the cap on a soda bottle: shake it up, and you can generate a big eruption. Sunspots occur over regions of intense magnetic activity, and when that energy is released, solar flares and big storms called coronal mass ejections erupt from sunspots.

Image credit: Google