According to Space.com:
Sunspots are darker, cooler areas on the surface of the sun in a region called the photosphere.
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.
Pretty cool, right?
They are, but they can also cause catastrophic danger, which is one of the reasons that NASA’s latest find has scientists concerned.
NASA has spotted (no pun intended) a massive sunspot that experts fear could cause radio blackouts, knock out communication satellites, and create radiation storms.
Close Up Of The 75,000-Mile Wide Sunspot
The sunspot, which is 74,560 miles wide, has been named AR2665 and is big enough to be seen from Earth.