I was the first instrument to clearly show that the energy from the sun is not a constant value but instead varies over time. These energy changes are small but significant and they cycle approximately every 11 years. The sun produces energy by converting hydrogen to helium in a process called nuclear fusion. Sunspots are a feature of the Sun that have been observed since ancient times. When viewed through a telescope, they have a dark central region known as the umbra, surrounded by a somewhat lighter region called the penumbra.
Sunspots are dark because they are cooler than the surrounding photosphere.
They are the site of strong magnetic fields. The reason sunspots are cool is not entirely understood, but one possibility is that the magnetic field in the spots inhibits convection underneath them. Sunspots typically grow over a few days and last anywhere from a few days to a few months. The number of sunspots on the Sun is not constant. While the cycle has been relatively uniform this century, there have been large variations in the past.