From time immemorial, the sun has been part of numerous legends and myths. Beyond these myths, ancient cultures have recognized the sun as crucial to life on Earth. Many ancient astronomers have observed it, trying to understand and record its unique features.
As early as 28 B.C., astronomers in ancient China, recorded systematic observations of small, changing dark patches on the surface of the sun. And there are some early references to such dark patches in the writings of Greek philosophers from the fourth century BC.
Scientists today call these patches sunspots. What are sunspots ?
Sunspots are places on the Sun that are cooler than the rest of the Sun's surface. The sunspot is relatively cool because convective motion of the gas, i.e.the movement of gas, which brings new, hot, gas to the surface, is reduced in these areas of the Sun. .Because they are cooler, they appear darker. They are only dark in a relative sense; a sunspot removed from the bright background of the Sun would glow quite brightly .
Sunspots can be much larger in diameter than Earth. They often come in groups. They form in a few days and usually disappear within weeks. Some large spots, though, may last for months. Sunspots are roughly circular. They have a dark center called the umbra and a less dark outer region called the penumbra.
Sunspots are linked to magnetic activity on the Sun. Sunspots are magnetic regions on the Sun with magnetic field strengths thousands of times stronger than the Earth's magnetic field. This strong magnetic field inhibits convection of heat to the surface- leading to the "dark" spots. The average number of visible sunspots varies over time, increasing and decreasing on a regular cycle of between 9.5 to 11 years, on average about 10.8 years. . This is called a solar cycle. During the cycle, the period when the spots are maximum is called solar maximum and when the spots are minimum it is called solar minimum. The number of sunspots is an indication of how active the Sun is. The Sun is said to be "quiet" at solar minimum.