The effects of the sun's internal magnetic fields entering and re-entering the surface of the sun result in sunspots. They typically occur in pairs with magnetic fields pointing in opposite directions.
The magnetic field around a sunspot is approximately 2,500 times stronger than Earth's magnetic field. The strong magnetic field creates a great magnetic pressure while the surrounding atmospheric pressure decreases. The umbra is the dark part of the sunspot. Its temperature is 6,000 degrees Fahrenheit while the surrounding surface of the sun reaches 10,000 degrees Fahrenheit, resulting in the dark color of the sunspot. Ultraviolet radiation greatly increases when sunspot activity is high, affecting Earth's atmosphere.
Coronal flares and solar mass injections occur near sunspots at the dividing line between areas of magnetic fields facing opposite directions. When sunspot activity is high, Earth experiences an increase in the northern and southern lights. This increase in solar flares and geomagnetic storms can also affect radio transmissions and Earth's power grid. The NASA/Marshall Space Flight Center makes predictions on sunspot activity by creating charts of solar cycles. From 1645 to 1715, the sun experienced a level of near zero sunspots called the Maunder Minimum. During this time, the "Little Ice Age" occurred in parts of Earth.