It was a quiet day on the Sun in September of 2000. The above image from NASA's sun-observing TRACE spacecraft shows, however, that even during "off days" the Sun's surface is a busy place. Shown in ultraviolet light, the relatively cool dark regions have temperatures of thousands of degrees.
A large sunspot group is visible as the bright area near the horizon. The bright glowing gas flowing around the sunspots has a temperature of over one million degrees Celsius (1.8 million degrees Fahrenheit). The high temperatures are thought to be related to the rapidly changing magnetic field loops that channel solar plasma.
