The images from cameras and sensors on the latest satellite watching the sun are a dramatic reminder of the awesome power of the star that warms our planet. They show clouds of magnetized gas big enough to engulf the Earth breaking away from the outermost layer of the sun's atmosphere. These coronal mass ejections (CMEs), which are usually accompanied by solar flares with the explosive force of millions of atomic bombs, can last for several hours and travel through space at over 1 million kilometers per hour. Yet the sun has been in one of its quietest recorded phases for a century. The sun's activity ebbs and flows in a cycle that averages about 11 years.
Sunspots, vast dark areas on the sun created by strong magnetic fields beneath its surface, provide a visual guide to the evolution of the solar cycle, appearing in large numbers at the time of maximum activity and all but disappearing during the minimum.
NASA launched its Solar Dynamics Observatory satellite in February not just to gain a better understanding of how the sun behaves and why, but also to keep a closer watch on space weather.