During periods of peak activity (front three images) sunspots, solar flares and coronal mass ejections are more common, and the Sun emits slightly more energy than during periods of low activity (back images). The amount of energy that strikes Earth’s atmosphere -- called total solar irradiance (TSI) -- fluctuates by about 0.1 percent over the course of the Sun's 11-year cycle, even though the soft X-ray wavelengths shown in this image vary by much greater amounts. Credit: Steele Hill, SOHO, NASA/ESA