Over the span of 11 years, the Sun’s activity waxes and wanes as magnetic field lines that are wound and tangled inside the Sun periodically break through to the surface. These breakthroughs produce a pair of sunspots of opposite magnetic polarity, one positive and the other negative, that travel together across the face of the Sun. The heightened magnetic activity associated with sunspots can lead to solar flares, coronal mass ejections, and other far-reaching electromagnetic phenomena that endanger astronauts and damage or disrupt satellites.

This series of images from the Solar and Heliospheric Observatory (SOHO) spacecraft shows sunspots (right) and ultraviolet light (left) emitted by the Sun each April 29 from 1999 through 2009. A smattering of sunspots darkened the visible surface of the Sun on March 29, 1999 (right), while observations of ultraviolet light (left) revealed how the magnetic activity that produced the sunspots excited the overlying solar atmosphere, producing an intensely bright spot. As Solar Cycle 23 reached its peak between 2000-2002, numerous sunspots speckled both hemispheres, and then their numbers dramatically dropped off as the cycle went toward its minimum.

If you map the location of the spots on the Sun’s surface over the course of a solar cycle, the pattern they make is shaped like a butterfly. The reason for the butterfly pattern is that the first sunspots of each new solar cycle occur mostly at the Sun’s mid-latitudes, but as the solar cycle progresses, the area of maximum sunspot production shifts toward the (solar) equator.

Solar Cycle 24 began in early 2008, but showed minimal activity through early 2009. Although the final image in this series—from April 29, 2009—does show a pair of small sunspots (far right, most visible in large image), the location of the spots near the equator mean that they belong to solar cycle 23, and not the new cycle. Solar cycle 24 has been unusually slow to ramp up.

The small changes in solar irradiance that occur during the solar cycle exert a small influence on Earth’s climate, with periods of intense magnetic activity (the solar maximum) producing slightly higher temperatures, and solar minimum periods such as that seen in 2008 and early 2009 likely to have the opposite effect.