Sept 16, 2010
Scientists studying sunspots for the past 2 decades have concluded that the magnetic field that triggers their formation has been steadily declining.
If the current trend continues, by 2016 the sun’s face may become spotless and remain that way for decades—a phenomenon that in the 17th century coincided with a prolonged period of cooling on Earth.
Sunspots appear when upwellings of the sun’s magnetic field trap ionized plasma—or electrically charged, superheated gas—on the surface. Normally, the gas would release its heat and sink back below the surface, but the magnetic field inhibits this process. From Earth, the relatively cool surface gas looks like a dark blemish on the sun.
Astronomers have been observing and counting sunspots since Galileo began the practice in the early 17th century. From those studies, scientists have long known that the sun goes through an 11-year cycle, in which the number of sunspots spikes during a period called the solar maximum and drops—sometimes to zero—during a time of inactivity called the solar minimum.