BOULDER, COLORADO—For all of February the sun is nearly spotless, a smooth circle filled in with a goldenrod crayon. It has been more than a decade since it was so lacking in sunspots—dark magnetic knots as big as Earth that are a barometer of the sun’s temperament. Below the surface, however, a radical transition is afoot. In 5 years or so, the sun will be awash in sunspots and more prone to violent bursts of magnetic activity. Then, about 11 years from now, the solar cycle will conclude: Sunspots will fade away and the sun will again grow quiet.
A violent, active sun, as seen in ultraviolet light in October 2014—near solar maximum in its 11-year solar cycle. As the sun approaches solar minimum, scientists are trying to predict the timing and strength of the next solar maximum.