Solar Cycle 24 is officially here, say the professional sunwatchers at NOAA's Space Weather Prediction Center.The start of a new 11-year-long activity cycle was confirmed by January 3rd appearance of a sunspot — not just any sunspot, but one at a high solar latitude and with magnetic polarity opposite that of its predecessors.
Scientists knew something like this was in the offing. A magnetic cluster seen in mid-December had the looked-for polarity and position in the Sun's northern hemisphere. It just hadn't coalesced into a distinct spot.
Sunspots, caused by magnetic knots, look dark because they are a few thousand degrees cooler than the surrounding surface. When more sunspots pop up, so do solar flares and the more powerful coronal mass ejections (CMEs), the most violent explosions in our solar system. Both flares and CMEs can hurtle "storms" of superheated particles, X-rays and ultraviolet radiation toward Earth. Our planet's magnetic field generally does a good job of deflecting these storms, but satellites and astronauts can be vulnerable to harmful — even lethal — doses of radiation. Flares and CMEs can sizzle out power grids, interfere with communication and GPS satellites, and create dazzling auroras.
In recent months the sunspot count has varied between zero and a few dozen, according to weekly reports sent to Sky & Telescope by a network of about 30 observers coordinated by Texas amateur Tom Fleming. But the numbers are certain to rise in the weeks and months ahead.
Space-weather scientists are split on the strength and timing for Cycle 24's upcoming maximum. Some models predict a strong cycle (140 sunspots peaking in October 2011), while others portend a weak one (90 sunspots in August 2012). The "strong" proponents look at factors from preceding cycles, while the "weak" teams focus more on the poles' magnetic fields during the tapering of the previous cycle.
Predicting sunspot cycles is an emerging field. This is only the third time scientists have attempted to forecast the Sun's activity, but they're gaining experience and confidence. The sooner more sunspots with traits like this one start springing up, the more likely the new cycle will be a strong one, with more frequent solar outbursts. If sunspots don't appear in droves by the middle of next year, it may be a weaker cycle.