The image above shows predicted rise and fall of sunspot activity during a Solar Cycle. Image source: NASA.
Born on January 24, 1882: Harold Delos Babcock, an astronomer who studied sunspot cycles and the sun's magnetic polarity during each approximately 11-year cycle.
That the orientation of the sun's poles changes, routinely, may come as a surprise, but, right now the sun's poles are upside down. The sun looks the same, but every 11 years or so, things flip over again as the Solar Cycle progresses, reaches, and passes its midway point. (The Earth's polarity also changes, but with much less regularity—the last change was more than 750,000 years ago!).
According to NASA, "graphs of sunspot numbers resemble a roller coaster, going up and down with an approximately 11-year period." It is at the high point, the "Solar Maximum," that astronomers have discovered that the magnetic orientation of the sun changes. In February 2001, NASA reported on the "flip" as the Solar Cycle 23 hit Solar Maximum: "The Sun's magnetic north pole, which was in the northern hemisphere just a few months ago, now points south."
While the magnetic flip has come to represent an expected part of each solar cycle and an indication of Solar Maximum during the approximately 11-year cycle, forecasting the "peak" of a solar cycle remains variable. Scientists are sure the reversal will happen, but pinpointing "when" is often only possible as we near the Solar Maximum. A survey of reports over the last several years regarding Solar Cycle 24, our current cycle, shows that NASA made several predictions that indicated a "peak" in 2011 or 2012. Indeed, in an account of the 2001 flip, NASA noted, "The Sun's magnetic poles will remain as they are now, with the north magnetic pole pointing through the Sun's southern hemisphere, until the year 2012 when they will reverse again. This transition happens, as far as we know, at the peak of every 11-year sunspot cycle—like clockwork."
They were close. Revised NASA forecasts now posit a "peak" for Solar Cycle 24 in mid-2013, with an unusually low number of sunspots during the Solar Maximum, the lowest since 1928.
It's not a clock you'll want to base your day-to-day activities upon, but the "clockwork" behavior of the Solar Cycle is interesting to watch and leads to much discussion and prediction from armchair astronomers and observatory-researchers alike. Students, too, can jump in and learn more about sunspots, magnetic fields, and the Solar Cycle. The following Project Ideas give students a chance to use publicly-available, historical data to learn more:
Update! Solar Max Means Amazing Skies
A related effect of the approaching solar maximum is an increase in activity that translates into amazing aural displays. Check these beautiful photos of the northern lights in January. See also, the "Spectacular Northern Lights From Solar Storm Wow Skywatchers" report.