The Last Hoorah for Solar Cycle 23?

Magnetic activity on March 27th; white indicates N
magnetic poles, black S. Credit: ESA/SOHO/NASA.

A few blogs back I wrote about the 11-year cycle of ups and downs in solar activity--the Solar Cycle --and how over the last year or so the baton was supposedly passed from Cycle 23 to Cycle 24. But there has been an occurrence on the Sun that suggests we may be in somewhat of a gray zone….

For the past two or three years, the Sun has been downright boring. We set up our Sunspotter telescopes for visitors and try very hard to make what we see seem interesting--"See that perfectly blank circle of light? That’s the Sun! Really it is!"

About a week ago, the tedium was suddenly broken by a train of sunspots that rotated into view on Sun’s disk. Five--count'em-- five sunspots! Finally, something to actually look at! And in the eyepiece of our Coronado Hydrogen-Alpha filter telescope there were filaments and plage! What are filaments and plage? Exactly! People wanted to know….

Then came the weird part: these were not Cycle 24 sunspots (I am not the Dread Pirate Roberts…); they were refugees from the supposedly defunct Cycle 23. While the distinction may be a fine point that doesn’t worry most of our visitors, it can still be a good talking point.

So, why were these five sunspots fingered as old solar trekkers rather than members of the next generation? It all comes back to what a solar cycle is--and sunspots, flares, prominences, and plage are merely details: manifestations of the Sun's magnetic convulsions. The Sun, like the Earth, generates an enveloping magnetic field--a big donut with a north and a south magnetic pole. On smaller scales there are plenty of twists and swirls and knots in the field caused by local "hot spots" of magnetic activity--which are what produce features like sunspots in the first place.

At solar maximum--the peak of activity of a solar cycle--the Sun's magnetic poles flip over, or reverse. In fact, it's this reversal that really lets us know when a solar maximum has arrived. (Earth's magnetic field also reverses polarity periodically--although this only happens every 200,000 years, on average.)

At the beginning of a solar cycle, new sunspot activity can be found at high solar latitudes, and as the cycle progresses, activity migrates toward the equator. On a finer nuance, the magnetic polarity of sunspots--which can be N or S, and are usually paired up, like the two ends of a bar magnet --are typically oriented east-to-west on the Sun's surface, one leading to the other as the Sun rotates. Which type of pole (N or S) leads and which trails depends on the overall magnetic "flip" state of the Sun's magnetic field.

To round out this report, the five surprise sunspots of yesterweek were lined up close to the Sun's equator, and the orientation of their magnetic poles bespoke their affiliation with the outgoing magnetic administration (Cycle 23). So far, only a single, high-latitude, reverse-polarity sunspot observed last January has signaled Cycle 24 .

Who knows? Maybe the magnetic candidates of Cycle 24 are still holding primaries, caucuses, and debates and have yet to begin some serious campaigning…

Benjamin Burress is a staff astronomer at The Chabot Space & Science Center in Oakland, CA.

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