Like you and I the sun has cycles. None of us escapes the day-night rhythm of sleep and wakefulness. The most visible of the sun’s rhythms is the 11 year solar cycle also called the sunspot cycle. These vary from 9 to 14 years but the average is 11.
In a typical cycle, the number of sunspots and solar storms begins at a minimum, rises to a maximum and then returns to minimum. During solar maximum the sun is peppered with sunspots and powerful, aurora-producing flares are common; at minimum the sun’s face can be blank for days or even weeks. Minimums and maximums also vary. Some peaks are longer and more sunspot-rich than others, while “valleys” can be short or long with variable spot numbers.
The solar cycle was discovered by German astronomer Samuel Heinrich Schwabe in 1843 after he noticed sunspot numbers wax and wane in a regular pattern after 17 years of observation. Swiss astronomer Rudolf Wolf went back through previous sunspot records and reconstructed the sun’s ups and downs as far back as the mid-1700s.
Each cycle gets a number. Solar Cycle 1 spanned the years 1755 to 1766. The last, Cycle 23, peaked in April 2000 with an average of 120 sunspots per day around the time of maximum. This was followed by a deep quiet period or minimum between cycles 23 and the current 24th with a record number of 801 spotless days between October 2005 and May 2010. This past solar minimum, which bottomed out in December 2008, was the longest and quietest in over a century. Since then, but especially over the past year, activity has been steadily on the rise.
2012 has been a good year for sunspots, solar flares and auroras as we dig our way out of minimum and sail toward the next predicted peak in spring 2013. To date, the sun has kicked off about a half-dozen X-class flares. These are the most powerful variety with potential effects on Earth ranging from aurora creation to wreaking havoc with satellites and power grids. From late 2008 through early 2010 I recorded almost no auroras here in Duluth, Minn. In the past year however, we’ve been treated to several brilliant displays and at least 10 minor ones.
NASA solar scientists predict a very weak maximum in 2013 with an average of 60 sunspots daily. If this holds true, Cycle 24 would be the least active since Cycle 14 which peaked in February 1906 at 64. While this sounds like bad news for aurora watchers, don’t put on your long face just yet. Every cycle max, even the wimpier ones, feature powerful flares and crazy space weather.
“Even a below-average cycle is capable of producing severe space weather,” says Doug Biesecker of the NOAA Space Weather Prediction Center. “The great geomagnetic storm of 1859, for instance, occurred during a solar cycle of about the same size we’re predicting for 2013.”
That storm, called the Carrington Event, is named after astronomer Richard Carrington who spotted a brilliant flare through his telescope on September 1, 1859. Shortly before dawn the next day, the sky blew up in a brilliant display of northern lights visible as far south as Jamaica. Aurora-induced electric currents in telegraph lines shocked telegraph operators and set telegraph paper on fire.
“A report by the National Academy of Sciences found that if a similar storm occurred today, it could cause $1 to 2 trillion in damages to society’s high-tech infrastructure and require four to ten years for complete recovery,” according to a recent NASA press release.
We’ll soon see what Cycle 24 has in store. At the very least, more brilliant auroras are on the menu.