Steamboat Springs Excitement built this past week when the strongest solar flare in nearly five years erupted on the sun, precipitating a chance for a large geomagnetic storm. As it turns out, the blast was rather weak when it blew past Earth on Thursday night, but the message was clear — solar activity is heating up again after a prolonged lull.
Astronomers who study the sun are the first to admit that there is much they do not yet understand about the details of solar activity. Forecasting the sun’s episodes of fitful behavior is an inexact science at best.
Here’s what we do know: The number of sunspots on the face of the sun is an indicator of the level of solar activity, and the number of sunspots waxes and wanes in an 11-year cycle. That is, every 11 years the sun becomes very active, then grows quiet for a few years. This solar cycle is related to the sun’s differential rotation — the equator spins faster than the poles — and how it causes the sun’s magnetic field lines to twist up and snap like rubber bands.
We have been in an extended lull in solar activity for the past three years and only recently have the sunspots returned. Solar forecasters have had to extend and downgrade their predictions for the next solar maximum because of this prolonged quiet period. As recently as 2008, solar astronomers predicted that the next peak in activity would occur in 2012 and be 50 percent higher than the last one in 2000-01. More recent predictions now call for a very weak solar maximum around July 2013, so weak that they now are expecting fewer than half of the sunspot numbers that we saw during the last solar maximum. What eventually will come to pass is anyone’s guess.
On Feb. 12, a small sunspot group appeared on the sun. During the next two days, it rapidly grew into a behemoth larger than the planet Jupiter and crackling with powerful solar flares. Late on Valentine’s Day, an X-2 class solar flare launched a billion-ton cloud of high-energy charged particles directly at the Earth. Such a cloud, as it blows by us, can stretch and distort the Earth’s own magnetic field and generate electrical currents in Earth’s atmosphere, creating colorful displays of dancing lights in the night sky called the aurora borealis, or northern lights. Usually confined to the regions near the North Pole, auroras occasionally can appear over mid-northern latitudes like Colorado. Between 1998 and 2005, I saw at least a dozen dazzling displays of the northern lights over Colorado. Then, the sun shifted into low gear and there haven’t been any since.
But if last week’s big sunspots and flares are harbingers of things to come, then we can look forward to some auroras over Colorado in the near future. For up-to-the-minute information on sunspots, solar storms, and auroras, visit the NASA website, www.spaceweather.com.
Professor Jimmy Westlake teaches astronomy and physics at Colorado Mountain College’s Alpine Campus. He is an avid astronomer whose photographs and articles have been published all across the world. Visit his website at www.jwestlake.com.