In April we reported on the deep and ongoing lull in solar activity, noting that the predicted sunspot minimum, which comes about every 11 years or so, seemed to be longer and quieter than usual. (A sunspot is a dark patch on the sun that marks a region of elevated magnetic activity.)

At that time, 2009 was on pace to surpass 2008 in terms of sunspot-free days, as observed from Earth—and 2008 was already the second-quietest year of the past century. The solar cycle is no mere astronomical oddity: so-called space weather that originates from solar activity can have very tangible effects on Earth and its environs, disrupting power grids, upsetting satellite communications and causing pipelines to rust.

Although the solar doldrums described last month have continued apace, there are signs that the sun is stirring from its slumber. One of NASA's twin STEREO spacecraft has spotted solar activity brewing beyond the solar horizon—the two spacecraft are positioned in complementary orbits, one leading Earth around the sun and one trailing, allowing views of different areas of the sun than are visible from Earth.

The "behind" member of the STEREO team—that is, the spacecraft trailing Earth—spotted a large flare and a violent plasma eruption called a coronal mass ejection on Tuesday [see video below]. The blast was "probably the brightest one we've seen in, I don't know, the last year at least," says Michael Kaiser, the project scientist for STEREO at NASA's Goddard Space Flight Center in Greenbelt, Md. "It's been dead quiet."

Two days later the region remains astir, marked by what appears to be a pair of sunspots [see upper left in photo above], still out of view from Earth. The active area should rotate into view for Earth-based observers tomorrow, Kaiser says. "In 2001, when we were at solar max, we wouldn't have looked at this twice," he says. "But these days, we'll take anything we can get."

Forecasters of space weather can use the STEREO spacecraft to preview the solar activity that our planet will face in the coming days. At the moment, Kaiser says, the trailing STEREO orbiter sees areas of the sun that will be visible from Earth in about three days, but in two years' time the twin spacecraft will be separated by 180 degrees, allowing simultaneous observation of the entire sun for the first time. Given the duration and extremity of this solar minimum, forecasters at the NOAA Space Weather Prediction Center are revising their 2007 predictions for the next solar cycle; their forecast of the start, peak, and intensity of the next cycle will be announced tomorrow.

Image and video courtesy of NASA