The sun may seem a placid presence, but next week it will enter the peak of its mysterious 11-year cycle, a period of furious activity and violent space storms.
The solar maximum, as it is called, is an interval of months marked by wrenching solar activity that hurls billion-ton blasts of radioactive particles, X-rays and magnetic energy toward Earth. Such blasts can disable satellites, knock out navigational systems and darken entire cities by frying electrical grids.
As if on schedule, one of these space storms was expected to hit Earth this weekend--the effect of two solar flares that erupted from the sun Thursday. A storm in 1989 knocked out power in Quebec for more than nine hours and sent garage doors in San Francisco flapping open and closed. A storm in 1859 lit skies over Cuba with colorful displays of northern lights and quieted the communications technology of the day: the telegraph.
The current maximum is hitting an Earth that is increasingly vulnerable, one whose inhabitants are more reliant on space satellites, interconnected power grids and sky pagers. Five years ago, there were 250 satellites in orbit. Today, there are about 800.
"Technology is getting so advanced, so pervasive and so sensitive that the small perturbations space storms cause are becoming dangerous," said George Siscoe, a Boston University astronomer.
In the past, solar punches have hit our hapless planet with almost no warning. This time, although Earth is far more susceptible to major damage, it is also better prepared for the coming threat.
The planet's first defense against solar weather lies deep in an office building in Boulder, Colo.--the National Oceanic and Atmospheric Administration's Space Environment Center. There, solar forecasters issue warnings based on the sentry they stand around the clock, watching on monitors should the grouchy sun twitch or belch.
Alerts mean satellites and power plants might be powered down for protection. Any planned spacewalks are canceled to protect astronauts from radiation poisoning, and work requiring use of satellite positioning devices is often postponed.
Through history, the activity of the sun has proved mischievous, unstoppable and most of all, unpredictable. Solar maximums are usually filled with solar flares, intense releases of energy from the 25-million-degree sun, and coronal mass ejections--violent events that hurl portions of the sun's surface into space.
But this solar maximum has been perplexing to sun watchers. Aside from the current storm, the sun has been, on average, far less disruptive than expected during the buildup to peak activity.
"That was kind of a surprise to me," said Jo Ann Joselyn, an astrogeophysicst at the University of Colorado. "But I'm not turning my back yet."
The unexplained lull underscores just how little is known about the 11-year sunspot cycle.
Sunspots are dark, cooler blips on the surface of the sun, driven by its powerful magnetic field. Growing as large as several billion square miles, they were first identified in 325 BC and have held a notorious (and often ridiculed) role in weather forecasting.
The study of sunspots began in earnest, and in secret, during World War II, when officers at battlefronts experienced crippling radio communication breakdowns during solar flares. Since then, it has become clear that sunspot activity is linked to solar storms and disruptions on Earth--though the ability to predict those events remains primitive.
A solar maximum, once fireworks start, provides an opportunity to better understand the sun and to hone forecasting skills.
The Space Weather Center relies on 1,400 sources of information about the sun, said its director, Ernest Hildner. Those constant data streams come both from satellites and from solar observatories, including one at Big Bear Lake. Set in the middle of the lake to shield it from image-distorting heat waves, the observatory captures some of the world's crispest solar photos.
Because of new links with solar cameras in Austria and China, that view will soon be available around the clock, said Bill Marquette, Big Bear's chief observer. For Marquette, sunset--and the long, dark night that follows--can be a time of extreme frustration.
"If there's an active region on the sun, I wake up in the middle of the night and wonder, 'Is there a [solar] flare?' " he said.
A major contribution to forecasting comes from a 3-foot-tall satellite named ACE, or the Advanced Composition Explorer, which has been in orbit since 1997, capturing and analyzing the many solar particles streaming past.
"The primary goal is to determine what the sun is made up of," said Ed Stone, director of the Jet Propulsion Laboratory in Pasadena and a Caltech physicist who is the lead investigator for the satellite mission. "You might say, 'Gee, don't we know that?' But there's a lot left to learn."
Little ACE does double duty. Nearly a million miles from the Earth, it stands as the planet's only early warning system.