On a crisp, clear night last July, Dr. Michael Klein, a physician and amateur astronomer from New York City, stood alone in the crows nest of a cruise ship sailing from Seward, Alaska to Vancouver, British Columbia. After 11 p.m. local time, the summer sun had finally set beyond the horizon. As Klein looked north, the sky suddenly erupted in a veil of green light. "It started out as a hazy cloud," Klein recalls. "Then it formed a green arc that gradually grew in size." Within minutes, rays of light fanned out like a giant curtain spanning from the horizon straight overhead. "It looked like it was moving, like a flag waving across the sky," Klein says.

"Were approaching a solar maximum," Vondrak explains, a peak in the suns 11-year activity cycle. A "solar max" is measured by observing an increase in sunspots. These dark splotches on the suns surface that indicate storm activity. The stormy disruptions in space associated with a solar max (and the few years that follow it) cause the auroras to extend toward the equator from their usual perch above Earths magnetic poles. That increases the odds of seeing an aurora in your own backyard, says Vondrak, provided that city lights dont obscure your view.

Scientists have known about the link between the sun and auroras since 1859, when Richard Carrington, an English astronomer, observed a solar flare, a burst of storm activity on the suns surface. Two nights later, massive auroras shed their light over Europe. Carrington noted the connection.

Over the past few decades, scientists have painted a more complete picture of aurora formation. The drama begins on the fiery, tumultuous surface of the sun, which continuously ejects plasma, a hot, gaseous mixture of electrons, protons and ions. Streams of plasma, the so-called solar wind, blast through space at speeds of about 250 miles (400 kilometers) per second. During a solar max, storms on the suns surface become even more intense, spewing powerful solar winds with speeds of nearly 1,240 miles (2,000 kilometers) per second.

Gusting past Mercury and Venus, these solar winds take about two or three days to reach Earth. Fortunately, the hot plasma doesnt come slamming into the planet with a cataclysmic blow. About 40,500 miles (65,000 kilometers) above the surface, the solar winds collide with Earths magnetic field. The field deflects the winds like a giant shield. But instead of stopping short, the plasma continues to blow past Earth, distorting the magnetic field on the "night" side of the planet into a comet-shaped region known as the magnetosphere.

As the plasma circulates within the magnetosphere, it generates one key ingredient for aurora formation: high-energy electrons. Because of the configuration of Earths magnetic field lines, Vondrak says some of these high-energy electrons are funneled into two large oval regions near Earths magnetic poles (one in each hemisphere). These so-called auroral ovals are the "studios" for aurora formation.

Auroras form over the polar openings in Earth's magnetic field.

Times are better than ever for catching an aurora. With satellites monitoring solar activity around the clock, scientists are getting better at predicting auroras. These predictions are posted on the internet, giving this generation of aurora enthusiasts an even better chance of seeing a good show.

Unfortunately, the predictions arent always accurate. Vondrak likens aurora forecasting to predicting tornadoes. "You can know which weather conditions promote tornadoes, but actually predicting when a tornado will touch down is very difficult," he says. Likewise, scientists can detect storm activity on the sun, but knowing whether, when and how they may interact with Earths magnetic field is another story.

For the determined, the best advice for seeing auroras over the northern hemisphere is to head north. "Every bit you head north, the more often you see auroras," says Patrick Newel, a research physicist at Johns Hopkins University. For example, during a solar max, the chance of seeing an aurora over Georgia is about 1 percent, but catching one over Canada is almost a sure thing. The best time for viewing is from dusk until just past midnight. You may want to plan your sky search for spring and autumn, when the most vigorous auroras tend to appear. They last from a few minutes to a few days. And remember, youll need a dark, cloudless night with no moon, so maybe treat yourself to a long weekend away from the city.

If youd like a guaranteed front-row seat (including popcorn) stay tuned. In late spring or early summer, Imax theaters will present Solarmax, which will feature scenes of auroras glimmering over Alaska and Greenland. "Sounds nice," says Klein. "But theres nothing like the real thing."