The sun is throwing a fit. For the second time this week it has launched massive chunks of itself at us—from 93 million miles away.

Don't be offended: This is all part of the normal solar weather cycle. Every so often, turbulence on the sun's surface erupts, shooting radiation and ionized particles earth-ward. When it's bad, it can fry satellites, and take them offline, disrupt the electrical power grid and expose astronauts and airline passengers to harmful radiation.

The solar storm that reached us yesterday turned out smaller than expected, causing no-known damage. But, if you were lucky, it did treat you to celestial nighttime light show.

Solar storms are what create the aurora borealis—the ethereal colored lights sometimes seen dancing in the night sky, especially at high latitudes.

But catching auroras from solar storms remains largely a matter of luck. Despite almost 200 years of working on solar storm predictions, scientists still have but a few hour's warning that a storm's a brewin'. And they have just a few minute's warning about how intense it will be. So often people who spy the auroras have no idea they're coming until they've arrived.

More seriously, airline operators and electrical grid managers would love more warning about when solar storms will hit and how bad they will be. If it's looking bad, they can then ground or reroute planes and power down the grid transformers. But these things take time, and more advance warning will help them operate safely and more efficiently.

While terrestrial meteorologists have gotten pretty good at knowing where storms will hit and how intense they will be, space weather is still in its infancy. "The general principles overlap quite a bit, but the physics is really different," says Robert Rutledge, lead of NOAA's forecast office at the space weather prediction center. Atmospheric forecasters, for example, get to ignore magnetic fields. For space weather forecasters, that's where much of the fun is.

The first indication that something is awry on the solar front comes in the form of an observed explosion on the sun's surface (as seen with the Solar Dynamics Observatory). Flares are relatively small, fleeting eruptions of magnetic energy that send forth high-energy protons and X-rays. Coronal mass ejections are bigger, more disruptive, and more exciting. A massive gas cloud breaks free of the sun's outer plasma layer, enters the solar wind and races outward, sometimes whooshing straight toward Earth.

"We live with very little information between sun and Earth. So this cloud makes it 92 of the 93 million miles," says Rutledge. "Then and we measure what's in it with the ACE spacecraft."

The ACE is the Advanced Composition Explorer satellite, which rests about a million miles away at a stable (Lagrangian) point between Earth and the sun. It measures the intensity of the incoming charged particles, giving Earth-bound forecasters a heads up of about 15 minutes. That's not a lot of time to take action if the storm's intensity is worse than expected, says Rutledge. Infrastructure managers can thus be caught off guard.

courtesy of Neel Savani/Solar Dynamics Observatory

Upon arriving, the charged particles set up a huge current in the ionosphere (moving a magnet across a coil of wire will induce a current in the same way). If you've seen the aurora borealis in the last few days (lucky you), you're spying ionized plasma washing over the atmosphere, pouring energy into it. "And it lights the sky up like a neon sign, essentially," says Rutledge.

Those who run airlines and electrical grids, among others, would love to have more advanced warning of a storm, and a better idea of its intensity to help them plan for events. While the observational equipment for gathering space weather data essentially has not changed for 20 years, recent advances in solar storm forecasting have come from better weather models and improvements in our basic understanding of solar physics.

For example, a group of researchers recently proposed a new technique for guessing the orientation of magnetic field in coronal mass ejections. CMS are basically big magnetic bubbles in space that act like a dipole magnet. Earth acts like another. If similar ends of the magnets are facing each other they'll repel, and the storm will be much weaker. If they attract, it will be far more severe.

"At the moment, when the cloud leaves the sun we have no idea what it is going to do," Rutledge says. Knowing more, he says, would help him give a day's warning, rather than minutes, making his job easier and making it more likely that you'll know just when to spot the northern lights.