YOUR MOTHER told you never to look at the sun, because if you did it would ruin your eyes. But even if you gazed directly into our star’s glare, odds are that all you’d see is the yellow surface of a big ball of burning hydrogen gas, 865,000 miles across. It’s what you can’t see that’s important: the 30,000-mile dark patches known as sunspots, and solar storms that shoot gusts of charged particles toward Earth at a million miles per hour. Such solar spectacles create a combination of events that can knock out pagers and cell phones, and trigger power outages for millions of us here on Earth. Since 1996, solar weather has caused nearly $2 billion worth of damage to satellites. Scientists have been studying sunspots for millennia—extremely large spots are sometimes visible to the naked eye, and were recorded by Chinese astronomers as far back as the year 301. The invention of the telescope in the early 1600s allowed astronomers to observe the sun in more detail. In recent decades, investigators have turned to satellite technology to create three-dimensional pictures of the star. Since 1995, physicists at Stanford University, Lockheed Martin, and NASA have been using one satellite, the Solar and Heliospheric Observatory (SOHO), to illuminate the sun's inner workings. And they are preparing to launch a new satellite in 2007 that will give them even better insights. Currently, some of SOHO's instruments analyze the spectrum of light emanating from the sun—from infrared to X-ray frequencies—to investigate its atmosphere. But another instrument, designed by Stanford physicist Phil Scherrer, allows him and his colleagues to fathom the depths of the fiery ball by “listening” to sound waves generated from within. “Every time we look at the sun with a new instrument, we find something surprising,” says Karel Schrijver, an astrophysicist at Lockheed Martin’s Solar and Astrophysics Laboratory in Palo Alto, California. For instance, this year researchers unlocked the secret to how irregular bright patches on the sun, called supergranules, appear to move across its face. Ultimately their mission is to understand and predict the behavior of magnetic fields roiling below the sun’s surface that trigger the solar storms and wreak havoc for us at home. The researchers also want to understand the intricacies of solar weather patterns over decades and centuries. Increases in sunspot activity have been linked to warm spells on earth, whereas quiet periods may correlate with ice ages. Insight into solar cycles may therefore provide clues to planetary climate change. Just as the Earth has layers—an iron core and molten mantle, topped by a rocky crust—so does the sun. The star has an inner core, a 15-million-degree sphere of gas. There, a nuclear reaction converts hydrogen atoms into helium, producing the energy that makes life on Earth possible. But Scherrer and his collaborators are more interested in the sun's outermost layer, also composed of hydrogen and helium gas but at temperatures ranging from about 2 million degrees near the core to 6,000 degrees at the surface. Gas atoms at such searing temperatures become separated from their electrons, creating a collection of charged particles known as plasma. As a result of the temperature gradient, the outer layer “boils” like a pot of water: Bubbles of plasma called granules—which are about the size of Texas or California—rise up from the bottom. At the surface, the plasma cools and spreads to the sides, then it drops down again to the bottom of the layer. Such a cycle of movement driven by warming and cooling is called convection, which is why the outer solar layer is known as the convective zone. Granules and convection are the key to how the Stanford physicists “listen” to the sun. Think of placing your hand on the surface of the water in a swimming pool, and pulling down suddenly. The water comes in over the top of your hand, and then waves go out from the sides. The same thing happens when the cooled plasma drops back down from the sun’s surface, except the downdraft in this case creates sound waves. The waves travel through the sun and are affected by whatever they encounter along the way. Millions of granules on the sun’s surface produce millions of sound waves. “It’s like a bell in a sandstorm,” Scherrer says. The waves start bouncing around inside the sphere, and some of them wind up back where they started and create repeating patterns, or resonance. These patterns are similar to what you hear when you pluck a guitar string—the sound reverberates for a while before it dies off. As sound waves continue to form from new granules, they overlap to reinforce and stabilize each other, so the sound doesn’t die off. And the resonating waves cause the sun’s gaseous surface to actually pulse. As a result, the sun becomes a huge pulsating ball. The SOHO satellite, launched in 1995, carries instruments designed to measure those pulses. “People can make models all they want, but there’s nothing like having data,” Scherrer says. The satellite moves in a “halo” orbit balanced 1 million miles from the Earth and 92 million miles from the sun. Scherrer and colleagues rely upon an instrument aboard SOHO called the Michelson Doppler Imager (MDI), which monitors slight changes in wavelengths of light rays emitted from the sun as it pulses toward and away from Earth. From those pulses, the scientists then use computers to calculate information about the sun’s overall sound resonance and the original sound waves making up that repeating pattern. In the process they get details about the sun’s interior—information that typical light-viewing telescopes can’t reveal. For example, they can pinpoint areas of higher temperatures or stronger magnetic fields, which are produced by the flow of charged particles in solar plasma, because sound waves travel faster through such regions. And because sound waves also come from the back of the sun, they can get a picture of activity there as well. The satellite data have shed light on several of the sun’s secrets. One mystery centered around bright, 20,000-mile-wide swaths of plasma—known as supergranules—that were thought to move horizontally across the solar surface faster than the sun rotates. Scherrer and colleagues, analyzing data obtained from MDI, found that scientists had it all wrong: The data demonstrated that supergranules don’t actually move; rather, the plasma is just rising up and down, like sports fans doing the wave in a stadium. The next challenge is to figure out what’s generating the supergranules in the first place. Scherrer thinks the cause is some sort of interaction between smaller granules and the sun’s rotation. Imager data has also revealed another surprise for solar physicists: Sound waves travel through the sun at speeds different than expected—moving more slowly in the core, but accelerating significantly at the boundary where the inner and outer layers meet. Because the speed of sound depends on the compactness of the material it passes through, this means that the scientists' original estimates of the sun’s internal density are incorrect. “There’s something in the core that our model has wrong—some sort of mixing that our model doesn’t have” says Scherrer, who plans to investigate further. IN THE MEANTIME, Scherrer has also been busy studying sunspots, which can produce effects felt 92 million miles away on Earth. A sunspot forms when a cluster of magnetic field builds up at the bottom of the convective layer. Then, because plasma is less dense in a strong field, the cluster becomes buoyant and rises to the surface, forming a dark blotch on the face of the sun. Sunspots can last for days or weeks, and occur in pairs: Like two ends of a bar magnet, one will have positive polarity and the other will be negative. Sunspots cause trouble on earth when two sets of them interact. Underneath one sunspot pair, another will eventually form and rise to meet the spots already at the surface. The charged particles in the plasma within sunspots produce strong electric currents. So when two spots meet, it’s like two crossed wires short-circuiting to blow a fuse or start a fire—but on a massive, violent scale. The two spots actually annihilate each other, releasing large amounts of energy, charged particles, and magnetic field into the sun’s atmosphere and beyond—a solar flare. A very large flare is called a coronal mass ejection. A coronal mass ejection is like a very strong gust of the solar wind that regularly carries energy to Earth in the form of light and charged particles. “Ejections to the side are fine, it’s those in your face that are a problem,” says astrophysicist Juri Toomre from the University of Colorado, Boulder. The amount of energy released by a flare can equal up to a billion million tons of TNT. Earth’s magnetic field guides charged particles into the atmosphere, where they encounter gas particles and start to glow. This is the source of the aurora borealis, or Northern Lights. A supersize coronal mass ejection may wreak havoc on cities, because power grids can act like antennas for the electrical currents generated by the charged solar particles. A solar storm in 1989 knocked out Quebec’s power system and plunged six million people into darkness. The damage took months to fix. The Space Environment Center (SEC), operated in Boulder, Colorado, by the National Oceanic and Atmospheric Administration, tries to forecast such events, providing information to telecommunications companies, the military, and NASA. Not only are power grids in danger of damage from ejected particles, but so are telecommunications satellites cruising above the earth’s protective atmosphere, says Joseph Kunches, chief of space weather operations at SEC. A 1998 storm caused a blackout of service for nearly 40 million pagers. The government’s program to locate cell phones through global positioning satellites would also be vulnerable to solar storms, Kunches says. And airplanes and the Space Shuttle are susceptible to solar storm radiation. The instruments on solar research satellites “have made us forecasters a lot smarter,” Kunches says. He would like to see a better warning system, so that power grids and satellites could be operated in “safe”—albeit less profitable—modes and airplanes rerouted as necessary. When a big solar storm struck in July 2000, he notes, it caused only minor damage partly because scientists had issued an advisory that a major sunspot region could turn deadly. Scherrer and Schrijver believe that better forecasting will come through deeper understanding of the magnetic fields and flows that produce sunspots. Such knowledge could lead to predictions of when a second spot will rise to produce a flare or ejection, and of just how big an ejection might be. Currently, however, the orbit of the SOHO satellite only allows Scherrer and colleagues to get nonstop data from MDI for two months of the year. MDI’s view of the sun is also not very detailed, offering high magnification of an area that’s only about a fifth of the visible surface, allowing them to observe a spot only for a day or so. “It gives us snapshots,” says Scherrer. He’d much rather have a movie. That movie is where a new satellite and new instrumentation come in. Four years from now, Lockheed and NASA are planning to launch the Solar Dynamics Observatory (SDO), which will carry MDI’s successor, the Helioseismic Magnetic Imager (HMI). HMI will download solar data 24/7 for all but a couple of days of the year. It will also have high magnification of the entire sun, roughly the equivalent of going from a 14-inch to a 56-inch television. The new technology will allow the researchers to follow sunspots throughout their typical 10-day journey across the solar face. Scherrer also wants to track sunspots over longer periods. For reasons that aren’t understood, the number of sunspots regularly waxes and wanes over an 11-year cycle. During periods of maximal activity, sunspots are found closer to the sun’s equator, whereas they migrate to the poles as the cycle winds down into a minimal period. Scherrer wants to know what’s in the convective layer that leads to this behavior. Another question scientists want to explore is the connection between sunspots and climate. From the 1100s to the 1500s, astronomers observed a period of extremely intense sunspot activity, corresponding to a global warm spell. If you’ve ever wondered how Greenland got its name, this is why: At the time it was discovered, it had grass. This greening of the Arctic was followed, however, by the “little ice age” in Europe, a period marked by only a handful of sunspots instead of hundreds. These climate cycles appear to correlate with a 0.1 percent change in solar luminosity between periods of intense and lackadaisical sunspot activity. Understanding—and predicting—these patterns may provide insight into global climate change. In the long run, Scherrer’s goal is to put all of the pieces of the puzzle together—the mysteries of magnetic fields in the convective layer, how sunspots form and interact, whether a solar flare is imminent, and the secrets fueling the solar cycles. “We want to understand the effects on a technological society due to a variable sun,” Scherrer says. “If we can understand how the material underneath drives the process, then maybe we can predict the process better.” Now and then, even those of us without access to NASA satellites can witness one of the solar events that inspire his work. Despite your mother's admonitions, it actually is safe to look at the sun when it touches the horizon at sunset. Perhaps one day, you'll manage to see a giant sunspot—as Scherrer himself did a few years ago—and get a first-hand glimpse of the activity that forms the heartbeat of our solar system.