Death from the Skies!: These Are the Ways the World Will End... - Philip Plait (2008)

Chapter 2. Sunburn

IT’S JANUARY, THE DEAD OF WINTER ON THE NORTHERN hemisphere of Earth. During the short days, the Sun makes a desultory appearance low in the sky, only to sink below the horizon again a few short hours later. It can barely warm the planet, it seems. With the chill in the air, people don’t give the Sun a second thought. They wouldn’t even think it had much of an impact on their lives.

They’re about to be proven quite wrong.

The Sun is nursing a cosmic hangover. It has undergone some violent paroxysms over the past few years, erupting multiple times, sending tremendous blasts of matter and energy into space. Through sheer chance, these had mostly missed the Earth. The worst thing that had happened was one eruption nicking the Earth, causing beautiful aurorae at both poles, and disrupting some radio communications: an annoyance, but easily offset by the stunning display of northern and southern lights.

Things are on the decline now, and the Sun appears to be calming down. Scientists are just starting to think they can breathe easier.

They’re therefore caught by surprise when a vast group of sunspots peeks over the edge of the Sun. Sunspots are dark blotches of cooler material, caused by kinks and twists in the Sun’s magnetic field, and they are harbingers of solar activity. Scientists scramble to observe the sunspot group, bringing a fleet of ground-based and orbiting telescopes to bear on the star. They are greeted by an ugly sight: the Sun’s surface is gnarled, twisted, blackened, defaced by the spots. This group is a whopper, as big or bigger than the largest groups seen in 2003, which scientists still buzzed about.

For over a week astronomers nervously watch the active region, measuring its size, shape, and magnetic activity. The latter appears to have settled down, which could indicate either that the magnetic field is fading or that it is building up like a volcano.

They soon get their answer. The sunspots, normally dark, brighten tremendously in seconds, and stay bright for many minutes. At the same time, orbiting solar telescopes note wild magnetic fluctuations on the Sun, and minutes later are flooded with high-energy X- and gamma rays. Astronomers on the ground monitoring the orbiting observatories see unprecedented energy blasts, with measurements off the scale, when, suddenly, the data flow stops. Bewildered for a moment, they check their equipment, but then realize the problem is not on the ground, but in the sky: the huge influx of energy has fried their astronomical satellites.

Knowing that commercial satellites are at grave risk as well, the scientists make frantic calls to other observatories, but find the phones aren’t working either. Turning to their computers, they try e-mail, instant messaging, voice-over-Internet, anything, but communication is impossible. Nothing is working. Then their power goes out, and they realize things are about to get much worse.

Shortly after the flare, the Sun unleashes another blast, this time in the form of a brutal wave of subatomic particles. Traveling at phenomenal speed, the wave reaches the Earth, where it slams into and flows over the planet’s protective magnetic field. Submerged in the electromagnetic mayhem, satellite after satellite dies from an overdose of sunburn.

The effect reaches the ground as well. Transmission wires are suddenly overloaded with current, heating up, sagging, and snapping. Transformers are overwhelmed, exploding. Workers at electrical stations across the United States and Canada are snapped out of their routine and suddenly find themselves struggling valiantly and frantically to keep up with the cascading disaster, but it’s hopeless. Station after station goes down. Power goes out first to the U.S. Northeast, but within seconds the grid goes down in an expanding wave. Quebec, Boston, New York City, Philadelphia . . . minutes later, a hundred million people are without power at night in the dead of winter. They wake up the next morning to icy homes, without electricity, and with no means of finding out what happened.

Within hours, over half the planet is without power during one of the coldest winters in recent memory. Thousands die the first night, and many more follow over the next few weeks. The military jumps in, doing what it can to help those in need, but the sweep of the disaster is simply too broad. The number of deaths is staggering, an epic catastrophe on a scale unseen for a century. The economic impact alone is measured in the trillions of dollars, and entire nations go bankrupt.

Eventually, the Sun calms down. The active group of sunspots fades away. But magnetism on the Sun is fiercely complex. Within a few weeks, tangles and interconnections reappear in the solar magnetic field. Just as things on Earth start to settle, and people are able to bury the dead, another group of ugly sunspots begins to build on the star’s surface.


An occupational hazard of being an astronomer is getting free astronomy textbooks in the mail. Like e-mail spam (but tipping the scale at ten pounds), they come unannounced, and generally wind up in a used bookstore collecting dust (the real-world equivalent of the spam filter).

I can’t resist thumbing through them. I torture myself this way, knowing that I’ll find some odd chapter arrangement, some scientific error, some small turn of phrase that will irk me in some way. And always, without fail, I find it in the section about the Sun. Invariably, there will be some permutation of this sentence: “The Sun is an ordinary, average star.”

If you decide to read only this chapter and then close this book forever, then please walk away with just one thing: the Sun is a star, with all that this implies. The Sun is a mighty, vast, furiously seething cauldron of mass and energy. The fires in its core dwarf into microscopic insignificance all the nuclear weapons ever built by mankind. A million Earths would be needed to fill its volume, and the light it emits can be seen for trillions upon trillions of miles. Invisible forces writhe and wrestle for control on its surface, and when it loses its temper, the consequences can be dire and even lethal.

That is what it means to be an “ordinary” star.

Let’s be clear—there are lots of stars like the Sun, and if you phrase it carefully, then sure, the Sun is average. The smallest stars have roughly one-tenth its mass, and the largest have a hundred times its mass, so the Sun is somewhere near the low end of the range. But this neglects the actual population of stars: low-mass stars are far, far more common than their hefty brethren. More than 80 percent of the stars in our galaxy are lower-mass than the Sun. Roughly 10 percent have the same mass as the Sun, and 10 percent have more. So really, in a standardized cosmic test, the Sun scores pretty well. Maybe a B+.

Of course astronomers—and I count myself guilty here as well—do love to use diminutive adjectives when describing low-mass stars: dinky, tiny, feeble. But that’s hardly fair, either: even the smallest star is far, far larger than Jupiter, and Jupiter is pretty big; three hundred Earths would fit inside it, so even a small star is a huge object.

And yet the Sun is larger in size than the majority of stars in the galaxy: their median diameter is about a tenth that of the Sun. So even on a cosmic scale the Sun is big.

On a human scale, as you can imagine, it’s a scary, scary place.

The Sun is about 93 million miles away. If you could build a highway and drive there, it would take over 170 years. Even an airplane would take two decades to fly to the Sun if it could.

And yet . . . imagine it’s summer and you’re standing outside. You turn your face up to the Sun. Feel the warmth? Sure! The Sun is so bright you can’t even look at it. And if you stand there for more than a few minutes you risk damaging your skin.

The Sun’s fearsome power is generated deep in its core, where a controlled nuclear reaction is taking place: the Sun is continuously fusing nuclei of hydrogen together to create helium nuclei. Every time this reaction occurs a little bit of energy is given off, and in the Sun’s core the reaction happens a lot: every second of every day, the Sun converts 700 million tons of hydrogen into 695 million tons of helium.

The missing 5 million tons get converted into energy, via Einstein’s famous equation E = mc2, which shows that mass and energy can be converted back and forth into one another, and that a tiny bit of matter produces a whopping amount of energy. Five million tons is a huge amount of matter, the equivalent weight of seven fully loaded oil supertankers . . . and the Sun chews through that much hydrogen every second.6

The energy created every second in the core of the Sun—equal to the energy it emits from its surface—is the equivalent to the detonation of 100 billion one-megaton nuclear bombs. This is 200 million times the total explosive yield of every nuclear weapon ever detonated on, below, and above the surface of the Earth . . . and the Sun does this every second of every day, and will continue to do so for billions of years yet to come.

Some people like to say the Sun is essentially a giant nuclear bomb, but that’s misleading: a bomb explodes.7 But the Sun doesn’t explode, because it has a lot of mass. This means it has a lot of gravity, which balances the energy it generates. The heat produced makes the Sun want to expand (like a hot-air balloon expands), but the Sun’s own gravity holds it together. It’s a balancing act; in fact, a good definition of a star is a ball of gas with nuclear fusion in its center held together by its own gravity.

But just because the entire Sun doesn’t explode like a bomb doesn’t mean that explosions don’t happen. In fact, the Sun is capable of epic eruptions; but they’re not nuclear in nature, they’re magnetic.


When I was a kid (and sure, I’ll admit it: even today), I was fascinated by magnets. I had a few different kinds, and I would play with them constantly. I read a lot about magnetism, and in one of my books it said magnetism could be destroyed by heat. I (carefully!) held a bar magnet in a candle flame for a few minutes, and sure enough, after that it wouldn’t attract nails or needles anymore.

I was also something of an astronomy geek even then, and I had a book that talked about the magnetic field of the Sun. I remember being confused by this: how could the Sun have a magnetic field if it was so hot?

What I didn’t understand is that there is more than one way to create a magnetic field. Simply put, a magnetic field can be generated by moving electrical charges. When you turn on a light, for example, electrons (subatomic particles with a negative charge) flow through a wire from the wall to the light. This motion produces a local (temporary) magnetic field around the wire. When you turn off the light, though, the flow of electrons stops, and the magnetic field collapses.8

This has a very interesting—and useful—effect. If an electrically conductive object like a wire moves through a magnetic field, an electric current will flow along the wire. This current, in turn, generates its own magnetic field. If the current moves in just the right way, its magnetic field will reinforce the magnetic field already there and you get a self-sustaining system.

However, this only works if there is an outside source of energy to make things move. For example, you could use a crank to make a coil of copper wires rotate inside a magnetic field (generated by a permanent magnet). Your arm supplies the outside energy. Or, if you’re smart, and you want to make a lot of electricity, you stick this getup near a source of flowing water—say, inside a dam—and make giant turbines composed of copper that spin as water flows past them . . . which is precisely how hydroelectric power plants work. A system that converts mechanical energy to electromagnetism in this way is called a dynamo.

The Sun is just such a dynamo. Its interior is hot: so hot, in fact, that electrons are stripped off their atoms, allowing them to flow more or less freely. An atom that is missing one or more electrons is said to be ionized. As these electrons move in the ionized gas, they generate magnetic fields.

If the Sun were just sitting there in space, a nonmoving and non-rotating ball of hot gas, the electrons inside would move around higgledy-piggledy, and all those individual magnetic fields generated would be oriented in random directions and cancel each other out. But the motions of the electrons in the Sun are far from random. For one thing, the Sun spins on its axis once a month, and that can create streams of gas in its interior. This preferred direction of motion for the electrons means that their individual magnetic fields can build on one another like creeks all flowing into a river, creating a larger magnetic field.

If it were just that simple, scientists would understand everything about how the Sun works. But in reality the Sun is incredibly complicated, with a vast system of moving gas inside it. The heat from the core makes gas above it rise,9 generating towering conveyor belts of gas over 100,000 miles high, moving up and down inside the Sun. Other rivers of gas move around it like the jet stream does on Earth, and yet another set of streams flows north and south as well. When taken all together, the Sun more closely resembles a ball of writhing worms than a simple sphere of gas. It’s like a street map of Tokyo, but in three dimensions and changing with time as well. Because of this, the magnetic field of the Sun is a nightmare as well, making it ferociously difficult to understand. On the positive side, though, it also keeps a lot of solar physicists off the streets.

All of this together is what creates the Sun’s dynamo. The charged particles inside the Sun are moving in currents. These currents move inside a magnetic field, so the currents themselves generate a magnetic field, and the whole thing is self-reinforcing. The crank, in this case, is the Sun itself, with its own rotation providing the mechanical input energy needed to generate the dynamo. The Sun is huge and massive, so there is a vast amount of rotational energy to tap into. The solar magnetic field is created at the cost of the Sun’s spin, but it will take billions of years for the energy loss to result in a noticeably slower spin.

The Sun’s magnetic field is complicated and interesting, and by interesting, of course, I mean dangerous.

Or had you forgotten the title of this book?


Earlier, I mentioned that a star can be defined as an object with fusion in its center, whose tendency to expand due to energy production is balanced by its gravity.

Stars are a study in balance in this way. If gravity were weaker, they’d expand or explode. If their energy generation were a little weaker, they’d shrink or collapse (more about both of these in later chapters). Their rotation, chemical composition, gravity, heat, pressure, and yes, magnetic field all combine in exquisite balance to produce a stable star.

But sometimes things get out of whack.

When a simple magnetic field is illustrated, you usually see a set of lines emerging from the poles of the magnet, connecting one pole to the other. The field lines of a bar magnet, for example, look something like a doughnut. These magnetic field lines are useful to visualize the strength of a magnet: where the lines are bunched up together (like near the poles of a bar magnet), the magnetic field is stronger; where they are spaced out the field is weaker. If you place a small bar magnet inside the magnetic field of a larger magnet, the smaller one will align itself along the larger’s field lines. That’s why a compass points north; the needle is a magnet, and it aligns itself along the Earth’s magnetic field lines.

Things get complicated if the magnet is not a simple shape. If you bend a bar magnet, the field lines will bend as well. If you take a dozen magnets, a hundred, and throw them together, the field lines can get very distorted, because each bit of the magnetic field is attached to the object generating it. Mess with one and you affect the other.

The magnetic field of the Sun is generated by moving currents of gas—currents that get twisted, distorted, and bent around just like rivers on the Earth. These field lines may be generated beneath the surface of the Sun, but they don’t stay down there; they pierce through the surface, looping upward and back down into the interior in an incredibly complex, interwoven, and interconnected way. These magnetic field lines can really get their knickers in a twist, becoming entwined and entangled. When this happens, there are profound changes on the surface of the Sun.

For one thing, since the field lines and the gas are coupled, when the lines get tangled and compressed, the gas has a harder time moving around as well. It’s like a giant net is thrown over the gas, preventing it from moving freely. Hotter gas welling up from below can’t reach the surface, and regions where the lines are particularly dense begin to cool off. Since the brightness of the Sun is due to its temperature, a cooler region becomes dimmer, forming a dark area on the Sun called a sunspot. Because sunspots are inherently magnetic phenomena (they are really a cross section of the magnetic field lines where they intersect the surface of the Sun), they always come in pairs with reversed magnetic polarity: one is like a magnet’s north pole, and the other is the south pole.

Sunspots can be small, barely visible to telescopes on Earth, and they can be huge, dwarfing the Earth itself, with some so large that they can be seen by the naked eye when the Sun is on the horizon.10

In fact, it was the observation of sunspots that first keyed astronomers into the Sun’s magnetic field. Heinrich Schwabe was a solar observer in the early nineteenth century who counted the number of sunspots every day for decades. He discovered that the number of spots waxes and wanes with a period of about eleven years from peak to peak—we now call this the sunspot cycle. At the time of the maximum, there can be well over a hundred sunspots on the Sun, but at the minimum that number drops to essentially zero.

Schwabe decided to publish his results in 1859, and it was quickly determined that the times of peak sunspot number also corresponded to the times of peak magnetic activity on the Earth, indicating a connection between sunspots and magnetism. In 1908, the astronomer George Ellery Hale discovered that the magnetic fields in sunspots can be thousands of times stronger than the Earth’s, indicating the presence of intense energies being stored there.


This is a typical sunspot, appearing darker than the surrounding solar surface because of its cooler material. This particular spot is far larger than the Earth. The graininess of the Sun’s surface around the spot is caused by convection, rising currents of hot material that cool and sink back down into the Sun.


Which brings us back to balance. As the magnetic field lines tangle up, there is a balance struck between the pressure built up by the magnetic energy stored in them and the tension that exists in the lines. Imagine the magnetic field lines are like steel coil springs, all tangled together and interconnected. The springs are compressed and want to expand, but the tension of the intertwined mess keeps them from springing back. Now keep compressing them and adding more springs, again and again. The energy stored up would get pretty impressive.

What happens if you take a bolt cutter and snip one of the springs?

Right. Better stand back.

The same thing happens in a sunspot—in fact, much of the physics is pretty similar to a convoluted mess of coiled springs, with the analogous tension and pressure. As the field lines get more entangled, and more are added, the pressure builds up. Sometimes the pressure is relieved early in the process, and not much happens. But other times it builds, and builds . . .


Loops of extremely hot material flow up from the Sun’s surface, following along the magnetic field lines. When the loops get tangled or twisted, a flare or coronal mass ejection can be triggered.


Something’s gotta give.

Eventually, something does. The field lines emerge from the Sun in tall, graceful loops, with one footprint being the magnetic north pole and the other the south. If the gas flow zigs instead of zags, for example, the footprints can be brought together, or twisted past each other. The pressure in the coil goes up, but the tension can’t compensate. The line snaps.

There is a lot of energy stored in the field line (just like the energy stored in a spring). When it snaps—what solar physicists call magnetic reconnection—the energy is released. A huge amount of energy. The explosion is titanic, but in general constrained to a local region, causing what’s known as a solar flare.


By coincidence, a solar flare was first observed in 1859—the same year Heinrich Schwabe published his discovery of the sunspot cycle.

On September 1, 1859, astronomers Richard Carrington and Richard Hodgson were independently observing the Sun. Before their eyes, a small part of its normally calm disk suddenly exploded in intensity, becoming far brighter. This burst of emission lasted for five minutes, and even to this day may have been the most luminous flare ever observed. Within a few hours of the observations of the flare, magnetometers (instruments that measure the strength and direction of a magnetic field) on Earth went crazy, registering huge fluctuations in the Earth’s magnetic field.


The Solar and Heliospheric Observatory detected this massive flare from the Sun on November 4, 2003. It was one of three huge flares that surprised scientists that day; no such string of events had ever been witnessed before. They marked one of the most active weeks for the Sun ever recorded.


They didn’t know it then, but at that moment the study of space weather was born.

They also couldn’t have known that the flare was caused when tangled magnetic field lines on the surface of the Sun suddenly realigned themselves. The energy stored in them was released like a bomb—the equivalent of 15 billion one-megaton nuclear weapons, or 10 percent of the total energy output of the Sun every second concentrated into one spot—hurling high-energy photons (particles of light) and subatomic particles both upward into space and downward onto the surface of the Sun. A typical flare from the Sun ejects billions of tons of subatomic particles outward at speeds that reach five million miles per hour—and in 2005, one extraordinary flare launched a blast of protons that reached the Earth in just fifteen minutes, indicating they were traveling at one-third the speed of light. These subatomic particles blast outward, generally straight out from the center of the flare. Because of this, the particles launched upward and outward from the flare are generally not a problem to us on Earth: they are focused enough that they usually miss us, causing no grief.

But along with the particles shot into space, a huge pulse of particles is shot down, onto the surface of the Sun. This heats the gas there tremendously, and creates an incredibly strong pulse of light. Now, that may not sound like a big problem; after all, how bad can light be?

Bad. But it depends on the kind of light.

What we call “visible light” is a narrow slice of a much wider range of electromagnetic radiation. Infrared light, for example, has less energy than visible light, and radio waves have less energy still. Ultraviolet (UV) light has more energy than the light we can see. Still higher-energy light is X-rays, and on up to gamma rays. UV, X-, and gamma rays are dangerous in large quantities. Each photon carries so much energy that it can radically alter any atom it hits, stripping off the atom’s electron, ionizing it.

Flares give off a lot of this kind of light. And unlike the particles of matter emitted in a solar flare, this light spreads out. A flare on the edge of the Sun’s disk will almost certainly miss us with its particles, but any flare anywhereon the visible surface of the Sun is a potential danger because of the high-energy light it emits.

Picture a solar flare on the Sun: the tangled magnetic field lines over a sunspot suddenly snap, rearranging themselves, and releasing their energy. They heat the local gas up to millions of degrees, and a blast of X-rays surges outward.

Traveling at the speed of light, the high-energy radiation takes a little over eight minutes to travel the 90 million or so miles to the Earth. When it does, it slams into everything in its way: satellites, astronauts, and even the Earth’s atmosphere.

On the Earth’s surface, we’re protected from this onslaught by the thick air over our heads. But an astronaut in orbit is essentially naked, exposed to the wave of photons. A spacewalker caught by surprise will absorb many of the incoming X-rays, getting the equivalent of hundreds or even thousands of chest X-rays in a single flash.

X-rays are dangerous because when absorbed, they deposit all their energy into tissue. This can lead to cell and DNA damage. When DNA is damaged, mutations can occur that can (but do not always) lead to cancer.

Radiation absorption is measured in units called rems.11 Natural radiation coming up from the Earth’s surface surrounds us all the time; you get a dose of about 0.3 rem per year just by existing on the Earth. In high-altitude locations, like Denver, that can be as high as 0.5 rem due to both terrestrial and extraterrestrial sources. A dental X-ray, by comparison, gives a dose of about 0.04 rem, one-tenth of your normal annual background dose. The U.S. government has guidelines for employees who work in elevated radiation environments: the maximum safe whole-body dose is set at 5 rems per year.

A mild flare may expose an astronaut to several dozen rems of radiation. While that sounds bad, in fact the body can heal itself fairly well after such a one-time radiation dose. Cells heal, and small amounts of damaged DNA can be eradicated by the body’s natural defenses. That’s not to say it’s fun: the problems associated with this kind of dose are irritated skin and a higher risk of developing skin cancer or other forms of cancer. Male astronauts might also experience a temporary sterility lasting for a few months, and hair loss in both sexes is possible.

But if too much tissue is damaged, the body cannot heal itself. In a major flare, an astronaut could absorb hundreds of rems of X-rays. This can be fatal: there is simply too much cell damage for the body to repair itself. Over the course of several hours and days the astronaut suffers a slow death as cells die, the intestinal lining sloughs off, ruptured cells leak fluid into their tissue . . .the effects are horrifying. NASA takes this threat very seriously. When a flare is seen on the Sun, astronauts on the International Space Station retreat to a section that is more protected, letting the station itself absorb the radiation to safeguard the humans inside.

When astronauts return to the Moon they’ll have to deal with this as well. Lunar rock is an excellent absorber of radiation, so it’s likely that lunar colonists will cover their habitats with two or three yards of rock and rubble. It’s not as romantic as glass domes on the surface, but being able to actually survive a flare may take precedence over our preconceived notions of what a colony should look like from watching science-fiction movies.12

In a major flare, though, not just humans are in danger: our satellites can be fried as well. When an X-ray or a gamma ray from a flare hits the metal in a satellite, the metal becomes ionized. A very high-energy gamma ray can ionize many atoms in the satellite, causing a cascade of electron “shrapnel” to fly off the atoms. Remember, moving electric charges create a magnetic field. This sudden strong pulse of magnetic energy can damage electronic components inside a satellite (just as a magnet can damage your computer’s drive). The electrons themselves might short-circuit the hardware too.

Many civilian satellites have been lost in solar flare events. Military satellites are in many cases protected from this damage, and such radiation-hardened satellites can still operate even if there is a major flare. The effects of a nearby nuclear blast are similar to those of a flare, so these satellites may also survive a nuclear detonation in space (as long as debris and heat from the blast doesn’t get them).

Moreover, the Earth’s atmosphere absorbs the incoming high-energy light. While that protects us on the surface, the upper atmosphere can heat up from this and “puff up” like a hot-air balloon. If the atmosphere expands enough, it can actually reach the height of some satellite orbits. A satellite normally orbiting in a near-vacuum environment may suddenly find itself experiencing drag as it plows through the very thin extended atmosphere. This lowers the satellite’s orbit, dropping it into even thicker air, where it drops more, and so on. Even if it survives the initial flare, it may still be destroyed when it burns up in the Earth’s atmosphere! Many low-orbiting satellites are lost every solar cycle because of this effect. The American space station Skylab was destroyed this way in 1979.

Because of this, space agencies and commercial satellite owners watch for flares very closely. Flares are linked to the eleven-year sunspot cycle, tending to occur on or around the solar sunspot maximum, though for reasons still not well understood, the most energetic flares usually happen about a year after maximum. Incidentally, the 1859 flare, perhaps the brightest of all time, occurred a year or so before the sunspot maximum.

That flare induced quite a bit of magnetic activity on the Earth. While the flare itself probably did have some direct effect on the Earth, it’s now thought that it had some help.


Normally, there is a relatively constant flow of material from the Sun. Called the solar wind, it’s a stream of subatomic particles accelerated by the usual suspect: the solar magnetic field. The solar wind blows off the Sun in all directions, and continues outward for billions of miles, well past the orbit of the Earth around the Sun. Near the surface of the Sun, the particles can be seen as a faint pearly glow called the corona. The corona is incredibly hot—billions of degrees—but extremely tenuous, like a laboratory-grade vacuum. But over the trillions of cubic miles of solar surface, even something so diffuse can add up to a lot of mass. Astronomers think of the corona as the atmosphere of the Sun, so, in a very real sense, we live in the atmosphere of a star.

This has some disadvantages. Atmospheres sometimes have bad weather.

When a flare erupts from the surface of the Sun, needless to say, it tends to have an effect on its environment. The blast of energy and particles from the flare goes upward, of course, away from the Sun, but it also goes downward,onto the surface. This creates a seismic wave on the surface of the Sun with tens of thousands of times the energy of the strongest terrestrial earthquakes. The Sun’s surface ripples as waves of energy are slammed into it. The magnetic field lines surrounding the energy get an enormous jolt as well, and many times this is enough to disrupt them. The lines going in and out of the Sun’s surface in the area reconnect, release energy, and disrupt more lines around them. More and more energy is released as the effect spreads and more lines reconnect.

As this occurs, the matter that was previously constrained by those magnetic fields suddenly finds itself able to expand under the intense pressure. Instead of a single coil springing open as in a flare, it’s as if they are all free to expand. The matter suddenly bursts outward in a coronal mass ejection, or CME.13

The energy of a CME goes more into accelerating particles than it does into giving off light, so the event is actually difficult to detect initially. In fact, while the first flare was seen almost two hundred years ago, CMEs weren’t first seen until the 1970s!

However, their effect is profound. Unlike flares, which are basically a local disturbance, CMEs involve a gigantic area of the Sun. If flares are like tornadoes—local, intense, brief, and focused—CMEs are solar hurricanes. The effect is not as intense, but much, much larger: as much as a hundred billion tons of matter are hurled into space at a million miles per hour, and that can do far more damage on a far bigger scale.

As the CME expands off the surface of the Sun, it thunders across interplanetary space and expands to tens of millions of miles across. It creates a vast shock wave as it crosses the thin material previously ejected in the solar wind. It’s an interplanetary sonic boom, and it can accelerate subatomic particles to extremely high energy. These particles can gain so much speed that they move at a substantial fraction of the speed of light. It’s like a vast tsunami unleashed from the Sun, and it marches outward . . . sometimes toward us.

Once the CME erupts, it can cover the distance from the Sun to the Earth in one to four days. That’s all the warning we get.

It’s possible to see the actual event when it occurs. When you try to look at an airplane flying near the Sun, what do you do? You put up your hand to block the Sun, allowing you to see the plane. Astronomers do the same thing. They equip sunward-pointing telescopes with coronagraphs—generally very simple masks of metal that block the fierce light coming from the Sun’s surface—that allow fainter objects nearby to be seen. When a CME occurs, it can be seen by these telescopes as an expanding puff of light coming out from the Sun. If a CME is seen coming from the side of the Sun, astronomers breathe a sigh of relief: it will miss the Earth because it was aimed sufficiently far away from us. But sometimes the Sun is not so agreeable, and it sends a hundred billion tons of million-degree plasma screaming our way. This is seen as an expanding halo of light, because we are looking down the throat of an advancing front of subatomic particles accelerated to mad speeds.


On May 13, 2005, the orbiting Solar and Heliospheric Observatory captured this image of a CME heading right for Earth at 3 million miles per hour. When the wave hit, it caused a magnetic storm that spawned aurorae seen as far south as Florida.


When it gets here, all hell can break loose.


The Earth has a magnetic field that is similar in some way to the Sun’s. It’s probably generated by the motion of hot, molten rock and metal inside the Earth in a process similar to that which takes place in the Sun (with the Sun, though, the material is extremely hot gas), and is powered by a dynamo like the Sun’s field as well. This magnetic field extends past the Earth’s surface and reaches out into space, forming a region called the magnetosphere. If the Earth were alone in space, the field would surround our planet in a shape like that of a doughnut—the three-dimensional version of the crescent-shaped lines seen when you put iron filings on a piece of paper with a bar magnet under it. However, the constant stream of particles flowing past the Earth from the solar wind shapes the Earth’s magnetosphere into a teardrop shape, like water forming teardrop-shaped sand banks in a river. The pointy end always faces away from the Sun, and is called the magnetotail.

Most people are aware that the Earth’s magnetic field can be used to find north,14 but it also acts something like a protective force field, rebuffing any passing charged subatomic particle and sending it on its way. This protects us from the more severe effects of solar temper tantrums. It even protects our atmosphere: without the magnetosphere, the solar wind would have long ago eroded our air away, leaving the Earth a barren rock similar to Mercury. Mars probably lost most of its atmosphere this way as well.

So the Earth’s magnetic field is a good thing. Usually.

When a CME from the Sun reaches the Earth, it interacts with the Earth’s magnetosphere. The sheer energy of the flow can snap the Earth’s sunward-facing magnetic field lines, blowing them back around to the night side of the Earth into the magnetotail, where they can reconnect—it’s a bit like a stiff wind blowing your hair backward and making it all tangle up on the back of your head.

When the Earth’s field lines reconnect in the magnetotail, a lot of energy is released. Charged subatomic particles flow along the lines, down toward the Earth. Accelerated by the magnetic field, they slam into the Earth’s atmosphere, ionizing molecules in the air, stripping them of their electrons. When the electrons recombine with atoms, light is emitted with characteristic colors: oxygen molecules give off red light, and nitrogen green.15 Since this happens where the magnetic field lines of the Earth drop down into the atmosphere near the poles, in general people living at extreme northern and southern latitudes who venture outside during such an event are met with a brilliant display of aurorae—aurora borealis for the north, and aurora australis for the south. In a particularly powerful event, it’s possible to see them at mid-latitudes as well; the 1859 white-light solar flare event spawned a massive CME that caused aurorae to be seen as far south as Puerto Rico.

Aurorae have mesmerized people for millennia, and it was only recently understood that they are harbingers of vast unseen forces at play high above our heads, forces that trace their origins back to our nearest star and to the unimaginable violence wreaked there.

The effects of a big CME are far larger than a simple light show, however. For one, they compress the Earth’s magnetosphere. A satellite orbiting above the Earth inside the protective magnetic field may suddenly find itself exposed to the full brunt of the CME. The incoming radiation can then fry it.


The Earth is not the only planet affected by the Sun. This ultraviolet image from the Hubble Space Telescope shows an aurora at Saturn’s north and south poles. Any planet with a magnetic field can experience magnetic storms when the Sun is active.


There are even more profound effects from a big CME, ones that affect us directly, even on the surface of the Earth.

Remember that a changing magnetic field can induce a current? Well, when the magnetic field of the Earth changes rapidly because of a CME impact, any nearby conductor can suddenly find itself dealing with a huge surge of current.

There are plenty of such conductors on the surface of the Earth . . . like the entire North American power grid. Think of it: millions of miles of wires, all designed specifically to carry current from one place to another! Under normal operating conditions, these wires are easily able to carry a large amount of current, making sure that electricity generated at, say, Hoover Dam can be sent to Los Angeles to power someone’s margarita blender.

But these wires are very sensitive to solar storms. For one thing, these storms add a huge load to the system. For another, current heats up wires, causing them to sag. This process is well understood by electrical engineers and under normal operating conditions the system is designed to withstand it. However, a big pulse of current caused by a storm can add to the load already there, causing lines to heat up too much and break. For a third, over the years, more power generators have been added to the grid, but not more wires. As time has gone on, American power demands have grown. The wires were originally built to hold quite a bit of current, but in many cases they are operating closer and closer to their full capacity. A big surge can blow out the huge transformers vital to making sure the high-voltage electrical current in wires gets dropped to much lower voltages before going into your house. These transformers are expensive (some are as big as houses) and losing them can mean whole cities might go without power for great lengths of time.

Case in point: on March 6, 1989, an ugly and enormous group of sunspots rotated into view on the solar surface. Spanning 43,000 miles, they had already spawned many flares that were detected even though the spots themselves were on the far side of the Sun. Astronomers expected the worst.

They got it. Over a two-week period, Active Region 5395 blasted out nearly two hundred solar flares, a quarter of them rating in the highest energy category. At the same time, thirty-six CMEs were detected screaming out from the Sun.

Some of the effects were merely annoyances in the grand scheme of things. A microchip manufacturer had to shut down operations temporarily because some sensitive instruments were not behaving during the magnetic upheaval. Compass readings were off by many degrees, making navigation for ships difficult. Many satellites lost altitude—by as much as half a mile—and one military satellite could not compensate for the effects, and began to tumble. Other satellites were fried as well.

But the worst effects occurred on March 13, when a vast geomagnetically induced current was created by the storm. Voltage fluctuations caused power problems around the planet. In New Jersey, the current induced by forces far overhead blew out a power plant’s 500,000-volt transformer, which cost $10 million to replace. It took six weeks, and the company lost nearly twice that much money in lost power sales during that time.

In Quebec, the effect was much more serious. The current surge shut down a power generator, and the sudden loss of power collapsed the grid. Transmission wires failed over a huge area, some exploding in flames. In the middle of a winter’s night, the electricity for six million people in Canada was flicked off by the Sun. It took days to get the grid fully back up. Models of the event made by engineers estimated the total damage cost at several billion dollars.

As with asteroid impacts, there are ways to mitigate the damage done by flares and CMEs. Satellites can be designed to withstand particle and gamma-ray impacts, but at a significant cost to the manufacturer. The same is true for power grids; it would cost billions to retrofit power stations and add more power lines to accommodate another March 1989 event.16

Such events are rare, occurring two or three times per century. But as we make more demands on our power grids, the risk of potential damage from the Sun only increases.

And there is yet another direct impact from solar activity. Models of the impact of the 1859 event on our atmosphere have shown that the subatomic particles accelerated in the Earth’s magnetosphere by the event would have cascaded down into the atmosphere, breaking up (what scientists call dissociating) molecules of ozone in the upper atmosphere. Ozone is a molecule made up of three oxygen atoms (the molecule of oxygen we breathe has two atoms bound together), and is very efficient at absorbing the Sun’s ultraviolet light, protecting us from it. The amount of ozone depletion from the 1859 flare would have been relatively modest, just a few percent. However, that isenough to allow increased UV radiation to reach the Earth’s surface. The effects of this on humans are unclear because of spotty medical records from more than a century ago, but it’s possible there was a small but significant rise in skin disease in the years following the event. This increase in UV can also affect the ecosystem and food chain (see chapter 4 for more details on that than you want to know), though again the records from that time are incomplete.

There was, however, at least one measurable effect from the 1859 event. When broken up by incoming particles, the dissociated air molecules can recombine to form other chemical compounds, including NO2, or nitrogen dioxide.17 This reddish-brown gas, created high in the atmosphere, would wash down to Earth in rain and be deposited on the ground. Studies of ice cores from Greenland have shown an increase in the deposition of nitrates from that time.

The problem is, the NO2 can oxidize in the atmosphere to form nitric acid. When this dissolves in water droplets, acid rain can result, with terrible effects on the Earth’s ecosystem. This did not appear to be a major problem from the 1859 event, but if in the future more energetic eruptions impinge on our atmosphere, we may be able to measure the effects of that as well. That’s just another fun way the Sun can slam us.


With all this talk of magnetic storms, flares, and CMEs damaging the Earth, are we missing something more obvious? The Sun is, after all, far and away the major source of heat in the solar system. While the Sun seems rock-solid in its energy output, we have already established that it’s a variable star. Sunspots wax and wane on an eleven-year cycle; could this possibly lead to a change in the amount of energy we receive from the Sun? And if more or less sunlight hits the Earth, could that then lead to climate change on Earth, and a potential mass extinction?

It should be noted immediately that time and again, people have tried to tie the Sun’s eleven-year cycle with events here on Earth. The stock market, baseball scores, even personality traits have been (dubiously at best) linked to sunspot numbers. The problem is, if you look at enough cycles, some are bound to line up superficially. You have to be able to separate the wheat from the chaff, which can be very difficult.

Scientists have been arguing for years over whether there is some correlation between solar activity and weather on Earth. It seems that there is, but the factors involved are subtle and difficult to pin down. If they were clear, there’d be nothing to argue over. However, there are some connections that appear to be firmly in place . . . and sunspots do play a role. But the direction of that role might surprise you.

Sunspots are dark, cooler patches of the Sun’s surface. You might think, then, that if there are lots of sunspots, we get less light and therefore less heat from the Sun. So, lots of sunspots equals cooler climates.

But spots are only dark in visible light. There are bright regions surrounding sunspots called faculae (literally, Latin for “little torches”) that form because of the complicated connection between the Sun’s surface magnetic field and the hot gas bubbling up from deeper regions. The gas in the faculae is hotter, and therefore brighter. On average, sunspots are 1 percent darker than the Sun’s surface, but faculae are 1.1 to 1.5 percent brighter. This means that when the Sun is covered in spots, it’s actually brighter in visible light than it is when there are fewer spots!

The primary source of heat for the Earth’s surface is the visible light from the Sun. Studies have shown that when the Sun is at the peak of its cycle—when sunspots and faculae are more prevalent—the overall solar irradiation of the Earth increases by just about 0.1 percent. This is a small but significant increase—it causes a global temperature increase on Earth of about 0.1 to 0.2 degree Celsius (about 0.2 to 0.4 degree Fahrenheit). The opposite is also true; during the sunspot minimum, the Earth’s average temperature decreases by a fraction of a degree.

Let’s face it: this is a pretty small effect. By itself, it hardly changes anything on Earth. However, heating of the Earth’s surface from the Sun is only one way the climate can be affected. There are lots of other sources of climate change, as we are now all too aware. In many cases, these sources by themselves don’t do much to the climate.

But what if two or more of these effects add up?

Things can get bad. We need only to look back in time a short way to see how.

The existence of sunspots had been known for centuries, even before the invention of the telescope. But once telescopes were trained on the Sun, the view naturally improved. People have been monitoring the size and number of sunspots nearly continuously since the early 1600s.

In 1887, an astronomer named Gustav Spörer noticed that the records of sunspots appeared to show an absence of spots between the years 1645 and 1715. For literally seventy years, the Sun’s face was virtually blank, clean of solar acne. In the late 1800s, the scientist E. W. Maunder summarized Spörer’s findings and published them. We now call this period of sunspot deficit the Maunder Minimum.

All of this would be somewhat academic if not for one rather critical point: the years 1645 to 1715 were also a time of much lower than average temperatures across Western Europe and North America. It was so cold that the Thames River froze over (which it generally does not do, even in winter), glaciers in the Alps advanced, destroying whole villages, and the Dutch fleet was frozen solid in its harbor. This period was called the Little Ice Age.

It’s awfully tempting to directly connect the Maunder Minimum with the Little Ice Age, but we have to be very careful. In nature, it’s rare for a single effect to have a single cause, especially when the effect is as dramatic as a prolonged climate change. Usually, there are a number of events that have to occur to manufacture such a big change.

It turns out the Little Ice Age may have started long before the Maunder Minimum, even as early as the mid-thirteenth century. Caspar Ammann, a solar physicist who has extensively studied the connection between the Sun’s output and the Earth’s climate, notes that the Little Ice Age was not one continuous event, but instead consisted of “several pulses of cooling episodes . . . the first one started in the 1250s through 1300, after a medieval warming period.” Clearly, there were other causes of the temperature drop.

The biggest culprit is probably volcanic activity. There are clear signals of eruptions during the Little Ice Age, mostly seen in ice cores: atmospheric gases trapped in polar ice can be studied to determine what was happening in the Earth’s air during certain times in history. Interestingly, in the 1690s, the Little Ice Age got very severe, especially in Western Europe—there are stories of birds literally freezing to death sitting in branches. At this very time, there is a large spike in the amount of atmospheric sulfur found in ice cores, indicating large levels of volcanic activity. Volcanoes launch sunlight-reflecting dust and gases into the air, reducing the amount of visible light reaching the Earth’s surface. This cools the planet by lowering the amount of heat the surface can absorb.

By itself, this could not cause the severest parts of the Little Ice Age. But together with the Maunder Minimum, when the global temperatures would have dropped, it could have lowered the Earth’s average temperature even more.

Still, if this were a global effect, why was Western Europe hit so much harder than everywhere else?

It turns out there is a third player in this game. This gets a little complicated, so strap yourself in.

During a sunspot minimum, there is less solar activity in general. Besides there being less visible light, there is a drop in the amount of sunlight across the spectrum, including ultraviolet light. This turns out to be important: UV light is what helps create the Earth’s ozone layer; it turns normal atmospheric oxygen (O2) into ozone (O3). If there is less UV, there is less ozone. Ozone is actually quite important in the temperature balance of the upper part of the atmosphere, called the stratosphere. When there is lots of ozone the stratosphere is warm (because it absorbs UV light), and when there is less ozone the stratosphere is cooler.

Most, but not all, of the ozone creation happens in the tropics, at low latitudes near the equator. That’s because that’s the part of the Earth getting the most sunlight, and therefore the most UV. In the summer, ozone can be created both at the equator and at the pole, because that whole hemisphere is in sunlight. In that case, the difference in temperature in the stratosphere from pole to equator is minimal.

But in the winter, the pole is in darkness. No UV reaches the stratosphere, so no ozone is created there. That in turn means there is a big temperature difference in the ozone layer between the equator and the pole.

The problem is that the jet stream is sensitive to these temperature differences. In the winter, the temperature change across latitudes is large. This drives a strong jet stream, which circulates very firmly around the globe. But in the summer, when the gradient is smaller, the jet stream weakens. Instead of making a tight circle, it meanders, flopping down loosely to lower latitudes. When it does this, it can bring cold air from the Arctic to southern locations, and warm air from the south up to higher latitudes.18

As it happens, the jet stream tends to dip down more at certain locations on the Earth than others. Western Europe is one such place.

This then is the most likely scenario for the very bitter winter cold snap in the 1690s in Europe: volcanic activity dropped the global temperatures, as did the Maunder Minimum. Together they made things cold, but not brutal. But the drop in solar activity dropped the Sun’s ultraviolet output, which lowered ozone production on Earth. This changed the direction of the winter jet stream, bringing the unusually cold Arctic air down to Western Europe.

And then people could ice skate on the Thames.

It should be noted that in Western Europe, “the summers were not all that unusual,” according to Ammann. This indicates that whatever caused this intense pulse of cold weather was restricted to winter, which is consistent with the above series of events.

Like I said, this is complicated. But that’s the whole point. If it were simple, we’d understand it better, and no one would be arguing over how the Sun affects the climate. In fact, these events are all fairly well established in general, but the problem is the magnitude of each one. How much less ultraviolet light was emitted by the Sun during the Maunder Minimum? How much less ozone was created? How far did the jet stream dip south? How much sulfur was spewed into the air by volcanoes? Changing any one of these inputs makes the results different, so knowing how much each one affects the climate is very difficult to figure out.

The important thing to remember here is that while the Sun affects our climate, changes in its total output over the eleven-year magnetic/ sunspot cycle are small. There is a definite effect on the Earth, but it’s more like a priming charge than the explosion itself. It requires other catastrophic effects—volcanoes, asteroid impacts, man-made emission of CO2 and methane—to take advantage of the Earth’s climatic sensitivity and cause a disaster.19 And even then, at least in this particular case, the problems tend to be regional. The global environment of the Earth doesn’t change that much.

That’s cold comfort to people who are affected, of course. And if the particular region is very sensitive—or that region has global impact itself—then the results can be much worse. A decades-long series of brutal winters in the United States, for example, or China, could cause famine and economic depression. Wars start over such things, and modern wars can wreak far more damage than a simple solar minimum. When it comes to potential extraterrestrial sources of destruction, the last thing we need to do is add our own capabilities to them.

A more pertinent thought is: could another such minimum occur again? Yes, it could. Worse, it doesn’t look as if such events are entirely predictable. Scientists studying the occurrence of long minima in sunspot numbers show that they don’t appear at regular intervals, meaning they are not an inherently predictable phenomenon in the long term, although it’s marginally possible to make predictions about the very next sequence in the solar cycle. So we might be headed into another minimum a few cycles from now, or it might not happen for a thousand or ten thousand years. But it seems very likely indeed that it will happen again.


So if the Sun can indeed affect Earth’s climate, what about global warming? Is it caused by the Sun, and not by humans?

A lot of noise has been made on this topic, but scientists actually do agree on this: the Sun is not the cause of the current temperature rise seen in the latter half of the twentieth century to today.

This isn’t hard to show, actually. The amount of radiation from the Sun is measurable, and since the 1950s to today there has not been an increase in solar radiation. In other words, the Sun has not been getting brighter during the time when the Earth has been getting warmer. The amount of solar radiation has been quite steady since 1950, and is obviously not the cause of global warming. It’s clear to the overwhelming majority of scientists independently studying this phenomenon that it is human activity, our activity, that is behind the current sharp rise in global temperatures.

This most basic fact has not stopped some people from claiming that many other planets are also experiencing global warming, and therefore the cause here on Earth cannot possibly be human-induced. The only thing linking all the planets is the Sun, they say, and therefore the Sun is causing this warming.

However, this is nonsense. The claim is that Mars, Jupiter, Triton (a moon of Neptune), and even Pluto are warming.20 However, each of these has separate causes, linked with the individual objects’ atmosphere and orbit, and any purported warming is not related to the Sun.

And let’s be clear: these objects are much farther from the Sun than the Earth, and receive proportionately less heat. To warm up Pluto even one degree, the Sun would have to get so much brighter and hotter that it would be overwhelmingly obvious—in fact, the Earth would get totally fried. Since our own warming is less than a degree, it’s clear that the other planets’ warming must be due to some other source than the Sun.


We live on a small planet where a considerable number of factors have to align to make life hospitable. However, we live near a tempestuous star that will, inevitably, do what it can to disrupt that equilibrium. Ironically, too much solar activity can cause immediate and global damage, but too little can, in the long run, be just as bad. Like most things in the Universe, this is a delicate balance, and a swing to either side would be catastrophic.

However, we have survived many small oscillations. The Little Ice Age came and went, with people taking it in stride—they really did skate on the Thames. Huge flares have wreaked havoc on our power grids, and with a little care, foresight, and a pile of money, we can avoid total disaster.

As for the big swings . . . well, we’ll see. They may not happen for centuries or even millennia, and by then we may be able to take action. But the time to start thinking about it all is right now; and we are. Smart people are working on these very topics, and while it may take time to figure out all the angles, and there may be lots of arguments along the way, I think in the end we’ll figure a lot of this stuff out.

In the meantime, I’ll still enjoy the occasional sunny afternoon . . . but I’ll also be mindful that over my shoulder, just an astronomical stone’s throw away, is a vast and mighty star. And it has a temper.