M9 Solar Flare of January 23 2012; credit: Solar Dynamics Observatory

Let's see, what's the weather like right now (sticks finger into the air). Speed, 1.2 million miles per hour, density 1.1 protons per cubic centimeter, temperature 200,000 degrees Celsius. Sound a bit extreme? Surely climate change hasn't made things THAT batty. As a matter of fact, conditions have calmed down in the last several hours.

Okay, I'm not talking Earth weather—if I were, we'd all be dead, fast. I'm talking space weather, and a subsidence in its condition following a powerful solar flare whose ejecta struck Earth on Tuesday, causing a strong geomagnetic storm, and some pretty Northern and Southern Lights.

The flare in question, associated with the big sunspot numbered 1402, erupted on January 23rd, launching a coronal mass ejection–a "cantaloupe" of plasma that makes Earth look like a grape. Rated as an M9-class flare, it packed umph just shy of what's necessary for adult "X-class" flaredom, the most power kind.

When it reached us the megablob of plasma struck Earth's magnetic field, causing the geomagnetic storm and a minor list of annoyances (communications interference, for the most part, and some reported concern to an electrical grid operator). On the showier side of solar activity, the storm generated spectacular auroras in high latitudes.

The Sun's magnetic activity—the source of disturbances like flares and oft-associated coronal mass ejections—has been on the rise for the last couple of years, heading for a forecasted peak in activity ("Solar Maximum") in 2013. We're in "storm season," with respect to the Sun's 11-year magnetic activity cycle, so we can expect more, and stronger, flares and geomagnetic storms in the next year or two to come.

Back when I was growing up (1960's) I learned that space is a vacuum, void of the gases we find in Earth's atmosphere. It was a stark picture of emptiness, at least as this child comprehended the data. Sure, sunlight and starlight streams through that vacuum, but other than that, Dr. Science explained, if I took one space-step outside of my personal Mercury space capsule without protection, I'd suffocate and my blood would boil and freeze at the same time—not to mention that I'd get cooked by the dangerous ultraviolet and X-ray radiation shining from the Sun.

Okay, close the Time-Life science series book entitled "Space" and open an astrophysics textbook of my 1960's youth era, and I would have learned that there's more to the vacuum of space than nothing.

Our Sun, a gargantuan fusion bomb that consumes a mass of hydrogen comparable to that of the entire human race each second, continually spews more than just sunlight into the space around it. Hot, electrically charged gas (plasma), mostly hydrogen nuclei and electrons, blended with an accompaniment of magnetic fields, blow outward from the Sun's surface and atmosphere all the time.

That's the solar wind, and its conditions, whether normal or stormy, is what makes space weather. So when you're curious about the weather conditions in the space surrounding Earth and its protective magnetic field, poke your finger skyward and extend your arm—oh—about 50,000 miles…or just go to a space weather website like Spaceweather.com.

Illustration of a blast of solar wind impacting
Earth's protective magnetic field. Credit: NASA

Did you know that the Sun also has an atmosphere, and that the Earth is inside it? In fact, the Sun's envelope of gases extends well beyond the orbit of Pluto, out to the regions of the solar system where the 3-decade-old Voyager spacecraft are only now reaching.

"Space weather" refers to the conditions in space caused by the outflow of electrically charged gases (plasma) coming from the Sun—what we call the "solar wind." The term "space weather" may conjure images of cosmic tornadoes, astral lightning bursts, and some Star Trek version of a galactic hurricane– but actual space weather is nothing so Earthly and familiar.

First of all, the "air" in space is nothing like the atmosphere we draw our breath from. Earth air, at the surface, is made of nitrogen, oxygen, argon, carbon dioxide, water vapor, and other trace elements, and is relatively dense. "Space air" is mostly hydrogen– ionized hydrogen at that (meaning stripped of its electrons and so electrically charged; the separated electrons are also blowing along in the solar wind).

Second, the gases of the solar wind are extremely rarified. Despite the talk of a solar atmosphere, solar wind, and space weather, space within the solar system is still almost a complete vacuum. At Earth's distance from the Sun, the average density of the solar wind is somewhere between 6 and 9 atoms (mostly hydrogen) per cubic centimeter. If you spread out the gas contained in an ordinary party balloon to this same thinness, it would fill a volume of space over 10 miles across!

Third, the solar wind, for all its sparseness, blows fast! Depending on conditions of space weather, the flow of solar wind past the Earth can speed along anywhere from 200 to 900 kilometers per second! Earth's fastest winds slug along at only a few hundred kilometers per HOUR.

So how does space weather—the changing conditions of the solar wind—affect us on Earth? How might you, personally, have experienced, directly or indirectly, the effects of the Sun's gentle breeze?

The most familiar phenomenon caused by space weather is Earth's beautiful auroras —the northern and southern lights. Interactions between the solar wind and Earth's magnetic field and electrically charged particles trapped in it excite atoms in the upper atmosphere to emit light. And it's not just a softly glowing night light: the most powerful auroras can generate up to a trillion Watts of power!

Solar wind "storms" can not only produce more active auroras, but can cause fluctuations in Earth's magnetic field whose effects can be felt on the ground. These "geomagnetic storms" usually pass unnoticed, perhaps causing a tiny change in the direction that compass needles point– but have also been known to overload electrical power grids and cause blackouts.

In the space around Earth, solar storms have been known to damage or disable satellites, and can put unprotected astronauts at risk. Space walks on the International Space Station are scheduled for times when space weather is – so to speak -"sunny and calm."

Thinking about space weather on Earth might seem like worrying over Atlantic hurricanes here in the Bay Area—but with more and more human activity taking place beyond the confines of our atmosphere, this is a very real and vital concern, and is taken very seriously.

Benjamin Burress is a staff astronomer at The Chabot Space & Science Center in Oakland, CA.