SDO Solar Flare--the bright spot on the left--on March 7 2012. Credit: NASA/SDO

The first X-Class solar flare of the year went off on March 7th in spectacular fashion. Fortunately the flare went off where it's supposed to: on the Sun. Had this intense magneto-plasmic explosion gone off on Earth, we'd be toast; one of these releases an amount of energy on the order of 100 billion megatons of TNT.

Solar flares are highly energetic bursts of energy ignited by magnetically active regions on the Sun. Magnetic fields, generated by the motion of the Sun's hot, electrically charged gases, cause many of the Sun's more showy features, including the blemish familiar to most, the sunspot.

And yesterday, that's exactly what we saw from Chabot's observatory deck: a sunspot…and we didn't even need a telescope to see it! Let me explain. The active region that produced the powerful X-class flare only hours earlier left its mark on the Sun's bright complexion with a large cluster of sunspots—such an expansive cluster that it could be seen with the "naked eye."

Now, when I say naked eye, in this case I don't mean we were encouraging our visitors (mostly school kids at the time) to stare at the Sun directly. That would be pointless since the Sun is so bright at midday that it blinds us to any features we might see (and could blind us permanently if we look too long, even with sunglasses).

So, we have the kids look at the Sun through pieces of welder's goggle glass #14. It's a very dark filter—so dark that you pretty much can't see anything other than the Sun, or a welding torch, through it. This Sun-looking glass lets us peer safely into that wonderland in the sky, the solar disk, which ordinarily averts our attention by sheer brilliance.

Through the glass the Sun becomes a greenish disk, the same apparent size as the Moon. Most of the time, that's all we see: a glowing green disk in a sky of blackness. But even that is actually pretty awesome, and the sight routinely catches people by surprise.

Yesterday, however, the sunspot cluster marking the active region that produced the X-class flare was easily seen, unmagnified: a little dark spot on the Sun. And our eyes didn't even sting.

Now, a day after the flare, Earth is in the midst of a blast of plasma that was triggered by the flare activity, and a geomagnetic storm is in progress: the impact of an enormous bubble of plasma (electrically charged gas) that was blown in our direction has clobbered Earth's deflector screen, aka its global magnetic field.

Though the effects of a solar blast like this one and the geomagnetic storm it can produce usually go unnoticed by most, the event can cross over into our lives, if severe enough. Interference in telecommunications from atmospheric disturbance and even the rare power blackout caused by a magnetically induced overload of a power grid, have happened.

In space, satellites have been damaged by these storms, and astronauts on the space station generally take cover and wait them out. And closer to Earth's poles, lucky residents may be treated to a bright display of the Aurora—the Northern and Southern lights—as auroras are powered by solar activity.

We should expect more strong flares over the next year or so as the Sun proceeds through the peak in its current activity cycle, expected to climax sometime in 2013. I fully expect to view more "naked-but-protected-eye" sunspots, and to enjoy plenty of colorful movies of solar activity from NASA's Solar Dynamics Observatory (now on display in Chabot's telescope domes). Drop by Chabot on a sunny day and we'll put spots in your eyes.

The Sun seems to be unusually quiet these last few years– and solar scientists are excited by this long, deep slumber of activity because it is the first of its kind that has occurred since modern (space-based) solar observation began back in the 1960s.

The Sun is a huge ball of hot, electrically charged gas (plasma– mostly hydrogen and helium ions and electrons). Its constant internal motions of plasma– the rising and falling of convection cells, the non-uniform rotation of the Sun that involves a lot of twisting and sheering– generate magnetic fields, as any kid who has built an electromagnet might guess. In an electromagnetic, an electric current (moving electrons) generates the magnetic field.

The Sun’s magnetic fields can grow quite strong in areas, generated beneath the Sun’s visible surface (photosphere) and rising up through that surface and into the Sun’s enveloping atmosphere. At the photosphere, the magnetic fields tend to suppress the rising convection of plasma, choking the flow of heat from the interior to the surface and making spots that are less hot than the general surface (4000 degrees as opposed to 6000 degrees). The cooler spots are less bright, and we call them sunspots.

The same magnetic fields that leave their mark on the photosphere as sunspots rise into the solar atmosphere, where their sometimes violent twisting and interaction heats the gases there, and can power violent explosions such as solar flares and coronal mass ejections, both of which can affect the Earth.
So, sunspots are a visible sign of magnetic activity, and over the last 400 years of regular observations and counts of sunspots, a distinct 11-year cycle from one peak of activity to the next has been identified. Between peaks of activity (called solar maxima) are periods of relative "quiet," magnetically speaking, when there are few if any sunspots observed, and events like solar flares and such are not common.

We are currently in the midst of a solar minimum– the last solar maximum that occurred was around 2000/2001. But what has scientists buzzing right now is just how "deep" a sleep the Sun seems to be in. 2008 was the quietest year for the Sun on record since the beginning of the space age. Out of the 366 days last year, on 266 of them the Sun was completely spotless, which is well below "normal" for a solar minimum year.

What does it mean? Well– that’s difficult to say right now. Scientists are still trying to understand why the Sun experiences its 11–year cycle at all. And it’s not unprecedented; the Sun has experienced "deep minima" before. In 1913 there were 311 spotless days. Other deep minima have been seen in the sunspot record, and in almost every case normal solar activity returned; the next solar maximum is expected to peak in 2011 or 2012– perhaps 2013.

There is no indication that the Sun will remain quite and mostly spot free for an extended period– such as it did in the 17th Century, when the Sun remained quite for about 70 years!

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Magnetic activity on March 27th; white indicates N
magnetic poles, black S. Credit: ESA/SOHO/NASA.

A few blogs back I wrote about the 11-year cycle of ups and downs in solar activity–the Solar Cycle –and how over the last year or so the baton was supposedly passed from Cycle 23 to Cycle 24. But there has been an occurrence on the Sun that suggests we may be in somewhat of a gray zone….

For the past two or three years, the Sun has been downright boring. We set up our Sunspotter telescopes for visitors and try very hard to make what we see seem interesting–"See that perfectly blank circle of light? That’s the Sun! Really it is!"

About a week ago, the tedium was suddenly broken by a train of sunspots that rotated into view on Sun’s disk. Five–count'em– five sunspots! Finally, something to actually look at! And in the eyepiece of our Coronado Hydrogen-Alpha filter telescope there were filaments and plage! What are filaments and plage? Exactly! People wanted to know….

Then came the weird part: these were not Cycle 24 sunspots (I am not the Dread Pirate Roberts…); they were refugees from the supposedly defunct Cycle 23. While the distinction may be a fine point that doesn’t worry most of our visitors, it can still be a good talking point.

So, why were these five sunspots fingered as old solar trekkers rather than members of the next generation? It all comes back to what a solar cycle is–and sunspots, flares, prominences, and plage are merely details: manifestations of the Sun's magnetic convulsions. The Sun, like the Earth, generates an enveloping magnetic field–a big donut with a north and a south magnetic pole. On smaller scales there are plenty of twists and swirls and knots in the field caused by local "hot spots" of magnetic activity–which are what produce features like sunspots in the first place.

At solar maximum–the peak of activity of a solar cycle–the Sun's magnetic poles flip over, or reverse. In fact, it's this reversal that really lets us know when a solar maximum has arrived. (Earth's magnetic field also reverses polarity periodically–although this only happens every 200,000 years, on average.)

At the beginning of a solar cycle, new sunspot activity can be found at high solar latitudes, and as the cycle progresses, activity migrates toward the equator. On a finer nuance, the magnetic polarity of sunspots–which can be N or S, and are usually paired up, like the two ends of a bar magnet –are typically oriented east-to-west on the Sun's surface, one leading to the other as the Sun rotates. Which type of pole (N or S) leads and which trails depends on the overall magnetic "flip" state of the Sun's magnetic field.

To round out this report, the five surprise sunspots of yesterweek were lined up close to the Sun's equator, and the orientation of their magnetic poles bespoke their affiliation with the outgoing magnetic administration (Cycle 23). So far, only a single, high-latitude, reverse-polarity sunspot observed last January has signaled Cycle 24 .

Who knows? Maybe the magnetic candidates of Cycle 24 are still holding primaries, caucuses, and debates and have yet to begin some serious campaigning…

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

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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.

Extreme close-up of the Sun's visible surface,
showing 'bubbling' cells of convecting gas–each the size of
Northern California. credit: Hinode JAXA/NASA/PPARC

First things first: what is a solar cycle, and why is this one number 24? You've probably heard of sunspots and solar flares and disturbances in radio communications caused by solar activity, but had you noticed NOT hearing much about these things in the last two or three years?

The Sun exhibits a cyclic rise and fall in its level of magnetic activity. Being an enormous ball of roiling, circulating plasma (electrically charged gas), the Sun generates powerful magnetic fields in a way similar to how the circulating electricity in an electromagnet creates one.

Over the course of a solar cycle, the intensity and amount of magnetism generated by the Sun increases, like soup warming up on the stove, reaching a violent climax in which twisting, tangling magnetic fields break loose and release their energy in the form of solar flare explosions, coronal mass ejections, and tremendous heating of the solar atmosphere.

Sunspots are surface features formed by the presence of strong magnetic fields, and in general the number of sunspots that can be seen and counted indicate the level of magnetic activity on the Sun. For 400 years, since Galileo first started counting sunspots through his telescope, observers have kept track of sunspot counts, and over time a pattern in their number emerged. On average, the number of sunspot activity peaks every 11 years at a time called solar maximum.

I remember when I first started working at Chabot Space & Science Center, back in 1999/2000, during the last solar maximum. Using our Sunspotter telescopes on public observing days, in teacher workshops, and in my solar summer camp, we could easily count many sunspots-sometimes as many as 20 or more! Those were the days!

In the past two or three summers, however, it's a lucky week to spot just a single sunspot! Most of the time, the Sun's face has been a bland disk with few discernible surface features.

That status quo should start to change, now that we have allegedly reached solar minimum and are stepping onto the uphill slope toward the next maximum, which should happen sometime around 2011 or 2012. If you want to keep tabs on the rising solar activity, and you like lots of graphs and numbers and stuff like that, check out the Solar Cycle 24 website.

Oh, why is this Cycle 24? A 19^th Century astronomer who studied the then newly discovered sunspot cycle, Rudolf Wolf, established the cycle that spanned 1755 to 1766 as Cycle 1…and they've been counting up ever since.

But even in this "nap time" of the Sun, today's modern solar observatories and spacecraft, with their arrays of high-tech cameras and sensors, see plenty on the Sun to keep them busy.

Japan's Hinode spacecraft, launched in 2006, has returned libraries of amazing pictures and movies of solar flares, activity around sunspots, circulating hot gases, fine details of the life and times of magnetic fields…and all of this during solar minimum! I can't wait until the Sun really gets going and Hinode becomes like a camera-happy tourist in Tahiti….

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