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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