The Sun: Not So Boring

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Apr 16

2011

by GAMBlog

As an ex-solar physicist, I've been watching the sun with fascination as its activity predictably ebbs and flows over an 11-year cycle. However, in recent years, our nearest star has delivered some surprises.

In May 2009, I jokingly remarked in a Discovery News article that the "sun is being really boring." This was in response to the extended solar minimum that had turned our usually dynamic and explosive sun into a spotless, quiescent disk.

Back then, the sun's lull had extended to 18 months after the start of Solar Cycle 24. Today, the sun is exploding with activity, crackling with solar flares and blasting the Earth's atmosphere with energetic plasma.

Earlier this year, the sun unleashed two "X-class" solar flares, the most powerful X-ray emitting flares the sun can produce. The last time we saw one of these was back in December 2006 when the previous solar cycle (Solar Cycle 23) was coming to an end.

In March, solar observatories also saw an immense coronal mass ejection (CME) blast a billion tons of plasma into space, some of which hit our atmosphere, creating a beautiful auroral display in our atmosphere.

Image: The Feb. 15, 2011 X-class solar flare as imaged by
NASA's Solar Dynamics Observatory (SDO).
Credit: NASA/SDO, AIA, EVE, and HMI science teams.

So, solar physicists are getting excited. We are approaching solar maximum (expected around 2013) and there are a lot of solar fireworks to come.

"Finally," exclaimed Richard Fisher, head of the Heliophysics Division at NASA Headquarters in Washington DC, in a recent NASA article, "we are beginning to see some action."

Despite its blank stare three years ago, the sun was anything but boring. The very fact that there had been so few sunspots, flares and CMEs was cause for great interest – why was the sun being so quiet? Granted, it was going through an expected solar minimum, but this minimum went on far longer than anyone expected. And therein laid a mystery: What is happening inside our sun?

You'd think that having a stellar laboratory a mere 150 million kilometers away (or 1 Astronomical Unit) we'd know everything there is to know about that massive, searing ball of plasma. Alas no, there are many mysteries that still allude modern science, and many of these mysteries are driven by the powerful magnetic field dominating our star.

Through the use of sophisticated space and ground-based observatories, we know that the root mechanism driving the sun is magnetism. Over its approximate 11-year cycle, when the sun slowly builds in activity from solar minimum to solar maximum, you can actually see the inner turmoil bursting through the solar surface.

At solar minimum, solar magnetism is at its least-stressed state. But as the sun rotates faster at its equator than at its poles, the solar magnetic field is "wound up" like a stressed elastic band being wrapped around a ball. As the 11 years advance, magnetic stress increases and magnetic field lines start popping through the sun's surface. As they do this, the hotter surface plasma is pushed to the side and in spots, we start seeing the sun's cooler interior.

These spots are known as "sunspots," and because they are related to magnetic activity, we have a means of studying the sun's inner dynamics. They are also a great indicator as to where solar flares and CMEs may be launched from. The best thing about sunspots is that you don't often need sophisticated hardware to see them – astronomers for thousands of years have been keeping count of them by eye, allowing modern astronomers to look back at historic records and compare them with today's sunspot activity.

When looking at the "sunspot number" throughout history, there are some odd quiet periods. The "Maunder Minimum" (from 1645 to 1715) and the "Dalton Minimum" (from 1790 to 1830) were periods when the numbers of sunspots recorded were low. There are many theories as to why this might have occurred -- perhaps the sun has longer-period cycles when magnetic activity calms dramatically?

When the sun had its extended sleep over the past three years, there were some murmurings that we could be entering another long "quiet period," but that wasn't to be. Our nearest star is waking up and the delayed Solar Cycle 24 is back on track with an explosive 2011.

But will the 2013 solar maximum be as active as the last one? Some predictions suggest it will be less impressive, others say it will be "about average." At the moment, we can only guess – I suspect it has a few more surprises in store.

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Blogger  :
Dr. Ian O'Neill, a Space Producer and science writer for Discovery News. Before working for Discovery News, he was a solar physics researcher at the University of Wales, Aberystwyth, UK where O'Neill carried out numerical simulations of coronal loop heating mechanisms.