Mark Grossman: The Sun “On Low” – The Maunder Minimum

27 February 2014

The sun goes through an 11 year cycle of activity.  What sort of activity?  Well, the sun quiets down to its “minimum” at the beginning of the cycle.  Then, it gets wilder as it builds up to its “maximum.”  Then, it goes back down to its minimum again.

The sun begins a cycle relatively quietly and, then, become more and more stormy.  Storms on the sun aren’t like storms on the earth.  When the sun has a storm, it gives off flares and coronal mass ejections (CME’s) — energy explodes off the sun’s surface and shoots out into space.  Few of these violent energy emissions come our way because the earth is, after all, a small target.

Sunspots go right along with the sun’s stormy cycle.  At the minimum of the 11 year cycle, the sun has the fewest spots and, then, as it builds toward the maximum, the number of spots increase.  Sunspots are cooler areas on the sun’s surface that seem to act like caps, holding down a lot of energy until the build-up explodes out from the surface in a flare.

Recently, concern has grown because our sun seems to be taking a nap.  Not only is it sleeping deeply, but it went to sleep awfully suddenly.  The cycle that began 2007 was expected to be the most active yet.  But the sun’s “activity” went down – way down.

Whether a real possibility or a scientific “urban legend,” the story circulated that the sun was “holding back.”  Its apparent quiet would soon be broken by a sudden burst of activity.  That didn’t happen.  Then, when the sun perked up the slightest bit in 2011, hopes rose.  But a dismally quiet 2012 ended with a new story. The story was that there would be a “double peak.”  So, even though the sun quieted down in 2012, it would soon return to its 2011 activity level and, then, burst into a period of even more activity in 2013.  The year 2013 came and went.  Sleepier than ever.

Has this happened before?

You’d have to go back just a bit more than a century to find a solar cycle as quiet as this one.  But there have been even quieter times.  The quietest of all was the Maunder Minimum – the lowest period of solar activity/sunspots in the 400 year history of sunspot counts.  And it was a long “minimum.”  During the period starting in about 1645 and continuing to about 1715 there were years without any sunspots at all.

The astronomers who actually observed the sun and recorded their observations during this grand minimum, John Flamsteed and Gian Domenico Cassini, did notice that they were seeing remarkably few sunspots.  However, it was only in 1894, with the benefit of hindsight, that astronomer Edward Walter Maunder drew attention to the period as including the lowest sunspot counts of any recorded.  Maunder’s fellow astronomers argued that these early astronomers had been sloppy in their observations.

Not until 1976, did American astronomer John Allen Eddy bring together all the available historical data and, supplemented with abundant physical evidence, demonstrated that Flamsteed and Cassini had been diligent and careful observers.  Eddy named this most minimum of minimums after the man who first noticed it, Edward Maunder.  So, the Maunder Minimum, as the low of all lows, remains as a sort of historical benchmark against which all declines in sunspots (and solar activity) are measured.

As our sun becomes increasingly quiet, it’s nice to know that something more extreme has happened at least once before.   But the current solar activity or, rather, lack of activity, is unique in many ways.  First, our current solar inactivity and low sunspot numbers are nowhere near the Maunder minimum level.   We’re currently working on the hundred year record, beating the low benchmark set in 1913.  But, the really distressing parts of the equation are the unknowns.

The amount of the decrease is less disturbing than the rate of decrease.  Although the number of sunspots is well above record lows, the speed of the decline has not been equaled in the last 10,000 years.  The worry is that, wherever this is going, it may be going there very quickly.

About 19 years ago, space satellites, without the interference of the atmosphere, were able to measure of he sun’s energy output.  Researchers were surprised to discover the sun puts out energy at a variable rate.  As sunspot activity declines, and the sun calms, it radiates less energy.  If you are an earth-based life form, the sun’s “energy output” means “heat.”  So, with such a sudden decline in activity, one has to wonder if the sun is cooling off.  And, if the sun is cooling, what does this mean for us.

Contrary to what you might think, small shifts in solar heat levels may not have a great effect on the earth’s temperatures.  In its natural orbit, the earth is closest to the sun in December of each year.  That proximity doesn’t lessen the intensity of winters in the northern hemisphere because the earth’s distance from its source of heat, the sun, isn’t the most important factor.  Rather, the angle at which the sun’s rays hit the earth – an angle that varies naturally with the seasons – makes the difference between summer and winter temperatures.  And, even though the heat of the sun goes up and down with increases and decreases in the number of sunspots, the changes in the sun’s heat output are quite small.

Even so, could the decrease in sunspots (and the heat of the sun) affect the earth’s temperatures?  No one is certain.  The Maunder Minimum did happen at the same time as what is called “The Little Ice Age,” but no one can be sure if the two were connected.  “The Little Ice Age” was a brief period of low temperatures.  The complete set of available data indicates that this century-long drop in temperatures affected the whole world.  But, one way or the other, we are not experiencing a decline in sunspot activity that is anything like the Maunder Minimum – the low of all lows.