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What Is The Maunder Minimum?

written by: •edited by: RC Davison•updated: 7/22/2009

Imagine a thirty year period where a mere 50 sunspots were observed—compared to 40-50,000 we see in our own times. Weird, huh? This time period, known as the Maunder Minimum, has puzzled solar astronomers for decades—and has some powerful possibilities for climate change. Here's an overview:

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    When Was The Maunder Minimum?

    The Maunder Minimum took place in a time period from about 1645 to 1715. During this time, the Americas were being colonized, Europe was emerging from a more Medieval age, seafaring traders roamed the world—and virtually no sunspots were to be seen, fewer than ten a year, and sometimes none at all. This is to be compared to the thousands we see every year in modern times.

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    Deriving The Data: A History of the Maunder Minimum

    But where is this data coming from? Many people are somewhat loathe to trust any information that didn't come from our own century, seeing that modern instruments and modern methods weren't exactly available until, well, modern times.

    It was first noted by Edward W. Maunder, an astronomer during the later half of the 19th century and the beginning of the 20th. He came across it while going over old data, especially that of Gustav Spörer, a solar astronomer who took meticulous data during the time in question.

    This had largely been forgotten or actively ignored until brought up again by John A. Eddy in 1976—who was not the one to name this time period the Maunder Minimum, contrary to popular belief. Since then, the data has been poured over by hundreds of solar astronomers, bringing even more observations to light. History can be science, as studies on the Maunder Minimum have proved.

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    Spot The Maunder Minimum

    Yearly sunspots, 1600-2000. Credit: NASA.
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    Spörer's Law & 11-Year-Cycles

    Despite the low number of sunspots, the maxima of 11-year cycles could still be derived for this time period, showing that the Minimum did not mean any drastic change to the basic cycles of the sun.

    As defined by Spörer's Law—remember that name?—sunspot activity during the 11-year-cycle begins in the sun's high latitudes and drifts slowly down to the lower latitudes until a new cycle begins again in the higher latitudes. Though the data set is quite small, it appears that during the Maunder Minimum this held true—though mostly in the southern hemisphere of the Sun, as precious few sunspots even made an appearance on the northern hemisphere during this time period.

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    Ice Ages & Stradivari

    Some of the historians amongst you might have noted that those dates for the Maunder Minimum correspond pretty well with the Little Ice Age, a time period when the world was at its coldest since the big Ice Ages.

    Still, how could a lack of sunspots cool the whole planet down? There's a strong connection between the number of sunspots and solar energy. Some people theorize that, with less UV being emitted by the Sun during the Maunder Minimum, less would have hit the atmosphere and react with the oxygen there to form ozone—a greenhouse gas that keeps the heat in and the planet at a toasty temperature.

    For example, the luthier Stradivari, born a year before the beginning of the Maunder Minimum, made some of the most famously exquisite stringed instruments known to the music world. The connection? His instruments utilize a denser, more resonant wood, which grew the way that it did due to the cooler climate and thus slower growth during the Little Ice Age.

    However, fans of the Stradivarius series should not be thanking the Maunder Minimum quite yet. This is the subject of much debate. The Little Ice Age was mostly noted in the western and northern hemispheres, that is, in Europe and in the Americas and not so much in the rest of the world. Adjusting greenhouse gas levels, surely, would have effected the entire globe, though some scientists argue that it could have created more localized cooling by tweaking the jet stream and other currents. It's more likely that the Maunder Minimum contributed to the Little Ice Age, as opposed to being the sole cause of it. And of course, correlation does not equal causation, and it could be that the alignment of dates is a mere coincidence.

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    Estimated Global Temperatures During The Minimum

    Temperatures during the M. M. Credit: NASA.
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    Other Observations

    There are a number of other things that are suggested to be related to the Maunder Minimum, most of which are up for debate.

    Lower solar activity means lower levels of cosmic radiation, which in turn means lower lower levels of carbon-14—the amounts of which are critical for dating techniques. While the change isn't all that much—less than 1%—archaeologists take this minima into account while dating their finds.

    Additionally, this also effects the production of beryllium-10, which is used to analyze solar activity for events like the Maunder Minimum.

    It has even be suggested that the Sun may slow its rotation down somewhat during the Maunder Minimum.

    Auroras appear to have occurred just as much as they always do, without any marked abnormalities, indicating no apparent change in the solar winds.

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    Other Minima

    There have been other periods of low sunspot activity as well, though none as dramatic—or well observed—as the Maunder Minimum. Two recent examples of such minima include the Spörer Minimum took place between 1450 and 1540, and the Dalton Minimum between 1790 and 1820.

    Indeed, it is suspected that the sun spends at least a quarter of its time in such minima, though this obviously isn't provable until scientists have accumulated a few more hundred years of data to cement this theory, of our Sun and of others.