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The Mystery of the Maunder Minimum

Today, we explore a curious solar phenomenon that occurred from 1645 to 1715.

As you may have seen or read, the sun is approaching its maximum activity in an on-going 11-year cycle. This is observed by increases in solar flares, prominences, ejections of charged particles, and … sunspots. Sunspots are a key measure of solar activity.

Sunspots were observed on the sun as early as the 4th century BCE. However, sunspot measurement first began with the invention of the telescope in 1608. An image of the sun would be projected through a telescope onto paper, allowing the sunspots to be measured. This measurement continues uninterrupted today, although the methods are much more sophisticated.

Over the centuries, the data revealed that solar activity has an 11-year cycle from minimum to maximum and back to minimum. However, in the late 19th century, several scientists noted the prolonged solar minimum that occurred in the sunspot data from 1645 to 1715. This became known as the Maunder Minimum, named after one of the scientists. More generally, it became known as a ‘grand solar minimum.’

To some extent, the Maunder Minimum coincided with an extended period of low temperatures in northern Europe, known as “The Little Ice Age.” There has been supposition that the slow solar activity of the Maunder Minimum produced these low temperatures. However, the current theory now is that the Little Ice Age was the reduction in solar energy reaching the Earth due to dust caused by volcanic activity. While the sun obviously has a major influence on weather, there is little evidence that changes in the sun cause climate change. However, research continues.

Considerable research has been focused on the Maunder Minimum, using more detailed analysis of the sunspot numbers, auroral intensity, isotope analysis of ice sheets and tree rings. Some studies indicated that the solar activity during that period was not unusual, and that sunspot count methodology was flawed. However, other studies suggest that the low solar activity was real. There may have been as many as 27 ‘grand minima’ in the last several thousand years.

Even today, the Maunder Minimum remains somewhat an enigma in solar astronomy.

This episode was produced by the Bryan Cashion, Black Canyon Astronomical Society and KVNF Community radio.