The Solar Activity and Antonio Stradivari
The Sun is not a common star as we normally are used to consider it, at least not in that sense. If we are here it is above all thanks to it and its “calmness”, as it is also the star that has allowed us to understand all the others: it is in fact the most studied star ever thanks to the fact that it is so close that its surface details and atmosphere are also visible to the naked eye (using appropriate filters).
Today we know that it has a cycle of about 11 years (sometimes 10 to 13 times) during which it passes from a maximum (period in which there are many sunspots and flare) to a minimum (they also spend weeks between a spot and the other) and then return to the maximum. The Sun is therefore a stable star, it is not as capricious as red dwarfs or “bipolar” as some variables, but are we sure of this? Just over 400 years of solar observations are enough to keep us quiet?
Between 1645 and 1715 the Sun took a “break”, its activity fell well below the minimums known today, but how do we know? Edward Maunder, a British solar astronomer who lived between 1800 and 1900, studying the observational chronicles of the time realized that during this period few hundred sunspots were registered against the 130,000 expected. But what exactly happened in that time span known today as “Maunder’s minimum”? What emerges from the observations is that the eleven-year cycle disappeared leaving our star always at the minimum. But why did the Sun “fall asleep”? Probably it is a cycle that is added to that of 11 years and the cause could be a temporary expansion and slowing down in the rotation of our star. Carbon 14 and beryllium 10 can help us to understand more: in fact these are isotopes whose presence is closely linked to solar activity and by studying their concentration in trees and polar ice we know today that in the last 1200 years the Sun has met 4 big lows:
- Minimum of Oort (1010-1050)
- Wolf’s minimum (1280-1340)
- Minimum of Spoerer (1420-1530)
- Minimum of Maunder (1645-1715)
Of all, the last one was the one characterized by almost no solar activity and the period coincided with the coldest part of the small ice age, a period in which in Europe the average temperature dropped by a few degrees favoring the advancing of the glaciers (on the Alps they even incorporated whole countries) and several rivers froze: on the Thames there were real fairs on the ice! Colder winters and less hot summers made the trees grow stronger by reducing photosynthesis and giving rise to more compact wood: also the Balkan maple and the Val di Fiemme spruce with which Stradivari “worked”, then a little ‘of the magic of those instruments is due to our Sun and its “rest”.
A final curiosity: carbon14 and beryllium10 also tell us that the increase in solar activity from the end of the Maunder minimum to today is the most intense of the last 9000 years.
In the graphs: the number of sunspots per period that highlight the Maunder Minimum and the variations of atmospheric carbon14 in the last 1200 years