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Maunder Minimum

2 September 2016

William Thompson provided a nice link to an article by John A Eddy in Science journal 192 (4245) June 18th 1976, that is still worthwhile reading and digesting nowadays as we have a fairly quiet sun and some people are predicted an even quieter sun in the next solar cycle. These last eleven years (roughly) and are watched and catalogued by astronomers in order to see if a pattern exists. Go to www.streamlinepresenter.com/Cosmoclimatology/pdf/Document_d_2/Maunder%20…

Between 1645 and 1715 solar activity was extremely low. The article proceeds to outline the history of sun spot observations and the prevailing mainstream position in 1976. Some interesting correlations emerge as we are in the era of Milton and Newtone for example and the reign of Louis XIV, 1643-1715 actually covers the whole of the minimum event. Astronomical telescopes were in common enough usage right across Europe, from Britain to Poland and from Italy to Spain. They were probably available in Russia too but this is not mentioned by Eddy. During the 70 year period the Greenwich and Paris Observatories were founded and Newton developed the reflecting telescope (and so on). Hence, the equipment to observe was technologically advanced and was available commercially for anyone to purchase. 

Sun spots at that time were thought to be clouds drifting across the face of the sun so how seriously were sun spots recorded. Was it half hearted – subject to personal whim. Eddy goes through this dilemma in a diplomatic fashion and then says that aurorae are more reliable as evidence of activity on the sun (unknown in the 17th/18th centuries) and there is quite a lot of recordings of auroral phenomena. He shows the period 1645 to 1715 was characterised by a marked decline of aurorae. Far fewer are recorded in those 70 years than in the periods before and after.

He also says the history of C14 in the earth's atmosphere can also determine levels of sun spot frequency and solar activity (as cosmic rays are modulated by solar activity). When the sun is quiet galactic cosmic rays increase and the C14 proportion of the atmosphere rises – so if there had been a lull in solar activity one would find evidence of that in tree rings (as an example). In fact, the first major anomaly in early studies of C14 history was earmarked by a prolonged increase in cosmic rays which reached a peak between 1650 and 1700 (smack bang in the centre piece of the Maunder Minimum).

Eddy then moves on to solar eclipse data – and Newton's observations. It seems that any suggestion that sun spots were less visible as a result of clouds or other atmospheric phenomena is untenable and Eddy says he can find nothing that actually contradicts Maunder – and much that supports him. Therefore the idea that the sun is a constant as far as activity is concerned must be wrong. The question of whether solar activity = warming, and low solar activity = cooling, is something else (but one can see how the idea germinated into a generally accepted point of view as the 1600s are classified as the Little Ice Age).

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