The Behaviour of Solar Activity as Inferred from Sunspot Observations 165 BC to 1986

Abstract

We have studied the behaviour of solar activity on the basis of a catalogue of non-telescopic sunspot observations covering the period 165 BC to 1684 (Wittmann and Xu, 1987), to which recently has been appended a catalogue of naked-eye sunspots of the period 1764 to 1986. Our main results are as follows: between AD 302 and 1980 there are 44 conspicuous maxima which may be expressed as: Year (Max.) = 4.0 + 11.116xN (where N - 178 for the maximum of 1981, i.e. N = Zürich cycle + 157). The residuals (0-C) are less than 3 years in most cases, and only one (in 1790) slightly exceeds 4 years. The average period of the sunspot cycle is P = 11.116 ± 0.007 years, with individual periods ranging from 7.5 to 14.5 years (30% are between 10.5 and 11.7 years; 70% are between 9.9 and 12.3 years). While both the ‘modern’ and the ‘reliable’ ancient spots show a bimodal distribution of 0-C values with a distinct concentration around zero, the residuals for the whole sample of ancient spots show only weak indications of a maximum and are almost evenly distributed (which we interpret in terms of a statistically incomplete sample, rather than as evidence for a strange attractor model of solar activity). Whereas the Oort Maximum of AD 1130, the Wolf Maximum of AD 1380, the Spoerer Maximum of AD 1600 and the associated minima preceding them by about 90 years (viz. the Oort Minimum 1010–1050, the Wolf Minimum 1282–1342, and the Spoerer Minimum 1416–1534) are conspicuous in our data (as are several other intervals characterized by a scarcity of observations), there is little or no indication of the Maunder Minimum (1654–1714) from our data alone. The Maunder Maximum of AD 1780 is again conspicuous, but this time in the modern sunspot record.