Planetary tides during the Maunder Sunspot Minimum

Abstract

CONTROL of the 11-yr and longer cycles of solar activity tides raised on the Sun resulting from the gravitational pulls of the planets has often been suggested. Rudolf Wolf and R. C. Carrington were among the early astronomers who pointed out this possibility in the middle nineteenth century¹. The close coincidence of the sidereal period of gravitationally important Jupiter (11.87 yr) with the mean period of the observed annual sunspot means (11.3 yr) raises the possibility of such a relationship; the range of possible configurations of the other planets allows a wide realm of other tidal periods and effects. In daily sunspot numbers, a small but consistent periodicity at the sidereal period of the planet Mercury has been found², and a possible 178.7-yr period in sunspots (about twice the Gleissberg cycle) has been linked with multi-planet tidal influences³. Wood and Wood⁴ have applied a dynamical theory which includes all planets but Mars to reinforce their belief in a more than chance relationship. We reconstruct here Sun-centred planetary conjunctions and tidal potentials for the AD 1645–1715 period of sunspot absence (the Maunder Minimum). These are found to be effectively indistinguishable from patterns of conjunctions and power spectra of tidal potential in the modern era of a well-established 11-yr sunspot cycle. This places a new and difficult constraint on any tidal theory of sunspot formation.