by Dario Camuffo
Abstract Popular beliefs on the effects of the Moon on the weather probably go back to when ancient civilisations followed a lunar calendar, and the Moon went from being a purely temporal reference to becoming a causal reference. The incoming heat flow on the Earth may vary slightly after solar activity. to and generate considerable effects. The light reflected from the Moon has also been hypothesised as a cause, but the associated energy is too small. The anomalistic period of the Moon (i.e., 27.5 days) coincides substantially with that of the sunspots found on the 17–18th parallel of the heliocentric latitude. Climatic modulation which lasts for around 27.5 days should be related to solar activity, which supplies energy with an amount of two orders of magnitude greater than the lunar-reflected energy. Another mechanism responsible for climatic variations is the redistribution of heat on the Earth. The Moon with the tides induces movement of the water masses of the oceans and with this there is a transport of heat. Semidiurnal lunar tides have been identified, although with modest impact, in the atmospheric pressure, the wind field and the precipitation. On a monthly time scale, variation of daily precipitation data shows that gravitational tides do indeed affect heavy rainfalls more than mean precipitation values. On the longer time scale, several authors have identified the 18.6-yr nutation cycle, which is clearly visible in several data analyses, but often it cannot be easily distinguished from the 19.9 Saturn–Jupiter cycle and the quasi-regular 22-yr double sunspot cycle which at times may be dominant. In the time scale of centuries, covering a number of periods with minimum solar activity, an analysis of meteorological data has demonstrated that only the Spörer Minimum (A.D. 1416–1534) was characterised by climatic anomalies., whereas the other periods had no singularities, or else the weak climate forcing was covered or masked by other factors, leaving the question still open. In practice, lunar and solar influences can be found and have been demonstrated with more or less the same level of confidence. Both have the same order of magnitude, and are generally weak, interacting, and being often masked by local effects.