An unexpected effect in solar cosmic ray data related to 29.5 days

Data relating to the detection of solar protons in the neighborhood of the earth (1952–1963) and to neutron counts (1958–1963) have been distributed on the basis of the mean synodic solar rotation period, 27.3 days, and the approximate synodic month, 29.5 days. In the latter, apparent departures from random distribution are especially marked. At the present time it is not clear whether the 29.5-day ‘effect’ is related to the sun or the moon or is only a statistical accident.