1. INTRODUCTIONThe horizon motions of the sun and the moon, and especially their extremes, are well attested as targets for alignments of archaeological sites since prehistoric times, for many cultures across the globe. Monuments such as Newgrange and Stonehenge have their main axis oriented towards the solstices whereas others, e.g. the temples in Malta, also exhibit alignments with the equinoxes.1 Proponents of lunar alignments tend to focus on the lunar extremes, the so-called lunar standstills. Clive Ruggles's comprehensive survey of British and Irish megalithic monuments shows a preference towards such orientations, and many other cases, within megalithic Europe and outside it, abound.2On the other hand the significance of other, non-extreme, astronomical events involving the sun and/or moon are well attested by the ethnographic and historical records. Examples include zenith and anti-zenith sun and moon.3 In fact, smallpopulation non-literate contemporary peoples often have a much deeper connection to, and understanding of, the movements of the heavenly bodies than had been previously assumed, even when such is not immediately discernible in their material culture.4 It is therefore very possible that prehistoric peoples were well versed in the position and movements of the luminaries and would perceive something Westerners have yet to notice. The fact that lunar standstills seem to have eluded astronomers for millennia until Alexander Thorn proposed them as targets for certain megalithic sites in Britain potentially indicates that other such cases might abound.Da Silva5 proposed the notion of crossover to account for Thorn's orientations towards a 'megalithic equinox'. Thorn discerned some intentionality in British megalithic monuments to 'miss' the equinoctial marker at 90° of azimuth. Da Silva noted a crossover between the rise positions of the sun and full moon, which occurs around the equinoxes, and used ephemeris simulation to get predicted distributions for this spring full moon. It was found that the predicted peak for the spring full moon was at an azimuth of 97.3° (a declination of -5.7°), which would account for the distribution of orientations of megalithic dolmens in Alentejo, Portugal.Improved simulations were later developed by Pimenta,6 who found the main axis of the megalithic enclosures of the same region to be aligned to the autumn full moon. These simulations were commented and expanded upon by Silva,7 who coined the generalized term 'equinoctial full moons' (hereafter EFMs), and showed that two groups of dolmens in Central Portugal, previously interpreted as having sunrise alignments, actually exhibit the expected EFM peaks in their histograms. The fact that EFMs are 'distribution type events', with highly non-Gaussian distributions, was also discussed.In this paper the notion of crossover is shown in a new light and expanded upon in the hopes that such astronomical targets might in future be considered by archaeoastronomers and ethnographers. Crossovers are now understood to be observable for all lunar phases but, as ethnography and history tell us, the most significant phases were the full moon and the dark or the crescent moons, and so the focus is on these. Algorithms for ephemeris simulation have been developed and the logic behind them is explained in Section 2. In Section 3, the declination and chronological distributions for all crossover events are shown and analysed. These form the basis for interested cultural astronomers to compare these distributions to their own data. Section 4 presents some preliminary case studies using data available in the literature. The paper concludes with a review of the findings and the impact they potentially have on alignment interpretation. In this last section an alternative interpretation for minor lunar standstill alignments is proposed in light of the findings.1.1. Horizon CrossoverTo understand what the crossover is, one has to be aware of the positions of the sun and moon in the sky, relative to each other, throughout the year. …