Though it has been in the sky for a while, for most of human history, no one was especially interested in looking very much — or at least very closely — at the moon. The Ancient Summerians took a quick look and decided that the moon was a God of wisdom called Nanna; for the Ancient Egyptians, it was a fertility god called Khonsu and for the Ancient Greeks, it was self-evidently a goddess called Selene, daughter of the Hyperion and Theia and sister of the goddess of dawn Eos and of the sun god Helios. Despite these conflicting certainties, the one thing that all traditional cultures were united on was the need not to study the subject any further. It is therefore hard to overestimate the significance of what happened on the night of the 30th of November 1609, when a hitherto obscure professor of mathematics at the university of Padua pointed his telescope up at the moon — and had the first open minded scientifically ego-less look at our earth’s natural satellite. Galileo Galilei had heard about the then astonishing new instrument called a telescope that had been produced in the Netherlands the year before and had found a way to grind lenses and produce a version with a 20x linear magnification. Through this optical marvel, he quickly realised that the old stories about the moon were nonsense. This was not the flawless marble like orb evoked in the Old Testament’s Song of Songs, nor the pearl evoked by Dante, nor the spiritual counterpart to the Virgin Mary dear to Catholicism. What Galileo’s telescope told him indisputably was that the surface of the moon was pitted and mottled. He concluded that the uneven waning of the moon must be caused by light occlusion from some very high mountains and extremely wide craters, which he assiduously drew with an accuracy that impresses to this day (he also estimated for the first time that the moon’s radius was 1,600km — not far off the 1,740km we know of now). It must have been tempting for Galileo to imagine that he was wrong. Everyone — from the Pope to his fellow academics to members of his own family — were sure that he was, and told him so with force. But Galileo went ahead and published a small book, Sidereus Nuncius (Starry Messenger) in which he insisted on his ideas — and also (to further consternation) threw in the suggestion that Jupiter had four moons rather than the presumed three. The story continues to speak to us because — though we may have little interest in astronomy — it mirrors a conflict that we all face between what the world insists is normal and true, and the sometimes diverging evidence of our own senses and suppositions. Galileo might have flouted public opinion in relation to the planets; we are more likely to run into opposition around marriage, work or politics. The issues will be different, but the strength of character the challenges demand will be identical. Much about social life conspires to keep us cowed and timid. Without being a crank or obsessive, by trusting reason and deduction, one of the iconic figures of early modern Europe prompts us to imagine how much madness and error might lie within what is innocently called common-sense.
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