Heavenly Bodies

We don’t know for sure where the names of the longest-known elements come from, but a connection was made early on between the most ancient metals and bodies visible in the heavens. Figure 1 shows an engraving from a seventeenth-century text with the title ‘The Seven Metals’ (translated from the Latin). It isn’t immediately obvious how the image is meant to depict seven metals until we explore the connections between alchemy and astronomy. However strange such associations seem to us now, we shall see that new elements named in the eighteenth, nineteenth, twentieth, and twenty-first centuries have had astronomical origins. We can’t properly understand why some of the more recent elements were named as they were without first understanding these earlier historical connections. As we look into the night sky, the distant stars remain in their same relative positions and seem to move gracefully together through the heavens. Of course, we now know that it is the spinning Earth that gives this illusion of movement. The imaginations of our ancestors joined the bright dots to pick out fanciful patterns such as the Dragon, the Dolphin, or the Great Bear—the latter being more often known today (with rather less imagination) as the Big Dipper, the Plough, or even the Big Saucepan. But, while these patterns, the constellations, remained unchanging over time, there were seven objects, or ‘heavenly bodies’, that seemed to move across the skies with a life of their own. They were given the name ‘planet’, which derives from the Greek word for ‘wanderer’ (‘planetes asteres’, ‘πλάνητες ἀστέρες’, meaning ‘wandering stars’). These seven bodies were the Sun, the Moon, Mercury, Venus, Mars, Jupiter, and Saturn, all of which were documented by the Babylonians over three thousand years ago. Until the sixteenth century, the most commonly held view was that the Earth was at the centre of the Universe and that the seven bodies revolved around the Earth, with the relative orbits shown schematically in Figure 2.