A post by Rare Books Curator Dr Danielle Westerhof
Imagine gazing at the stars and discovering something that utterly shatters long-held ideas about the universe and our place within it. A realisation that we are not as significant as we thought we were and that there is more – much more – to the heavens than we thought we knew.
This is what happened to the Italian scientist Galileo Galilei in the early years of the seventeenth century when he began to study the skies using a recently invented instrument. Night after night, as he observed the moon’s surface and other celestial bodies, with a telescope he had worked on for months to improve the original Dutch design of, Galilei came to the startling conclusion that the heavens were not as perfect as everyone up to that point had believed. In early 1610, he published is findings in the Sidereus nuncius, or ‘Heavenly messenger’, a slim tract that had a lasting impact on how we view the world today.
Except for one sixteenth-century astronomer and philosopher, Nicolaus Copernicus, who had postulated a theory about a heliocentric (that is: sun-centred) and ever-changing universe, most early modern astronomers stuck with the traditional view that the heavens revolved around the earth in divine harmony and perfection (geocentrism).
Galilei’s observations showed that the moon’s surface was full of mountains and valleys of irregular shape. More significant was his observation that Jupiter had its own moons. These we now know individually as Io, Europa, Ganymede, and Callisto, but in honour of his patron Duke Cosimo de’ Medici, Galilei named them ‘Medicean stars’ (Medicea Sydera) after the four Medicean brothers.
For the first time, Copernicus’s theory of heliocentrism, which had gained little traction outside a small circle of fellow philosophers and scientists, was supported by observable evidence. Even Church authorities could not ignore the independent proof of Galilei’s discoveries provided by the astronomers of the Jesuit College in Rome. Although the Sidereus nuncius was not banned by the Church, Galileo was not so fortunate with his second book arguing in favour of heliocentrism and he was forced to renounce his theories towards the end of his life.
Although we now know that Galilei’s theory was not completely correct, his work helped to lay the foundation for scientists like Isaac Newton to develop his laws of motion and gravity.