Galileo's telescope reaches 400th anniversary
It is 400 years since Galileo Galilei demonstrated his telescope, which would lead him to make new astronomical observations
Galileo's telescope helped the astronomer to learn more about our solar system. This is a reconstruction of the telescope. Photograph: Jim Sugar/Corbis
While many people have been loudly celebrating this year's double commemoration of 200 years since Charles Darwin's birth and 150 years since the publication of On the Origin of Species, another scientific anniversary has crept up relatively quietly, marking an event which arguably changed human thought and the way we see ourselves even more irrevocably.
Exactly 400 years ago today, on 25 August 1609, the Italian astronomer and philosopher Galilei Galileo showed Venetian merchants his new creation, a telescope – the instrument that was to bring him both scientific immortality and, more immediately, a whole lot of trouble.
A refinement of models first devised in the Netherlands, Galileo's slim, brown stick was puny even by the standards of something one might buy in hobby shop today. But his eight-powered telescope, and the more powerful models he soon produced, when pointed skywards led Galileo to a series of groundbreaking conclusions.
The moon was not, as long believed, completely smooth. Another planet, Jupiter, also had moons. Meanwhile Venus showed a range of moon-like phases, something which could not happen if both it and the sun orbited the earth.
This latter phenomenon had been predicted by Nicolaus Copernicus when, nearly a century before, he had proposed the notion of a planetary system with the sun at the centre, not the earth.
Galileo's discoveries were, perhaps predictably, not best welcomed by the Catholic church, and he spent the final decade of his life under house arrest.
It was certainly a revelation which upset the orthodoxies – and the churches – at least as much as Darwin's, and perhaps merits a bit more of fuss, although museum-goers in Philadelphia and Stockholm can view one of Galileo's very early telescopes, on loan this year from Florence. A good deal more people are likely to be alerted thanks to Google's day-long adaptation of their main page logo to a Google Doodle in honour of the event.
The Telescope
The diagram of the optical principles of the telescope from Sidereus Nuncius.
Image by kind permission of the Master and Fellows of Trinity College Cambridge.
The story of Galileo's telescope is well known, as he recounted it himself in the Starry Messenger. In July 1609, Galileo was in Venice, when he heard of an invention that allowed distant objects to be seen as distinctly as if they were nearby. In October 1608, a Flemish spectacle-maker by the name of Hans Lipperhey had already applied for a patent (which was refused), and news of the gadget was widespread in Europe by the time Galileo had heard of it. Around the same time, a foreigner turned up in Padua with the instrument; Galileo rushed back to Padua, only to learn that the foreigner had gone to Venice to sell his instrument. Galileo's friend, Paolo Sarpi, had advised the Venetian government against purchasing the instrument from the foreigner, since Galileo could at least match such an invention. By then, Galileo had worked out the principle of the telescope and returned to Venice himself with an eight-power telescope. The Venetian government doubled his salary, though Galileo felt that the original conditions were not honoured.
Galileo gradually improved the power of his telescope, grinding lenses himself, and began observing the heavens. In the first two months of 1610, he was writing The Starry Messenger, and by 12 March, the book was already printed at Venice, dedicated to Cosimo de' Medici. Galileo continued his observations with his telescope, some of which he conveyed in ciphers to Johannes Kepler, who had already responded enthusiastically with the Conversation with Galileo's Sidereal Messenger. Galileo's discovery of the 'handles' of Saturn was encoded in 'Smaismrmilmepoetale umibunenugttavir as', which could be unscrambled as 'Altissimum planetam tergeminum observavi': I have observed the highest of the planets three-formed. Kepler deciphered this within one letter as 'Salve umbistineum geminatum Martia proles': 'Be greeted, double knob, children of Mars.' For the discovery of the phases of Venus, the code 'Haec immatura a me jam frustra leguntur oy' (this was already tried by me in vain too early) hid the message, 'Cynthiae figurae aemulatur mater amorum' (The mother of lovers [Venus] imitates the shapes of Cynthia [the moon]). Despite this exchange, Galileo never accepted Kepler's elliptical orbits.
From 1616, Galileo tried to apply his knowledge of the satellites of Jupiter to the determination of longitude at sea. In order to ensure observation at sea, the Tuscan arsenal made for Galileo a headgear which had a telescope attached. Around this time, he also designed a brass 'Jovilabe', a computing device for prediction positions of the satellites. He hoped to gain support from the Spanish crown for this project, but failed.
