<p>The <i>Sidereus nuncius</i>, a title commonly translated as the <i>Starry messenger</i>, is a book printed and published within a few months of the date of the observations it reported. The stimulus to Galileo’s new observations and the haste to publish an illustrated book was the discovery made in about 1608 by opticians in the Low Countries that two lenses placed at the correct distance when their optical axes were in line gave a magnified image of distant objects, the founding principle of the telescope. A tube of card or wood between the lenses held them in line and cut out extraneous light. Some months after the discovery was in early 1609 in Venice, where he heard of the new instrument and so he constructed one himself. Whereas the first use of the telescope seems to have been for terrestrial observations it occurred to Galileo that the telescope could be raised to the heavens to bring celestial objects apparently closer to the observer. Galileo’s first telescope gave a magnification of about 3 times with a somewhat distorted image but this he soon increased 10-fold – it was a huge leap in our observational capabilities.</p> <p>The <i>Messenger</i> brought news of little succour to Church dogma. Galileo looked at the Sun (something never to be tried at home), at the stars, Moon and planets. The Moon, situated above the imperfect Earth, was far from the perfect white sphere assume but apparently pock-marked by impact and with mountainous regions like Earth’s. There were spots upon the Sun, even, albeit the source of light and warmth; though the stars themselves seemed brighter there was no change in their aspect but the fine dusting of background light he found to be made up of tiny stars forming the Milky Way, our own galaxy we now realise, and there was in patches irregular nebulosity, for instance around Orion’s belt. The planets showed tiny discs while the stars remained points, Saturn had bulges around it and Venus had a crescent phase much as the Moon did. From the viewpoint of dogma perhaps most damaging of all was his discovery of the four moons orbiting Jupiter. Galileo named these the four Medicean stars after the family of his patrons. Galileo had shown empirically that there were bodies that orbited other planets and that this was not exclusively the Earth’s prerogative.</p> <p>What Galileo could not show empirically was that the Earth moved around the Sun; three centuries of technical development would be needed before that was demonstrated. Nonetheless Galileo took this as a self-evident and this caused him to cross swords with one of Bruno’s Inquisitors, Cardinal Bellarmine, who had in 1616 explicitly stated the Church’s rejections of Coperincanism. Bellarmine died in 1621 but the Church held the power of life and death and Galileo’s assertion brought him before the Inquisition in Rome in 1633. This was the same body that had sealed the grim fate of Giordano little more than three decades before, in the light of which it seems of small wonder that Galileo submitted to the Inquisitors and wrote his recantation of his resolute conviction.</p> <p>Adam Perkins, Curator of Scientific Manuscripts</p> <p>This item is included in the Library’s 600th anniversary exhibition <a href="https://exhibitions.lib.cam.ac.uk/linesofthought/artifacts/seeing-the-stars/"><i>Lines of Thought: Discoveries that changed the world</i></a> which runs until 30 September 2016.</p>
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