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All men have stars, but they are not the same things for different people. For some, who are travellers, the stars are guides. For others they are no more than little lights in the sky. For others, who are scholars, they are problems...
- Antoine de Saint-Exupéry, The Little Prince

People throughout history have looked up to the sky for answers: to measure time, mark seasons, and navigate vast oceans. The sky at night inspires with beautiful images, and promises answers to big questions.

The final view is a close-up of the sky around the star cluster Terzan 5 taken with Hubble, the Very Large Telescope at ESO’s Paranal Observatory and the Keck Telescope. Nick Risinger ( Music: Johan B. Monell

Refracting and reflecting

The telescope was probably invented in the Netherlands in 1608, when a spectacle-maker, Hans Lipperhey, put two glass lenses together in a tube, effectively creating a ‘refracting’ telescope. In 1609, Italian scientist Galileo Galilei heard of this optical device and went on to develop ‘refracting’ telescopes with magnifications able to observe the solar system in great detail. But there were drawbacks to the refracting telescope. Despite advancements in optical craftsmanship, image quality was poor due to the nature of the glass. 


Astronomy: 1870s artistic representation of Galileo with his telescope in the Piazza San Marco, Venice. Wood engraving. Wellcome Library, London

In 1663, a Scot, James Gregory (1638-75), published an innovative design for a ‘reflecting’ telescope that used mirrors to form the magnified image, rather than the glass lenses used in the ‘refracting’ telescope. Once various technical problems were overcome, this design resulted in more compact telescopes with sharper images and his design is the predecessor of modern reflecting telescopes.

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    18-inch silvered glass telescope speculum by George With, 1878.

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    Reflecting telescope by Edward Scarlett, London, c. 1730.

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    Reflecting telescope made by James Short of London, c. 1765.

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    Portrait of James Gregory, mathematician and inventor of the reflecting telescope, attributed to Richard Waitt (1708-32).

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    Section of a reflecting telescope for astronomy.

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