Herschel's forty-foot reflecting telescope, 1795.
© Science Museum / Science & Society Picture Library
Illustration taken from the periodical 'Philosophical Transactions'. This 40-foot telescope was constructed by Sir William Herschel (1738-1822) in the grounds of his home in Slough, and completed in 1789. On the night of 28 August that year, the first time he had used the telescope, Herschel discovered two new moons of the planet Saturn. Herschel was appointed Court Astronomer to George III after discovering the planet Uranus (which he originally named 'The Georgian' in the King's honour) in 1781. In 1820 he published a catalogue of over 5000 nebulae and star clusters observable in the northern hemisphere. Herschel's son John, also an astronomer, compiled a similar catalogue for the southern hemisphere in the 1830s.