Astronomical telescope with observer, 1647.
© Science Museum / Science & Society Picture Library
Engraved plate taken from 'Selenographia'(1647) by Johannes Hevelius (1611-1687). Hevelius was an early German astronomer, who established the foremost observatory in Danzig in 1641, and rebuilt it after a fire in 1679. He catalogued 1500 stars, discovered four comets and was one of the first to observe the transit of Mercury. Hevelius also determined the solar rotation period to a much better accuracy than previously achieved, and was said to have had such exceptionally keen eyesight that he could see stars of the seventh magnitude.