Johannes Hevelius

1611-1687

German Astronomer

Johannes Hevelius was the last astronomer of repute to carry out major observational work without a telescope. Though he rejected the use of telescopic sights for stellar observations and positional measurements, he did use telescopes to produce accurate maps of the Moon and is considered the father of lunar topography.

Hevelius was born in Danzig (now Gdansk, Poland) on January 28, 1611. He studied jurisprudence at the University of Leiden before touring Europe. Upon his return he worked in his father's brewery while preparing to enter public service. His occasional interest in astronomy developed into a serious occupation in 1639 when he began making systematic observations. For the rest of his life his time was split between managing the family brewery, civic service, and astronomical research.

Hevelius's first observatory was a small room atop his father's house. In 1644 he added a small roofed tower and later erected a terrace with two observation enclosures to accommodate his large quadrants, sextants, and masts for supporting extremely long telescopes. Hevelius built and used these "aerial" telescopes because his experience and the optical theories of Johannes Kepler (1571-1630) and René Descartes (1596-1650) had shown that strongly curved lenses produced badly distorted images. Weak objective lenses—convex lenses with small curvatures—produced better images but required extremely long telescopes to accommodate the long focal lengths.

Using telescopes of 8.2 to 11.5 feet (2.5 to 3.5 meters) Hevelius observed the phases of Mercury in 1644 that previously had been predicted by Kepler and then observed by Ionnes Zupo in 1639. Hevelius also used these instruments to observe the Moon. These observations provided the material for his Selenographia (1647). The 133 color plates of this work represent the first detailed, accurate maps of the Moon's surface. Many of his names for the Moon's features were taken from Earth's geography and are still used, such as Mare Serenitatis (Pacific Ocean). However, his names for individual craters were not adopted.

Hevelius's next great work was his two-volume Cometographia (1668), in which he discussed the nature of comets and collected a considerable body of literature on comets observed in previous centuries. He considered comets planetary exhalations and believed them responsible for sunspots. Like Giovanni Borelli (1608-1679) he suggested their orbits might be parabolic.

Interested in positional astronomy, Hevelius decided to compile a new star catalog for the Northern Hemisphere, which was to be more extensive and accurate than Tycho Brahe's (1546-1601). In taking positional measurements he preferred naked-eye observations. Some of these measurements appeared in Cometographia, which he sent to certain fellows of the Royal Society, including Robert Hooke (1635-1703). Hooke replied by recommending the use of telescopic sights. Their correspondence continued but Hevelius refused to yield. When the first volume of Machina Coelestis appeared in 1673—it contained much new observational data and a detailed description of Hevelius's observatory and instruments—Hooke publicly criticized him. In 1679 Hooke and John Flamsteed (1646-1719) persuaded Edmond Halley (1656-1742) to pay Hevelius a visit during his tour of Europe and try to convince him of the advantages of the telescope. To Halley's surprise, he found Hevelius could make consistently accurate measurements on par with the best telescopic work.

In September 1679 Hevelius's observatory burned to the ground with most of his instruments and many notes. Though he diligently rebuilt his observatory and constructed new instruments, the loss greatly affected his health. He died on January 28, 1687. His second wife and collaborator, formerly Catherina Elisabeth Koopman, published the Uranographia posthumously in 1690. It is his best known work, cataloging over 1,500 stars and introducing several new constellations, including Lacerta, Leo Minor, Lynx, Scutum, Sextans, and Vulpecula.

STEPHEN D. NORTON