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Summary Article: Hevelius, Johannes (1611-1687)
from The Hutchinson Dictionary of Scientific Biography

Place: Germany

Subject: biography, astronomy

German astronomer, most famous for his careful charting of the surface of the Moon.

Hevelius was born in Danzig (now Gdansk) in northern Poland on 28 January 1611. A wealthy brewing merchant, he had a well-equipped observatory installed on the roof of his house in 1641, and was one of the most active observers of the 17th century. During the daytime he worked in his business and some evenings he took his seat on the city council, but most of the rest of his free time he was up on his roof, observing, noting, and cataloguing. His wife Elizabeth shared his interests and assisted him greatly in the study of the Moon, his catalogue of the stars, and his work on comets. After his death, she edited and published his most famous work, Prodromus astronomiae (1690).

Between 1642 and 1645, Hevelius deduced a fairly accurate value for the period of the solar rotation and gave the first description of the bright ideas in the neighbourhood of sunspots. The name he gave to them, faculae, is still used. He also made observations of the planets, particularly of Jupiter and Saturn. On 22 November 1644 he observed the phases of Mercury, which had been predicted by Nicolaus Copernicus.

In 1647, Hevelius published the first comparatively detailed map of the Moon, based on ten years' observations. It contained diagrams of the different phases for each day of lunation. He realized that the large, uniform grey regions on the lunar disc consisted of low plains, and that the bright contrasting regions represented higher, mountainous relief. He obtained better values for the heights of these lunar mountains than had Galileo a generation before. His Selenographia also has an appendix that contains his observations of the Sun 1642-45.

Hevelius was interested in positional astronomy and planned a new star catalogue of the northern hemisphere, which was to be much more complete than that of Tycho Brahe. He began in 1657, but his observatory, with some of his notes, was destroyed by fire in 1679. Nevertheless, his observations enabled him to catalogue more than 1,500 stellar positions. The resulting Uranographia contains an excellent celestial atlas with 54 plates, but Hevelius' practice of using only the naked eye to observe positions (despite representations by no less a man than Edmond Halley) considerably reduces the value of his work. Hevelius used telescopes for details on the Moon and planets, but refused to apply them to his measuring apparatus.

Hevelius discovered four comets - he called them pseudo-planetae - and suggested that these bodies orbited in parabolic paths about the Sun. Many later writers have declared that this suggestion indicates that he knew the nature of comets earlier than did either Halley or Newton.

A few of the names he gave to features of the Moon's surface are still in use today, particularly those that reflect geographical names on Earth. For his charting of the lunar formations, Hevelius has come to be known as the founder of lunar topography.

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