The Lake County Astronomical Society

Astronomy Bio...Johannes Hevelius

Jay Bitterman

Johannes Hevelius, (also spelled as Hewel or Hewelcke) was a German astronomer most famous for his careful charting of the surface of the Moon. He was born on January 28, 1611, in Danzig (Gdansk) Northern Poland. 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 17^th century. His wife, Elizabeth, shared his interest and assisted him greatly in the study of the Moon, his catalog of the stars and his work on comets. After his death in 1687, she edited his famous work, Prodromus Astronomiae, and published it in 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 markings in the neighborhood of sunspots. The name he gave to them, faculae, is still used. He also made observations of the planets, particularly Jupiter and Saturn. On November 22, 1644, he observed that Mercury went through phases, which had been predicted by 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 gray regions in 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 Galilei (1564-1642) a generation before. His Selenographia also has an appendix that contains his observations of the Sun from 1642 to 1645.

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 (1546-1601). 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's practice of using only the naked eye to observe positions 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 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.