German astronomer Johannes Hevelius is often regarded as one of the last great astronomers to carry out major observational work without a telescope. With the aid of only a quadrant and an alidade, Hevelius compiled a catalog of more than fifteen hundred stars with unprecedented accuracy. It was the most comprehensive celestial atlas of its time. However, it was through the use of telescopes that Hevelius gained fame as “the founder of lunar topography”. He produced the first detailed map of the moon documenting every crater, slope and valley that he could see with his telescope.
The surface of the Moon by Johannes Hevelius.
Johannes Hevelius was born in 1611 in Danzig, Poland. His father owned a profitable brewery and wanted his son to become a businessman like himself. At the age of 19, Hevelius went to study law at the University of Leiden. He returned to Gdańsk in 1634 and became a brewer himself, but his mathematics teacher, Peter Krüger, managed to inspire young Hevelius in astronomy.
In 1641, Hevelius constructed an observatory on the rooftops of three adjoining houses that he owned in Gdańsk. He filled this observatory with splendid instruments, ultimately including a large Keplerian telescope of 150 feet focal length. The observatory was known by the name Sternenburg or “Star Castle”, and it became one of the greatest observatories in Europe at the time. His observatory was visited by many dignitaries, such as the Polish King John III Sobieski and English astronomer Edmond Halley.
Johannes Hevelius
One of Hevelius’s first major undertakings was mapping of the moon. Peering through the telescope trained towards the natural satellite, Hevelius spent countless nights producing drawings of the moon’s surface, just like Galileo had four decades earlier, only Hevelius’s quality of work far surpassed that of the Italian astronomer. When Hevelius sent his drawings to Peter Gassendi, a friend and fellow astronomer based in Paris, Gassendi was so impressed by Hevelius’s work that he implored his friend to continue the project.
“You are gifted with such superior eyes, which one could really call the ‘eyes of a Lynx,’” Gassendi wrote.
Hevelius continued mapping the moon, producing copper engravings of every sketch he made. At the end of five years, he had produced some 40 engraved plates. Together they represents the first detailed, accurate maps of the moon's surface. Hevelius published them under the name Selenographia.
Hevelius's 150 feet focal-length telescope.
Hevelius also named dozens of features across the lunar landscape. However, most of his names for lunar characteristics have fallen out of favor because his names were based on Earth's geography. Thus, there were continents, islands, seas, bays, rocks, swamps, marshes and so on. Such names were replaced largely by the efforts of Giambattista Riccioli and Francesco Maria Grimaldi who collaborated on topographical maps of the moon published in 1651. Nonetheless, a small number of names Hevelius gave to lunar characteristics are still in use today—such as “Alps” for lunar mountains.
While Hevelius made use of telescopes to map the moon, the astronomer charted the positions of stars without using one. To Hevelius, telescopes were for making discoveries, not measurements, says historian Albert Van Helden, professor emeritus at Rice University in Texas and Utrecht University in the Netherlands.
Hevelius and second wife Elisabeth observing the sky with a brass sextant.
Hevelius’s strong feelings about naked-eye astronomy led to a famous debate with famed English polymath Robert Hooke and the first Astronomer Royal, John Flamsteed. Hooke recommended the use of telescopic sights in sextants, which measured angles between celestial objects and the horizon, arguing that using magnification makes measurement more accurate. Hevelius refused and in 1673 produced his first star catalogue, which, despite being mapped without the aid of telescope, was among the most accurate of the time, not surpassed for at least four decades.
In 1679, a tragic fire in his home and observatory destroyed all his instruments and books. Hevelius’s daughter Katharina, however, managed to rescue the manuscript of Catalogus Stellarum Fixarum (the “Fixed Star Catalog”). This manuscript is currently at Brigham Young University.
Johannes Hevelius died in 1687.
References:
# Elizabeth Landau, “The 17th-Century Astronomer Who Made the First Atlas of the Moon”, Smithsonian Magazine
# “Johannes Hevelius”, Mac Tutor
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