The 17th-Century Astronomer Who Made the First Atlas of the Moon | Science | Smithsonian Magazine
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The 17th-Century Astronomer Who Made the First Atlas of the Moon
Johannes Hevelius drew some of the first maps of the moon, praised for their detail, from his homemade rooftop observatory in the Kingdom of Poland
In the rare books collection of the Huntington Library in San Marino, California, a large tome tied with string sits in an ivory box that looks like it came from a bakery. At one point, the book belonged to Edwin Hubble, who revealed that galaxies exist beyond our own and that the universe is expanding, among other things, at nearby Mount Wilson Observatory. Between the well-worn leather cover boards, I find some of the first detailed maps of the lunar surface, illustrated and engraved in the 17th century. As I delicately place the volume back in the box, the covers leave a light brown residue on my fingertips—a small remnant of one man’s quest to tame the moon.
The book, titled Selenographia, was created by perhaps the most innovative Polish astronomer since Copernicus. But Johannes Hevelius, as we call him in the English-speaking world, has been somewhat more forgotten among history’s great scientists. Selenographia was the first book of lunar maps and diagrams, extensively covering the moon's various phases. More than 300 years before humans stepped onto the moon’s surface, Hevelius was documenting every crater, slope and valley that he could see with his telescope. He conducted these observations, as well as others for a comprehensive star catalog, using his own equipment in a homemade rooftop observatory.
Published in 1647, Selenographia made Hevelius a celebrity of sorts. The Italian astronomer Niccolo Zucchi even showed a copy of the book to the pope. Of course, like Copernicus before him, Hevelius believed that that the Earth orbited the sun. And according to Johannes Hevelius and His Catalog of Stars, published by Brigham Young University Press, Pope Innocent X said Selenographia "would be a book without parallel, had it not been written by a heretic."
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Hevelius was born in 1611 in Danzig, on the coast of the Baltic Sea in what was then the Kingdom of Poland. Today, the fairytale-like port city is known as Gdańsk. In the Old Town by St. Catherine’s Church, there is a statue of a mustachioed man with a pointy beard gazing at the sky and holding antiquated astronomical tools. The inscription reads, "Jan Heweliusz."
Hevelius’s father expected him to become a businessman in the family trade of brewing, and at age 19 he went to study law at the University of Leiden. He returned to Gdańsk in 1634 and became a merchant, eventually entering public service as a city councilor and then mayor. But Peter Krüger, a teacher who had introduced Hevelius to astronomy, reignited a celestial longing in the young man. On his deathbed, Krüger encouraged Hevelius to devote his life to astronomy—words that sparked an illustrious career.
In 1641, Hevelius constructed an observatory on the rooftops of three adjoining houses that he owned in Gdańsk. Given his significant wealth from the family brewing business, he literally put his beer money toward science. As he both acquired and built elaborate astronomical instruments, this "Star Castle" became one of the greatest observatories in Europe at the time. Esteemed visitors such as Edmond Halley, whose many accomplishments include predicting the return of the comet that bears his name, came to visit and meet with Hevelius, hundreds of miles from other epicenters of astronomy in Paris and London.
Mapping the moon was one of Hevelius’s first major undertakings. The seafaring nations at the time were desperately searching for a way to measure longitude at sea, and it was thought that the moon could provide a solution. The idea was that during a lunar eclipse, if sailors observed the shadow of the moon crossing a particular point on the surface at 3:03 p.m., but they knew that in another location, such as Paris, the same crossing would occur at 3:33 p.m., then they could calculate their degrees of longitude away from the known location of the city. More accurate lunar charts, however, would be required for the technique to be possible (and due to the practical matters of using a large telescope on a rolling ship, a truly reliable way to calculate longitude at sea would not be achieved until the invention of the marine chronometer).
After many long nights on the rooftop peering into his telescopes, Hevelius produced some preliminary drawings and engravings. He sent them to a friend and fellow astronomer based in Paris, Peter Gassendi, who was also interested in mapping the moon. Gassendi was floored by the quality of Hevelius’ work, and he implored him to continue the project.
"You are gifted with such superior eyes, which one could really call the ‘eyes of a Lynx,’" Gassendi wrote, according to Johannes Hevelius and His Catalog of Stars.
Emboldened, this Lynx-eyed astronomer drew the moon every night and then engraved the night’s observations in copper the next morning. At last, after five years, he completed this endeavor with the publication of Selenographia sive Lunae descriptio.
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Hevelius wasn’t the first to use a telescope to draw the moon. Others before him include Thomas Harriot and Galileo Galilei. His maps with named features were published two years after those of Michel Florent van Langren. But Hevelius’s work stands out for its detail and its aesthetics, and his collection of lunar maps are considered the first atlas of the moon.
Selenographia contains some 40 engraved plates showing the moon at different phases. The sketched topography reveals that as more of the moon is illuminated in its cycle, the features visible one night are not in the same location the next. Hevelius also included observations of Saturn, Mars, Jupiter and what he believed were "fixed stars," in addition to descriptions and engravings of astronomical instruments. The book represents the state of the art in telescope astronomy at that time, according to historians Albert Van Helden and Mary G. Winkler.
The work also reflects Hevelius’s keen eye for detail as well as his artistic sensibility. Around the middle of the large book is the first of several crown jewels—engravings of the moon that cover a two-page centerfold-like spread. At the bottom right, an angel peers through a telescope while another jots down notes. On the opposite side of the moon, another pair of angels holds a book and measures angles. Cherubs continue their research in the margins of Selenographia’s largest most impressive lunar maps.
Hevelius named dozens of features across the lunar landscape, but despite the beauty and wonder of his work, most of his names for lunar characteristics have fallen out of favor. Van Helden and R. H. van Gent posit in an essay that Hevelius’s system was just too complicated—he classified features as continents, islands, seas, bays, rocks, swamps, marshes and a host of other categories reflecting Earthly experience. 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. This later work demarcated fewer kinds of features, describing the flat, dark basaltic areas of the moon as "maria," or seas. As fate would have it, Riccioli named Mare Tranquillitatis—the Sea of Tranquillity—where Apollo 11 touched down in 1969.
But Riccioli’s system didn’t begin to take off until the 18th century. Hevelius’s more cumbersome scheme reigned supreme for the rest of his lifetime and then some. And though Riccioli’s system ultimately became the standard, a small contingent of names Hevelius gave to lunar characteristics are still in use today—such as "Alps" for lunar mountains.
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While Hevelius made use of telescopes in his moon mapping efforts, the pioneering astronomer charted the positions of stars without magnification. 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. In this way, he was among the more traditional astronomers of the time.
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. Specifically, an instrument of the day called a sextant, which measured angles between celestial objects or the horizon, had a "sight" or aiming device on each arm. Hooke and Flamsteed argued that using telescopes for sights would make measurements more accurate, while Hevelius disagreed.
History would ultimately prove Hevelius wrong, but nonetheless, his star catalogs were among the most accurate of the time, not surpassed for at least four decades. Hevelius’s final catalog included more than 1,500 entries of stellar positions and magnitudes. In fact, there are researchers today who compare Hevelius’s charts to modern measurements, and according to one analysis, his stellar magnitudes aren’t that far off.
"If Hevelius had spent more time in analyzing his measurements and errors and those of [Danish astronomer] Tycho [Brahe], he might have made the important discovery that the stars are not really fixed but are slowly moving," according to Johannes Hevelius and His Catalog of Stars.
But Johannes Hevelius cannot take all of the credit for this work. His wife Elisabeth holds her own place in the history of astronomy. Born the same year as the publication of Selenographia, Elisabeth Koopman was at least 35 years Hevelius’s junior. Still, this May-December relationship gave Elisabeth the opportunity to work at the forefront of astronomy, and she eagerly embraced the study of the stars with her husband. No one knows exactly where her work began and her husband’s ended, but an engraving shows the two of them operating a sextant together—one would align the instrument with a star while the other focused on another star, so that they could measure the distance between them.
Tragedy struck their painstaking work on September 26, 1679. While Elisabeth and Johannes were away, a coachman "left a burning candle in the stable and set the whole place afire," according to an account reproduced in Johannes Hevelius and His Catalog of Stars.
The astronomical instruments, notes and stacks of manuscripts burned away, and the observatory was largely destroyed. But it is believed that Hevelius’s daughter Katharina had the foresight to save the family’s handwritten Catalogus Stellarum Fixarum (the "Fixed Star Catalog"). Miraculously, this manuscript has managed to escape subsequent blazes and bombings, surviving everything from the 1734 Siege of Danzig to bombings during World War II. As Maria Popova writes for her blog Brainpickings, "This strange phoenix of science finally arrived at Brigham Young University in 1971, where it has remained safe from fire and brimstone in the decades since."
Though Hevelius hoped to publish a complete star catalog, he died in 1687 shortly before accomplishing this goal. His final star catalog was published in 1690 under the direction of his faithful partner in life, science and stargazing, Elisabeth. The work gives names for dozens of constellations that are still used today, including the Lynx—a nod to the miraculously superior eyesight of Jan Heweliusz of Danzig.
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Johannes and Elisabeth Hevelius are buried in the same tomb at St. Catherine’s Church in Gdańsk, where they had been married, near the Hevelius statue. The place where Hevelius lived, dutifully rebuilding his "Star Castle" observatory after the fire, no longer exists. An estimated 90 percent of the city was destroyed in World War II. The "Old Town" of Gdańsk today has been reconstructed to look as it did before 1793, resembling an illustration of the city in one of Hevelius’s books.
As for Selenographia, the Huntington Library near Los Angeles keeps a copy in its history of science exhibit, which also displays influential works by Nicolaus Copernicus, Isaac Newton and others who shaped our view of the universe. Hubble’s copy, with its detached covers that leave a cocoa-powder dusting wherever they are placed, is available on request by scholars, who have been perusing the maps Hevelius left to the world for more than 300 years.
"Hubble’s copy of Selenographia has been put to good use by astronomers over the centuries," Van Helden says, "as Hevelius would have wanted."
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