Jan Heweliusz (1611 - 1687)

Heweliusz was also an innovator in the construction of observational instruments. He described his equipment in the work Machinae Coelestis (1673). The construction of the telescopes he used for observing the Moon was detailed in the opening chapters of Selenographia (1647).

In Selenographia, he also presented the results of several years of lunar observations in the form of maps and drawings. His lunar map was the most accurate representation of the Moon's surface for the next 100 years. This depiction included the phenomenon of libration, one aspect of which— longitudinal libration—he described for the first time. The book itself became a European bestseller.

Another subject Heweliusz pursued was the observation of comets. He discovered four comets and was the first to hypothesize that comets move along curved paths. In his work Cometographia (1668), he documented 250 comets observed up to 1665 and the results of his own studies.

The culmination of his lifelong observations was the work Prodromus Astronomiae, published posthumously in 1690. It included a catalog of the positions of over 1,500 stars, nearly 600 of which were recorded for the first time by Heweliusz. The treatise also featured a celestial atlas. In it, Heweliusz identified 12 new constellations. The names of some, such as Canes Venatici, Lynx, Sextans Uranii (now Sextans), Sagitta, and Scutum Sobiescianum (now Scutum), are still in use today. The entire work was dedicated to the Polish king, Jan III Sobieski.

The work Selenographia, published in 1647, was Heweliusz's first and one of his greatest scientific achievements. It presented the results of his telescopic observations, primarily concerning the Moon. The lunar maps he published were the most accurate of their time and remained unsurpassed for over 100 years. Heweliusz's maps also accounted for the phenomenon of libration. Although the Moon always faces the Earth with one side, slight oscillations of its disk allow certain points near its edge to become alternately visible and hidden. Due to libration, a total of 59% of the Moon's surface is observable. This phenomenon was discovered by Galileo Galilei (1564–1642), but Heweliusz expanded upon it by identifying an additional component: longitudinal libration. While Heweliusz described the phenomenon, he did not explain its causes. This was later done by Isaac Newton (1643–1727), who based his explanation on Heweliusz's observations. Selenographia also detailed observations of other celestial bodies, including planets, Jupiter's moons, and sunspots.

Heweliusz conducted long-term observations of sunspots, publishing his findings in several works. His observations are especially valuable as they cover a period of reduced solar activity, known as the Maunder Minimum, for which there are currently few observational records. He also introduced the term "faculae," still used today to describe the bright areas around sunspots.

Throughout his life, Heweliusz observed comets. He discovered four and observed seven in total. Some of his findings were presented in his work Cometographia (1668). In this book, Heweliusz became the first astronomer to hypothesize that comets travel along curved paths rather than straight lines, as previously suggested by Johannes Kepler. Definitive proof of this hypothesis was provided several years later by Georg Samuel Dörffel (1643–1688), a Lutheran pastor and amateur astronomer. In his work Astronomical Observation of the Great Comet of 1680–81 (1681), Dörffel demonstrated that the observed comet moved along a parabolic orbit with the Sun at its focus.

On May 3, 1661, a fascinating astronomical phenomenon occurred: the transit of Mercury. This event involved the planet aligning between Earth and the Sun, appearing as a small dot against the solar disk. Observing this phenomenon was possible only through the projection method, in which light passing through a telescope was cast onto a screen. Heweliusz determined the angular diameter of the planet to be 11.8 arcseconds, a measurement remarkably close to the correct value of 13 arcseconds. He described his observations of the transit in the treatise Mercurius in sole visus Gedani, anno christiani 1661.

Heweliusz was the last astronomer of a bygone era in which celestial observations were made with the naked eye. Although he constructed and used telescopes, his extensive work on a star catalog relied on sighting instruments without lenses, such as quadrants, sextants, and octants. These were devices he built himself, characterized by high precision. Using his instruments, positions could be determined with an accuracy of up to 28 arcseconds. After publishing Machinae Coelestis in 1673, which detailed his measurement methods, English scholars criticized him for employing outdated techniques that allegedly introduced errors. As a member of the Royal Society, Heweliusz demanded arbitration. In 1679, the young astronomer Edmond Halley, renowned for his observations of the southern sky, visited Heweliusz. For over a month, the two conducted parallel observations: Heweliusz with his instruments and Halley with telescopes equipped with micrometers. Halley's verdict was favorable to Heweliusz. The English astronomer acknowledged that the accuracy of Heweliusz's measurements was equal to that of his own.

The culmination of many years of positional observations was a three-part work published in 1690, three years after the astronomer's death. The first part, Prodromus Astronomiae, described the methods he employed for taking measurements. Heweliusz provided star positions as of the year 1660, explaining that this marked roughly the midpoint of his observational period. The second part contained a catalog listing the positions of 1,564 stars, of which 950 were known from earlier compilations, while the positions of nearly 600 stars were determined for the first time. The third part, titled Firmamentum Sobiescianum sive Uranographia, was a celestial atlas spread across 56 sheets. In this atlas, Heweliusz introduced several new constellations: Scutum Sobiescianum (Sobieski's Shield), Canes Venatici (Hunting Dogs), Lacerta (Lizard), Leo Minor (Little Lion), Lynx, Sextans Uraniae (Sextant), Sagitta (Arrow), Triangulum Minus (Small Triangle), Antinous, Cerberus, and Mons Maenalis. With the exception of the last four, these constellations are still in use today, though Sobieski's Shield became simply the Shield (Scutum), and Sextans Uraniae is now simply Sextans. The Prodromus was dedicated to Heweliusz’s long-time patron, King John III Sobieski.

Heweliusz was not only an outstanding astronomer but also a skilled constructor of observational instruments. Initially, he used a quadrant funded by the City Council for his mentor, Peter Krüger. Although the instrument remained incomplete, Heweliusz finalized and utilized it in his observatory. He described most of his instruments in the first volume of Machinae Coelestis, accompanied by superb engravings crafted by Isaac Saal, who had been brought from the Netherlands specifically for this purpose. The engravings were based on drawings by Gdańsk painter Andreas Stech (1635–1697). A common feature of the sighting instruments Heweliusz used for positional measurements was a scale inscribed on a segment of a circular arc. The instruments' names derived from the Latin terms for the arc fractions they utilized. Instruments based on one- quarter of a circle (90°) were called quadrants; those using one-sixth (60°) were sextants; and those using one-eighth (45°) were octants. Although the instruments were crafted by Gdańsk artisans, Heweliusz himself carried out the most critical part of the work—engraving the measurement scales.

In his first treatise, Selenographia, Heweliusz described the construction of telescopes he used for his observations. He personally built these telescopes and polished lenses made from Venetian glass. It is worth noting that Selenographia was entirely his own work. Heweliusz constructed the instruments used for observations, wrote the text, created the illustrations, engraved the graphics himself based on these drawings, and ultimately printed the book.

Heweliusz continued building telescopes even after the publication of Selenographia. His most famous instrument was a 46-meter-long telescope, which he used in the fields near the Oliwa Cathedral. This telescope was an example of an aerial telescope, meaning it lacked a fixed tube (as such a structure would have been too heavy to handle) and instead featured an open-frame design. Such large telescopes were constructed to minimize spherical and chromatic aberrations—optical distortions caused by the lenses. For a focusing lens, the greater the radius of curvature of the lens surface, and therefore the longer its focal length, the smaller the image distortions due to these aberrations. However, this telescope was highly inconvenient to operate, which is why Heweliusz used it only sparingly.

Biography

Jan Heweliusz was born on January 28, 1611, in Gdańsk. In 1618, he began his studies at the Academic Gymnasium in Gdańsk, which he continued intermittently until 1630. A significant influence on his later work was his mathematics teacher, Peter Krüger (1580–1639), a former student of Johannes Kepler (1571–1630) and Tycho Brahe (1546–1601). Krüger introduced Heweliusz to astronomy and taught him the construction of measuring instruments.

In 1630, Heweliusz began studying law and economics at Leiden University. However, he was not drawn to law, and the level of astronomy education in Leiden was unsatisfactory. In 1631, he traveled to London, and between 1631 and 1634, he journeyed through France. During this time, he met several distinguished scholars, including Pierre Gassendi (1592–1655), Marin Mersenne (1588–1648), and Athanasius Kircher (1602–1680).

Heweliusz returned to Gdańsk in 1634. Shortly after his return, in 1635, he married Katarzyna Rebeschke (1613–1662), who brought two townhouses neighboring his family home as part of her dowry. Around 1640, Heweliusz began constructing an astronomical observatory on the roofs of his properties.

Heweliusz was born into a family that had been brewing beer for several generations. He continued this family tradition and became a member of the brewers' guild in 1636, later serving as its elder in 1643. In later years, as he devoted more time to scientific pursuits, the management of his breweries fell to his wife. Brewing beer remained their primary source of income. In 1677, King Jan III Sobieski granted him the privilege of the title Nobilis Ioannes Hevelius Astrologus noster Consul Veteris Civitatis Gedanensis and exempted him and his descendants from guild fees. The privilege also allowed him to freely sell beer both within the city and beyond its limits.

In his hometown of Gdańsk, Jan Heweliusz was highly esteemed not only as a scholar but also as a civic leader. He became a city councilor in 1651 and held this position for the rest of his life.

Heweliusz's first wife, Katarzyna, passed away in 1662. A year and a half later, he married Elżbieta Koopman (1647–1693), who actively supported his scientific work. Elżbieta assisted with observations and prepared his scholarly works for publication.

Astronomy was Heweliusz’s greatest passion. As he noted in one of his works, his former teacher Peter Krüger urged him on his deathbed to dedicate himself systematically to astronomy. Heweliusz’s observatory was initially located in the attic of his townhouse on Korzenna Street in Gdańsk. Later, it expanded to include the rooftops of two neighboring houses belonging to his wife. Heweliusz personally crafted most of the instruments used in the observatory, including sighting devices like quadrants and octants, as well as telescopes for which he ground the lenses himself.

In the 1640s, Heweliusz focused primarily on observing the Moon. Using telescopes he built himself, he compiled his findings in the 1647 publication Selenographia sive Lunae descriptio (Selenography, or a Description of the Moon). This work included the most precise lunar map of its time and observations of sunspots and Jupiter's moons.

In 1662, Heweliusz published Mercurius in sole visus Gedani, anno christiani 1661 (Mercury Visible on the Sun in Gdańsk in the Year 1661), documenting the transit of Mercury across the solar disk on May 3, 1661. His 1668 work, Cometographia, provided a comprehensive review of all comets discovered and observed up to 1665, supplemented by his own observations.

Jan Heweliusz’s Machina Coelestis (The Machinery of the Heavens), published in two volumes in 1673 and 1679, detailed the instruments he used and his observational methods. For positional astronomy, which involved determining the positions of stars on the celestial sphere, Heweliusz employed sighting instruments equipped with an alidade—a straightedge with two sights used to target celestial objects. Heweliusz was the last prominent astronomer to rely on such instruments.

English scholars, including royal astronomer John Flamsteed (1646–1719) and physicist Robert Hooke (1635–1703), criticized Heweliusz's methods, questioning the accuracy of his observations due to his use of sighting instruments instead of telescopes equipped with micrometers, which were standard at the Greenwich Observatory. To settle this dispute, the Royal Society sent Edmond Halley (1656–1742) to Gdańsk in May 1679. Halley brought telescopes with measurement devices and conducted comparative observations with Heweliusz. The results demonstrated comparable accuracy, disproving the criticisms of Flamsteed and Hooke.

Heweliusz's observations earned him widespread recognition both in scientific circles and among political leaders. In 1664, he became a foreign member of the English Royal Society. Two years later, in 1666, he was offered the prestigious position of director at the newly established Paris Observatory. However, Heweliusz declined the offer, choosing to remain in Gdańsk.

In 1659, his observatory was visited by King of Poland John II Casimir and Queen Ludwika Maria Gonzaga. The king granted him a privilege allowing Heweliusz to run a printing press and independently print his books. From 1664, for eight years, he received an annual pension from King Louis XIV of France, to whom he dedicated the first volume of Machinae Coelestis as a token of gratitude. The second volume of this work was dedicated to his new patron, King John III Sobieski, whom he had met when Sobieski was still the Crown Marshal. Sobieski visited his observatory and ordered several scientific instruments, including a microscope and two telescopes. When Sobieski, by then king, visited Gdańsk in 1677, he granted him an annual pension of 1000 florins, which was paid to the scholar until his death.

In 1679, a fire destroyed Heweliusz's houses, along with his observatory and instruments, as well as the printing press with nearly the entire print run of Machinae Coelestis Pars Posterior. The 68- year-old scholar began rebuilding his houses and observatory. He received financial aid from his two patrons, John III Sobieski and Louis XIV. Although the reconstruction took several years, by 1680 the astronomer had observed a comet, and from 1682 onward, he conducted systematic observations. The events of that tragic year and the results of subsequent observations were published in 1685 in the volume Annus Climactericus, Sive Rerum Uranicarum Observationum Annus Quadragesimus Nonus (The Climacteric Year...). It also included results of several years of observations of the variable star Mira Ceti.

Heweliusz died on the anniversary of his birth, January 28, 1687. His work was completed by his wife, who, thanks to the continued pension from John III Sobieski, ensured the publication in 1690 of Prodromus Astronomiae Cum Catalogo Fixarum Et Firmamentum Sobiescianum (The Herald of Astronomy ...), consisting of three parts: an introduction, a catalog of 1564 stars, and Firmamentum Sobiescianum Sive Uranographia, an atlas of the heavens.