Giovanni Battista Riccioli

Giovanni Battista Riccioli

Giovanni Battista Riccioli (17 April 1598 – 25 June 1671; also "Giambattista" and "Giovambatista") was an Italian
Italy , officially the Italian Republic languages]] under the European Charter for Regional or Minority Languages. In each of these, Italy's official name is as follows:;;;;;;;;), is a unitary parliamentary republic in South-Central Europe. To the north it borders France, Switzerland, Austria and...

An astronomer is a scientist who studies celestial bodies such as planets, stars and galaxies.Historically, astronomy was more concerned with the classification and description of phenomena in the sky, while astrophysics attempted to explain these phenomena and the differences between them using...

 and a Catholic priest
A priest is a person authorized to perform the sacred rites of a religion, especially as a mediatory agent between humans and deities. They also have the authority or power to administer religious rites; in particular, rites of sacrifice to, and propitiation of, a deity or deities...

 in the Jesuit (Society of Jesus) order. He is known for his experiments with pendulums and with falling bodies such as lead and wooden balls, for his work concerning the moon, and for his discussion of 126 arguments concerning the motion of the Earth, among other things.

Riccioli was born in Ferrara
Ferrara is a city and comune in Emilia-Romagna, northern Italy, capital city of the Province of Ferrara. It is situated 50 km north-northeast of Bologna, on the Po di Volano, a branch channel of the main stream of the Po River, located 5 km north...

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Giovanni Battista Riccioli (17 April 1598 – 25 June 1671; also "Giambattista" and "Giovambatista") was an Italian
Italy , officially the Italian Republic languages]] under the European Charter for Regional or Minority Languages. In each of these, Italy's official name is as follows:;;;;;;;;), is a unitary parliamentary republic in South-Central Europe. To the north it borders France, Switzerland, Austria and...

An astronomer is a scientist who studies celestial bodies such as planets, stars and galaxies.Historically, astronomy was more concerned with the classification and description of phenomena in the sky, while astrophysics attempted to explain these phenomena and the differences between them using...

 and a Catholic priest
A priest is a person authorized to perform the sacred rites of a religion, especially as a mediatory agent between humans and deities. They also have the authority or power to administer religious rites; in particular, rites of sacrifice to, and propitiation of, a deity or deities...

 in the Jesuit (Society of Jesus) order. He is known for his experiments with pendulums and with falling bodies such as lead and wooden balls, for his work concerning the moon, and for his discussion of 126 arguments concerning the motion of the Earth, among other things.


Riccioli was born in Ferrara
Ferrara is a city and comune in Emilia-Romagna, northern Italy, capital city of the Province of Ferrara. It is situated 50 km north-northeast of Bologna, on the Po di Volano, a branch channel of the main stream of the Po River, located 5 km north...

. He entered the Society of Jesus on 6 October 1614. After completing his novitiate, he began study of the humanities in 1616, pursuing those studies first at Ferrara, and then at Piacenza
Piacenza is a city and comune in the Emilia-Romagna region of northern Italy. It is the capital of the province of Piacenza...


From 1620 to 1628 he studied philosophy and theology at the College of Parma
Parma is a city in the Italian region of Emilia-Romagna famous for its ham, its cheese, its architecture and the fine countryside around it. This is the home of the University of Parma, one of the oldest universities in the world....

. Parma Jesuits had developed a strong program of experimentation, such as with falling bodies. One of the most famous Italian Jesuits of the time, Giuseppe Biancani
Giuseppe Biancani
Giuseppe Biancani was an Italian Jesuit astronomer, mathematician, and selenographer, after whom the crater Blancanus on the Moon is named...

 (1565–1624), was teaching at Parma when Riccioli arrived there. Riccioli mentions Biancani, who accepted new astronomical ideas such as the existence of lunar mountains and the fluid nature of the heavens, and who collaborated with the Jesuit astronomer Christoph Scheiner
Christoph Scheiner
Christoph Scheiner SJ was a Jesuit priest, physicist and astronomer in Ingolstadt....

 (1573–1650) on sunspot observations, with gratitude and admiration.

By 1628 Riccioli's studies were complete. He was ordained. He requested missionary work, but that request was turned down. Instead he was assigned to teach at Parma. There he taught logic, physics, and metaphysics from 1629 to 1632, and engaged in some experiments with falling bodies and pendula. In 1632 he became a member of a group charged with the formation of younger Jesuits. He spent the 1633-1634 academic year in Mantua
Mantua is a city and comune in Lombardy, Italy and capital of the province of the same name. Mantua's historic power and influence under the Gonzaga family, made it one of the main artistic, cultural and notably musical hubs of Northern Italy and the country as a whole...

, where he collaborated with Niccolo Cabeo
Niccolo Cabeo
Niccolò Cabeo was an Italian Jesuit philosopher, theologian, engineer and mathematician.-Biography:He was born in Ferrara in 1586, and was educated at the Jesuit college in Parma beginning in 1602...

 (1576–1650) in further pendulum studies. In 1635 he was back at Parma, where he taught theology and also carried out his first important observation of the moon. In 1636 he was sent to Bologna
Bologna is the capital city of Emilia-Romagna, in the Po Valley of Northern Italy. The city lies between the Po River and the Apennine Mountains, more specifically, between the Reno River and the Savena River. Bologna is a lively and cosmopolitan Italian college city, with spectacular history,...

 to serve as Professor of theology.

Riccioli described himself as a theologian, but one with a strong and ongoing interest in astronomy since since his student days, when he studied under Biancani. He said that many Jesuits were theologians, but few were astronomers. He said that once the enthusiasm for astronomy arose within him he could never extinguish it, and so he became more committed to astronomy than theology. Eventually his superiors in the Jesuit order officially assigned him to the task of astronomical research. However, he also continued to write on theology (see Selected Works, below).

Riccioli built an astronomical observatory in Bologna at the College of St. Lucia, equipped with many instruments for astronomical observations, including telescopes, quadrants, sextants, and other traditional instruments. Riccioli dealt not only with astronomy in his research, but also with physics, arithmetic, geometry, optics, gnomonics, geography, and chronology. He collaborated with others in his work, including other Jesuits, most notably Francesco Maria Grimaldi
Francesco Maria Grimaldi
Francesco Maria Grimaldi was an Italian Jesuit priest, mathematician and physicist who taught at the Jesuit college in Bologna....

 (1618–1663) at Bolgna, and he kept up a voluminous correspondence with others who shared his interests, including Hevelius, Huygens, Cassini, and Kircher. Louis XIV
Louis XIV of France
Louis XIV , known as Louis the Great or the Sun King , was a Bourbon monarch who ruled as King of France and Navarre. His reign, from 1643 to his death in 1715, began at the age of four and lasted seventy-two years, three months, and eighteen days...

 awarded Riccioli a prize in recognition of all his activities and their relevance to contemporary culture.

Riccioli died in Bologna at 73 years of age. He continued to publish on both astronomy and theology up to his death.

The Almagestum Novum (New Almagest)

One of Riccioli's most significant works was his 1651 Almagestum Novum (New Almagest
The Almagest is a 2nd-century mathematical and astronomical treatise on the apparent motions of the stars and planetary paths. Written in Greek by Claudius Ptolemy, a Roman era scholar of Egypt,...

), an encyclopedic work consisting of over 1500 folio pages (38 cm x 25 cm) densely packed with text, tables, and illustrations. It became a standard technical reference book for astronomers all over Europe, “a text no serious seventeenth century astronomer could do without”; John Flamsteed
John Flamsteed
Sir John Flamsteed FRS was an English astronomer and the first Astronomer Royal. He catalogued over 3000 stars.- Life :Flamsteed was born in Denby, Derbyshire, England, the only son of Stephen Flamsteed...

 (1646–1719), the first English astronomer royal, a Copernican and a Protestant, used it for his Grehsam lectures; Jérôme Lalande
Jérôme Lalande
Joseph Jérôme Lefrançois de Lalande was a French astronomer and writer.-Biography:Lalande was born at Bourg-en-Bresse...

 (1732–1807) of the Paris Observatory
Paris Observatory
The Paris Observatory is the foremost astronomical observatory of France, and one of the largest astronomical centres in the world...

 cited it extensively even though it was an old book at that point; the old Catholic Encyclopedia calls it the most important literary work of the Jesuits during the seventeenth century. Within its two volumes were ten “books” covering every subject within astronomy and related to astronomy at the time. Book 1 discusses the celestial sphere and subjects such as celestial motions, the equator, ecliptic, zodiac, etc.; Book 2 the earth and its size, gravity and pendulum motion, etc.; Book 3 the sun, its size and distance, its motion, observations involving it, etc.; Book 4 the moon, its phases, its size and distance, etc. (detailed maps of the moon as seen through a telescope were included); Book 5 lunar and solar eclipses; Book 6 the fixed stars; Book 7 the planets and their motions, etc. (representations of each as seen with a telescope were included); Book 8 comets and novae (“new stars”); Book 9 the structure of the universe — the heliocentric and geocentric theories, etc.; Book 10 calculations related to astronomy. Riccioli envisioned that the New Almagest would have three volumes, but only the first (with its 1500 pages split into two parts) was completed.

Pendulums and Falling Bodies

Riccioli is credited with being the first person to measure the acceleration due to gravity of falling bodies. Within Books 2 and 9 of the New Almagest Riccioli included a significant discussion of and extensive experimental reports on the motions of falling bodies and pendulums.

He was interested in the pendulum as a device for precisely measuring time. By counting the number of pendulum swings that elapsed between transits of certain stars, Riccioli was able to experimentally verify that the period of a pendulum swinging with small amplitude is constant to within two swings out of 3212 (0.062%). He also reported that a pendulum's period increases if the amplitude of its swing is increased to 40 degrees. He sought to develop a pendulum whose period was precisely one second – such a pendulum would complete 86,400 swings in a 24 hour period. This he directly tested, twice, by using stars to mark time and recruiting a team of nine fellow Jesuits to count swings and maintain the amplitude of swing for 24 hours. The results were pendulums with periods within 1.85%, and then 0.69%, of the desired value; and Riccioli even sought to improve on the latter value. The seconds pendulum was then used as a standard for calibrating pendulums with different periods. Riccioli said that for measuring time a pendulum was not a perfectly reliable tool, but in comparison with other methods it was an exceedingly reliable tool.

With pendulums to keep time (sometimes augmented by a chorus of Jesuits chanting in time with a pendulum to provide an audible timer) and a tall structure in the form of Bologna's Torre de Asinelli
Towers of Bologna
The Towers of Bologna are a group of medieval structures in Bologna, Italy. The two most prominent ones, also called the Two Towers, are the landmark of the city.-History:...

 from which to drop objects, Riccioli was able to engage in precise experiments with falling bodies. He verified that falling bodies followed Galileo's “odd-number” rule so that the distance travelled by a falling body increases in proportion to the square of the time of fall, indicative of constant acceleration. According to Riccioli, a falling body released from rest travels 15 Roman feet (29.57 cm) in one second, 60 feet in two seconds, 135 feet in three seconds, etc. Other Jesuits such as the above-mentioned Cabeo had argued that this rule had not been rigorously demonstrated. His results showed that, while falling bodies generally showed constant acceleration, there were differences determined by weight and size and density. Riccioli said that if two heavy objects of differing weight are dropped simultaneously from the same height, the heavier one descends more quickly so long as it is of equal or greater density; if both objects are of equal weight the denser one descends more quickly.

For example, in dropping balls of wood and lead that both weighed 2.5 ounces, Riccioli found that upon the leaden ball having traversed 280 Roman feet the wooden ball had traversed only 240 feet (a table in the New Almagest contains data on twenty one such paired drops). He attributed such differences to the air, and noted that air density had to be considered when dealing with falling bodies. He illustrated the reliability of his experiments by providing detailed descriptions of how they were carried out, so that anyone could reproduce them, complete with diagrams of the Torre de Asinelli that showed heights, drop locations, etc.

Riccioli noted that while these differences did contradict Galileo's claim that balls of differing weight would fall at the same rate, it was possible Galileo observed the fall of bodies made of the same material but of differing sizes, for in that case the difference in fall time between the two balls is much smaller than if the balls are of same size but differing materials, or of the same weight but differing sizes, etc., and that difference is not apparent unless the balls are released from a very great height. At the time, various people had expressed concern with Galileo's ideas about falling bodies, arguing that it would be impossible to discern the small differences in time and distance needed to adequately test Galileo's ideas, or reporting that experiments had not agreed with Galileo's predictions, or complaining that suitably tall buildings with clear paths of fall were not available to thoroughly test Galileo's ideas. By contrast, Riccioli was able to show that he had carried out repeated, consistent, precise experiments in an ideal location. Thus as D. B. Meli notes,

Riccioli's accurate experiments were widely known during the second half of the [seventeenth] century and helped forge a consensus on the empirical adequacy of some aspects of Galileo's work, especially the odd-number rule and the notion that heavy bodies fall with similar accelerations and speed is not proportional to weight. His limited agreement with Galileo was significant, coming as it did from an unsympathetic reader who had gone so far as to include the text of Galileo's condemnation in his own publications.

Working Concerning the Moon

Riccioli and Grimaldi extensively studied the moon, of which Grimaldi drew maps. This material was included in Book 4 of the New Almagest. Grimaldi's maps were based on earlier work by Johannes Hevelius and Michael Van Langren. On one of these maps, Riccioli provided names for lunar features — names which are the basis for the nomenclature of lunar features still in use today. For example, Mare Tranquillitatis
Mare Tranquillitatis
Mare Tranquillitatis is a lunar mare that sits within the Tranquillitatis basin on the Moon. The mare material within the basin consists of basalt formed in the intermediate to young age group of the Upper Imbrian epoch. The surrounding mountains are thought to be of the Lower Imbrian epoch, but...

 (The Sea of Tranquility, site of the Apollo 11 landing in 1969), received its name from Riccioli. Riccioli named large lunar areas for weather. He named craters for significant astronomers, grouping them by philosophies and time periods. Although Riccioli rejected the Copernican theory, he named a prominent lunar crater “Copernicus”
Copernicus (lunar crater)
Copernicus is a prominent lunar impact crater named after the astronomer Nicolaus Copernicus, located in eastern Oceanus Procellarum. It is estimated to be about 800 million years old, and typifies craters that formed during the Copernican period in that it has a prominent ray system.-...

, and he named other important craters after other proponents of the Copernican theory such as Kepler
Johannes Kepler
Johannes Kepler was a German mathematician, astronomer and astrologer. A key figure in the 17th century scientific revolution, he is best known for his eponymous laws of planetary motion, codified by later astronomers, based on his works Astronomia nova, Harmonices Mundi, and Epitome of Copernican...

, Galileo
Galileo Galilei
Galileo Galilei , was an Italian physicist, mathematician, astronomer, and philosopher who played a major role in the Scientific Revolution. His achievements include improvements to the telescope and consequent astronomical observations and support for Copernicanism...

 and Lansbergius. Because craters that he and Grimaldi named after themselves are in the same general vicinity as these, while craters named for some other Jesuit astronomers are in a different part of the Moon, near the very prominent crater named for Tycho
Tycho (crater)
Tycho is a prominent lunar impact crater located in the southern lunar highlands, named after the Danish astronomer Tycho Brahe . To the south is the crater Street; to the east is Pictet, and to the north-northeast is Sasserides. The surface around Tycho is replete with craters of various sizes,...

 Brahe, Riccioli's lunar nomenclature has at times been considered to be a tacit expression of sympathy for a Copernican theory that, as a Jesuit, he could not publicly support. However, Riccioli said he put the Copernicans all in stormy waters (the Oceanus Procellarum). Another noteworthy feature of the map is that Riccioli included on it a direct statement that the moon is not inhabited. This ran counter to speculations about an inhabited moon that had been present in the works of Nicholas of Cusa, Giordano Bruno, and even Kepler, and which would continue on in works of later writers such as Bernard Fontenelle and William Herschel.

Arguments Concerning the Motion of the Earth

A substantial portion of the New Almagest (Book 9, consisting of 343 pages) is devoted to an analysis of the world system question: Is the universe geocentric or heliocentric? Does the Earth move or is it immobile? The historian of science Edward Grant has described Book 9 as being the “lengthiest, most penetrating, and authoritative” analysis of this question made by “any author of the sixteenth and seventeenth centuries”, apparently superseding even Galileo's Dialogue Concerning the Two Chief World Systems – Ptolemaic and Copernican in his opinion, and indeed one writer has recently described Book 9 as “the book Galileo was supposed to write”. Within Book 9 Riccioli discusses 126 arguments concerning Earth's motion – 49 for and 77 against. As the frontispiece of the New Almagest clearly illustrates (see figure at right), to Riccioli the question was not between the geocentric world system of Ptolemy and the heliocentric world system of Copernicus, for the telescope had unseated the Ptolemaic system; it was between the geocentric world system developed by Tycho Brahe in the 1570s (in which the sun, moon, and stars circle an immobile Earth, while the planets circle the sun – sometimes called a “geo-heliocentric” or “hybrid” system) and that of Copernicus.

Many writers make references to Riccioli's analysis and the 126 arguments. However, translations of arguments from the Latin of the New Almagest into more modern languages, and discussions of the arguments to any extent by more modern writers are rare: Only for three arguments of the 126 are such translations and discussions readily available. These are, first, an argument Riccioli called the “physico-mathematical argument” which was related to one of Galileo's conjectures; second, an argument based on what today is known as the “Coriolis effect”; third, an argument based on the appearance of stars as seen through the telescopes of the time.
The “Physico-Mathematical” Argument

Riccioli discusses the physico-mathematical argument in terms of arguments both for and against Earth's motion. Galileo offered a conjecture in his 1632 Dialogue that the apparent linear acceleration of a stone falling from a tower was the result of two uniform circular motions acting in combination – the daily rotation of Earth, and a second uniform circular motion belonging to the stone and acquired from being carried along by the tower. Galileo says that
[T]he true and real motion of the stone is never accelerated at all, but is always equable and uniform.... So we need not look for any other causes of acceleration or any other motions, for the moving body, whether remaining on the tower or falling, moves always in the same manner; that is, circularly, with the same rapidity, and with the same uniformity.... if the line described by a falling body is not exactly this, it is very near to it... [and] according to these considerations, straight motion goes entirely out the window and nature never makes any use of it at all.
Riccioli explained that this conjecture could not work: It could not apply to the fall of bodies near the Earth's poles, where there would be little or no circular motion caused by Earth's rotation; and even at the equator where there would be more motion caused by Earth's rotation, the rate of fall predicted by Galileo's idea was too slow. Riccioli argued that the problems with Galileo's conjecture were a mark against the Copernican world system, but modern writers differ in regards to Riccioli's reasoning on this.
The “Coriolis Effect” Argument

Riccioli also argued that the rotation of the Earth should reveal itself in the flight of artillery projectiles, because on a rotating Earth the ground moves at different speeds at different latitudes. He wrote that
If a ball is fired along a Meridian toward the pole (rather than toward the East or West), diurnal motion will cause the ball to be carried off [that is, the trajectory of the ball will be deflected], all things being equal: for on parallels of latitude nearer the poles, the ground moves more slowly, whereas on parallels nearer the equator, the ground moves more rapidly.
Therefore, were a cannon, aimed directly at a target to the north, to fire a ball, that ball would strike slightly to the east (right) of the target, thanks to the Earth’s rotation. But, if the cannon were fired to the east there would be no deflection, as both cannon and target would move the same distance in the same direction. Riccioli said that the best of cannoneers could fire a ball right into the mouth of an enemy’s cannon; if this deflection effect existed in northward shots they would have detected it. Riccioli argued that the absence of this effect indicated that the Earth does not rotate. He was correct in his reasoning in that the effect he describes actually does occur. It is known today as the Coriolis effect
Coriolis effect
In physics, the Coriolis effect is a deflection of moving objects when they are viewed in a rotating reference frame. In a reference frame with clockwise rotation, the deflection is to the left of the motion of the object; in one with counter-clockwise rotation, the deflection is to the right...

 after the nineteenth-century physicist Gaspard-Gustave Coriolis
Gaspard-Gustave Coriolis
Gaspard-Gustave de Coriolis or Gustave Coriolis was a French mathematician, mechanical engineer and scientist. He is best known for his work on the supplementary forces that are detected in a rotating frame of reference. See the Coriolis Effect...

 (1792–1843). However, the rightward deflection actually occurs regardless of the direction the cannon is pointed (a much more developed understanding of physics than what was available in Riccioli's time is required to explain this), and so cannoneers would not notice any differences based on direction.
The Star Size Argument

Riccioli also used telescopic observations of stars to argue against the Copernican theory. Viewed through the small telescopes of his time, stars appeared as small but distinct disks. These disks were spurious – caused by the diffraction of waves of light entering the telescope. Today they are known as Airy disks, after the nineteenth-century astronomer George Biddell Airy
George Biddell Airy
Sir George Biddell Airy PRS KCB was an English mathematician and astronomer, Astronomer Royal from 1835 to 1881...

 (1801–1892). The real disks of stars are generally too tiny to be seen even with the best of modern telescopes. But during most of the seventeenth century it was thought that these disks seen in a telescope were the actual bodies of stars. In the Copernican theory, the stars had to lie at vast distances from Earth in order to explain why no annual parallax was seen among them. Riccioli and Grimaldi made numerous measurements of star disks using a telescope, providing a detailed description of their procedure so that anyone who wanted could replicate it. Riccioli then calculated the physical size that the stars they measured must have in order for them to both be as far away as was required in the Copernican theory to show no parallax, and have the sizes seen with the telescope. The result in all cases was that the stars were huge – dwarfing the sun. In some scenarios one single star would exceed the size of the entire universe as estimated by a geocentrist like Tycho Brahe. This problem that the appearance of stars in the telescope posed for the Copernican theory had been noted as early as 1614 by Simon Marius, who said telescopic observations of the disks of stars supported the Tychonic theory. The problem was acknowledged by Copernicans such as Martin van den Hove
Martin van den Hove
Martin van den Hove was a Dutch astronomer and mathematician. His adopted Latin name is a translation of the Dutch hof , in Latin horta.-Early life:...

 (1605–1639), who also measured the disks of stars and acknowledged that the issue of vast star sizes might lead people to reject the Copernican theory.
Other Arguments

The other arguments Riccioli presents in Book 9 of the New Almagest were diverse. There were arguments concerning: whether buildings could stand or birds could fly if Earth rotated; what sorts of motions were natural to heavy objects; what constitutes the more simple and elegant celestial arrangement; whether the heavens or the Earth was the more suited for motion and the more easily and economically moved; whether the center of the universe was a more or less noble position; and many others. Many of the anti-Copernican arguments in the New Almagest had roots in the anti-Copernican arguments of Tycho Brahe.

Riccioli argued vigorously against the Copernican system, and even characterized certain arguments for terrestrial immobility as unanswerable, but he also also rebutted some anti-Copernican arguments, invoking counterarguments from the Copernicans. For example, he presents the common opinion that, if the Earth rotated, we ought to feel it, and since we do not, the Earth must be immobile. But he then says that mathematically there is no necessity for such a sensation. He likewise dismisses the ideas that buildings might be ruined or birds left behind by Earth's motion – all may simply share the eastward rotational motion of Earth, like the east-facing cannon and ball discussed above. Perhaps for this reason Riccioli has at times been portrayed as a secret Copernican – someone whose position as a Jesuit necessitated opposition to the Copernican theory.

The Astronomia Reformata (Reformed Astronomy)

Another prominent astronomical publication of Riccioli's was his 1665 Astronomia Reformata (Reformed Astronomy) – another large volume, although only half the length of the New Almagest. The contents of the two significantly overlap; the Reformed Astronomy might be thought of as a condensed and updated version of the New Almagest.
The Reformed Astronomy contains an extensive report on the changing appearance of Saturn. Included in the section on Jupiter is an apparent record of a very early (if not the earliest) observation of Jupiter's Great Red Spot, made by Leander Bandtius, Abbot of Dunisburgh and owner of a particularly fine telescope, in late 1632. Also in that section Riccioli includes reports of Jovian cloud belts appearing and disappearing over time.

The appearance of the physico-mathematical argument in the Reformed Astronomy was the occasion for Stefano degli Angeli (1623-1679?) to launch an “unexpected, somewhat disrespectful and sometimes flippant attack” on Riccioli and the argument. James Gregory published a report in England in 1668 on the resulting public and personal dispute on the matter of falling objects. This was a prelude to Robert Hooke's (1635–1703) invitation to Isaac Newton
Isaac Newton
Sir Isaac Newton PRS was an English physicist, mathematician, astronomer, natural philosopher, alchemist, and theologian, who has been "considered by many to be the greatest and most influential scientist who ever lived."...

 (1642–1727) to resume his scientific correspondence with the Royal Society, and to their ensuing discussion about the trajectory of falling bodies “that turned Newton's mind away from 'other business' and back to the study of terrestrial and celestial mechanics.”
The Reformed Astronomy featured an adaptation to the accumulating observational evidence in favor of Johannes Kepler's elliptical celestial mechanics: It incorporated elliptical orbits into the geo-heliocentric Tychonic theory. Riccioli accepted Kepler's ideas, but remained opposed to the heliocentric theory. Indeed, following the dispute with Angeli, Riccioli's attitude toward heliocentrism hardened.

Other Work

Between 1644 and 1656, Riccioli was occupied by topographical measurements, working with Grimaldi, determining values for the circumference of Earth and the ratio of water to land. Defects of method, however, gave a less accurate value for degrees of arc of the meridian than Snellius
Snellius may refer to:*Rudolph Snellius , a Dutch linguist and mathematician at the Universities of Marburg and Leiden*Snellius , a lunar crater located near the southeast limb of the Moon...

 had achieved a few years earlier. Snellius had been mistaken by approximately 4,000 meters; but Riccioli was more than 10,000 meters in error. Riccioli had come up with 373,000 pes
Pes (length)
A pes is an ancient Roman unit of length that roughly corresponds to a foot. There are twelve unciae in one pes. One pes is 11.6 inches or 29.5 centimeters. There are 2.5 pedes in one gradus....

 despite the fact that references to a Roman degree in antiquity had always been 75 milliare or 375,000 pes. He is often credited with being one of the first to telescopically observe the star Mizar
Mizar (star)
The Mizar–Alcor stellar sextuple system consists of the quadruple system Mizar and the binary system Alcor.- Description :Mizar is a quadruple system of two binary stars in the constellation Ursa Major and is the second star from the end of the Big Dipper's handle. Its apparent magnitude is 2.23...

 and note that it was a double star
Double star
In observational astronomy, a double star is a pair of stars that appear close to each other in the sky as seen from Earth when viewed through an optical telescope. This can happen either because the pair forms a binary star, i.e...

; however, Galileo observed it much earlier.

In the words of Alfredo Dinis,
Riccioli enjoyed great prestige and great opposition, both in Italy and abroad, not only as a man of encyclopedic knowledge but also as someone who could understand and discuss all the relevant issues in cosmology, observational astronomy, and geography of the time.



  • Evangelium unicum Domini nostri Jesu Christi ex verbis ipsis quatuor Evangelistarum conflatum ... (1667)
  • Immunitas ab errore tam speculativo quam practico definitionum S. Sedis Apostolicae in canonizatione Sanctorum ... (1668)
  • De distinctionibus entium in Deo et in creaturis tractatus philosophicus ac theologicus (1669)

See also

  • List of Jesuit scientists
  • List of Roman Catholic scientist-clerics
  • Riccioli (crater)
    Riccioli (crater)
    Riccioli is a large lunar impact crater located near the western limb of the Moon. It lies just to the northwest of the even larger and more prominent crater Grimaldi. To the southwest are the craters Hartwig and Schlüter that lie on the northeastern edge of Montes Cordillera, the ring-shaped range...

  • Grimaldi (crater)
    Grimaldi (crater)
    Grimaldi is a large basin located near the western limb of the Moon. It lies to the southwest of the Oceanus Procellarum, and southeast of the crater Riccioli...

External links

  • Brief Riccioli biography from the Catholic Encyclopedia
    Catholic Encyclopedia
    The Catholic Encyclopedia, also referred to as the Old Catholic Encyclopedia and the Original Catholic Encyclopedia, is an English-language encyclopedia published in the United States. The first volume appeared in March 1907 and the last three volumes appeared in 1912, followed by a master index...

  • Facts about Riccioli from Rice University
    Rice University
    William Marsh Rice University, commonly referred to as Rice University or Rice, is a private research university located on a heavily wooded campus in Houston, Texas, United States...

    's Galileo Project.
  • Riccioli, Giovanni Battista (French)