Giovanni Battista Riccioli

Italy, 1598-1671
Italian astronomer Giovanni Riccioli is known, among other things, for his experiments with pendulums and with falling bodies, for his discussion of 126 arguments concerning the motion of the Earth, and for introducing the current scheme of lunar nomenclature. Riccioli dealt not only with astronomy in his research, but also with physics, arithmetic, geometry, optics, gnomonics, geography, and chronology. Heentered the Society of Jesus 6 Oct., 1614. After teaching philosophy and theology for a number of years, chiefly at Parma and Bologna, he followed his superiors advice and devoted himself to the study of astronomy, which Kepler and Copernicus had made a hot topic. Riccioli ignored the misconceptions of the ancients and began to reconstruct astronomy from first principles. This led to his Almagestum novum, astronomiam veterem novamque complectens (1651), considered by many the most important literary work of the Jesuits during the seventeenth century. His most important contribution to astronomy was perhaps his detailed telescopic study of the moon, made in collaboration with P. Grimaldi. The latter’s excellent lunar map was inserted in the “Almagestum novum”, and the lunar nomenclature they adopted is still in use.

For example, he named large lunar areas such as the Mare Tranquillitatis, (the Sea of Tranquility, site of the Apollo 11 landing in 1969) 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”, and he named other important craters after other proponents of the Copernican theory such as Kepler, Galileo and Lansbergius.

Riccioli’s map also notes the moon is not inhabited. This countered speculations found in the works of Nicholas of Cusa, Giordano Bruno, and even Kepler, and even later writers like Bernard de Fontenelle and William Herschel.

Riccioli’s encyclopedic work consisted 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: John Flamsteed (1646–1719), the first English astronomer royal, a Copernican and a Protestant, used it for his Gresham lectures; Jérôme Lalande (1732–1807) of the Paris Observatory cited it extensively even though it was an old book at that point.

Within its two volumes were ten “books” covering every subject within astronomy:

1. the celestial sphere and subjects such as celestial motions, the equator, ecliptic, zodiac, etc.
2. the earth and its size, gravity and pendulum motion, etc.
3. the sun, its size and distance, its motion, observations involving it, etc.
4. the moon, its phases, its size and distance, etc. (detailed maps of the moon as seen through a telescope were included)
5. lunar and solar eclipses
6. the fixed stars
7. the planets and their motions, etc. (representations of each as seen with a telescope were included);
8. comets and novae (“new stars”)
9. the structure of the universe—the heliocentric and geocentric theories, etc.
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.  Riccioli is credited with being the first person to precisely measure the acceleration due to gravity of falling bodies.  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. He dropped equally weighted balls of wood and lead, noted the difference in descent times and knew to attribute the difference to air resistance, noting 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. Scrupulously factual, Riccioli’s descriptions also contained the text of Galileo’s condemnation. 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.”