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The Physics Teacher -- January 2012 -- Volume 50, Issue 1, pp. 18

Teaching Galileo? Get to Know Riccioli! What a Forgotten Italian Astronomer Can Teach Students About How Science Works

Christopher M. Graney

Jefferson Community & Technical College, Louisville, KY

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What can physics students learn about science from those scientists who got the answers wrong? Your students probably have encountered little science history. What they have encountered probably has portrayed scientists as “The People with the Right Answers.” But those who got the wrong answers can teach students that in science, answers are often elusive—not found in the back of a book or discovered in a bold stroke of genius.

© 2012 American Association of Physics Teachers

KEYWORDS and PACS

Keywords

astronomy, history, physics education, teaching

PACS

PUBLICATION DATA

ISSN

0031-921X (print)  

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$abstract.society.value is a Member of CrossRef American Association of Physics Teachers

ARTICLE DATA

Digital Object Identifier
http://dx.doi.org/10.1119/1.3670077

  1. Albert Einstein, “Foreword” in Galileo Galilei, Dialogue Concerning the Two Chief World Systems, Ptolemaic and Copernican, translated by Stillman Drake (Random House, New York, 2001), p. xxiii doi:10.1119/1.3488194PHTEAH000048000007000475000001.
  2. The LIFE Millenium: The 100 Most Important Events & People of the Past 1,000 Years, edited by Robert Friedman (Life Books, New York, 1998). LIFE ranked only Gutenberg, Columbus, Luther, and the Industrial Revolution ahead of Galileo.
  3. Riccioli created a pendulum with a precise half-period of one second by timing pendulums via the stars and very, very long sessions of counting swings (boosting a pendulum when its amplitude decreased too much). These included at least one 24-hour marathon session involving a team of counters (brothers from Riccioli's order—he was a Jesuit priest). Pendulums with shorter periods were calibrated from the seconds pendulum. To time balls falling from the 100-m tall Torre degli Asinelli in Bologna, Italy, he recruited a chorus of brothers to chant notes to the rhythm of the faster pendulums, creating an audible “timer” that could determine fall times to a high degree of accuracy. See J. L. Heilbron, The Sun in the Church: Cathedrals as Solar Observatories (Harvard University Press, 2001), pp. 180–81.
  4. Edward Grant, Planets, Stars, and Orbs: The Medieval Cosmos, 1200–1687 (Cambridge University Press, 1996), p. 652.
  5. Riccioli's map of the Moon, discussion of falling bodies, and 77 arguments are all found in his Almagestum Novum (Bologna, 1651), which is available online at www.e-rara.ch/zut/content/pageview/140188. It is very interestingto look at, even if you do not know Latin! An English summary of the 77 arguments is available on the Physics ArXiv (C. M. Graney, “Giovanni Battista Ricciolis Seventy-Seven Arguments Against the Motion of the Earth,” arXiv:1011.3778, arxiv.org/abs/1011.3778). All the references to Riccioli in this paper are from these sources.
  6. Argument #27 of the 77.
  7. See Dialogue, pp. 216–18.
  8. Argument #50 of the 77.
  9. “Forces and Fate,” New Sci. 209, 6 (Jan. 8, 2011).
  10. Because Galileo remarked in his Starry Messenger that stars seen through the telescope appear much the same as when seen by the naked eye, it is often said that Galileo and other astronomers understood stars to be dimensionless points of light. However, in his writings after the Starry Messenger, Galileo consistently said stars viewed with the telescope appeared as disks or spheres. See C. M. Graney, “Is magnification consistent?” Phys. Teach. 48, 475–477 (Oct. 2010).
  11. C. M. Graney, “The telescope against Copernicus: Star observations by Riccioli supporting a geocentric universe,” J. Hist. Astron. 41, 453–467 (2010).
  12. Christine Schofield, “The Tychonic and Semi-Tychonic World Systems,” in Planetary Astronomy from the Renaissance to the Rise of Astrophysics, edited by R. Taton and C. Wilson (Cambridge University Press, 1989), Part A, p. 39.
  13. Only two of the 77 anti-Copernican arguments Riccioli mentions dealt with religion, and he dismissed both.
  14. Owen Gingerich and J. R. Voelkel, “Tycho Brahe's Copernican campaign,” J. Hist. Astron. 29, 1–34 (1998), p. 24, p. 1.
  15. Direct evidence for Earth's motion would be discovered in 1728, when James Bradley detected “stellar aberration,” a deflection of starlight caused by Earth's motion around the Sun, by which time Newtonian physics had provided a full theoretical framework for underpinning the Copernican model. Full understanding of both the Coriolis effect and the Airy disk would elude physicists until the early 19th century, more than 150 years after the Almagestum Novum. Interestingly, the diffraction of light would be discovered and named by none other than Ricciolis assistant, Francesco Maria Grimaldi.
  16. Far more extreme ideas regarding science are not uncommon, especially the idea that a simple answer is known, but science is hiding it—whether “it” is the cause of increasing autism rates (vaccines); or the reason we have not returned to the Moon (aliens—unless it is that we never went to the Moon and NASA faked the whole thing in a studio); or the reason we don't have solar-powered cars (the technology is being suppressed by the energy companies). The vaccine issue, and the problem of public distrust of science in general, has been a recurring and recent topic on NPR's “Science Friday” talk show. See, for example, “Paul Offit and `Deadly Choices,'” Science Friday (Jan. 7, 2011); www.sciencefriday.com/program/archives/201101075). In all of these examples there is an implicit rejection of any sense that answers might be challenging and elusive in science; rather, the assumption is that the answer is known, but kept hidden.

Figures (click on thumbnails to view enlargements)

FIG.1
Maps of the Moon from Riccioli's 1651 Almagestum Novum, created by Riccioli and his assistant, Francesco Maria Grimaldi (1618–63). The names of prominent lunar features, such as the Sea of Tranquility, originated with these maps.

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FIG.2
Top — Diagram from the Almagestum Novum illustrating why a rotating Earth should cause deflection in the trajectory of a cannonball fired northward. Riccioli says that because the ball passes over slower-moving ground as it travels north, as seen from the cannon it will bend to the east, striking at G instead of at the intended point F. Bottom — Riccioli also argued that an object falling from a fixed point above the Earth would fall vertically if the Earth were immobile, but would arc to the east if Earth rotated (owing to the greater tangential speed of the object than of the point on Earth's surface directly below it). This diagram is actually from a 1679 letter from Isaac Newton to Robert Hooke (as shown in Walter William Rouse Ball's 1893 An Essay on Newton's “Principia”) proposing that Earth's movement could indeed be detected through this phenomenon, which prompted Hooke to try to do so (unsuccessfully).

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FIG.3
Sketch of a star seen through a small aperture telescope such as was used in much of the 17th century (from John Herschel's article on “Light” for the 1828 Encyclopaedia Metropolitana). This globe-like appearance, the spurious “Airy disk” formed by light diffracting through the telescope's aperture, was understandably interpreted by early telescopic astronomers (including Galileo) as the star's physical body. Riccioli argued that under the Copernican hypothesis (which required stars to be extremely distant), stars must be orders of magnitude larger than even the Sun to have such an appearance — thus the Copernican hypothesis was absurd.

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FIG.4
Frontispiece of the Almagestum Novum, showing Riccioli's assessment of the debate over whether the Earth moved. Mythological figures Argus (holding the telescope) and Urania (holding the scales) weigh the heliocentric hypothesis of Copernicus against a geo-heliocentric hypothesis such as Tycho Brahe promoted. The old purely geocentric model, in which everything circles the Earth, lies discarded on the ground, disproven by discoveries made with the telescope. These discoveries, which include phases of Venus and moons of Jupiter, are illustrated at top left and right. The balance tips in favor of the geo-heliocentric hypothesis, showing Riccioli's opinion about how the debate stood at the time. (Image courtesy History of Science Collections, University of Oklahoma Libraries.)

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FIG.5
Illustration from the 1742 Atlas Coelestis by J. G. Dopplmayer and J. B. Homann (compare to Fig. 4). The old purely geocentric model is shown as broken under the telescope and discarded; the choice for scientists is between the heliocentric and geo-heliocentric hypotheses. Here, however, it is the heliocentric that is shown as being the better choice. But a significant portion of the Atlas Coelestis is devoted to the geoheliocentric hypothesis. A hypothesis with an immobile Earth had staying power a full century after Galileo. (Image courtesy of R. H. van Gent.)

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