A moon or not? A century of confusion

Part of the Science Networks. Historical Studies book series (SNHS, volume 37)


When Huygens made his observation of Titan revolving around Saturn, a satellite of Venus — meaning something that might be a satellite — had already been observed by an astronomer and instrument maker from Naples. However, during the following century the alleged satellite was seen only very rarely. Apart from Fontana’s original observation of 1645, it was seen in 1672 and 1686 by Cassini and then in 1740 by James Short in England. That was all. Understandably, at the time when preparations were made to observe the Venus transit across the Sun, predicted to occur on 6 June 1761, the existence of a Venus moon was controversial and enjoyed very little support.


Natural Philosopher Natural Theology Zodiacal Light Distant Planet Martian Moon 
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    See letter of Galileo to unknown correspondent, of 15 January 1639, in Galilei 1929–39, vol. 16, p. 18. See also Winkler and van Helden 1992, pp. 215–216.Google Scholar
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    Ibid., p. 91. Note that Fontana speaks in 1646 of a companion of Saturn, a decade before Huygens announced his discovery of Saturn’s moon. Fontana undoubtedly referred to the enigmatic appearance of what Galileo had originally called “stars” or “handles” (ansae) but which Huygens in 1659, in his Systema Saturnium, correctly interpreted as a thin ring surrounding the planet. The last sentence refers to the Aristotelian belief in crystalline spheres that were supposed to carry the planets.Google Scholar
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    The elusive ashen light continues to be somewhat of a puzzle as it is observed only occasionally and by some observers. In this respect, it shares some of the features of the Venus moon. On the history of the ashen light, see Hunt and Moore 1982, pp. 87–93, and Baum 2000.Google Scholar
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    Van Helden 1976b. Although Gassendi (1592–1655) was the only astronomer to publish his observation of the Mercury transit of 1631, it is known that several others saw the phenomenon, including Johannes Baptist Cysat (1588–1657), a student of Christopher Scheiner (1573–1650), and Johannes Remus Quietanus (fl. 1610–1640). The next Mercury transit visible in Europe, on 3 May 1661, was seen by Johannes Hevelius (1611–1687) in Danzig and also by Huygens during a stay in London.Google Scholar
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    Fontana 2001, p. 90. Zupus (1589–1667) taught mathematics in the Jesuit college in Naples for 27 years. His name is sometimes given as Zupo or Zupi.Google Scholar
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    For example, Frederik Kaiser (1802–1878), director of the Leiden Observatory, scornfully referred to “the silly explanation that the more distant planets are in need of many satellites in order to compensate for the sunlight.” He pointed out that such an explanation raised the question of why Mars had no moon. Kaiser 1867, p. 167, a Danish translation by Mathilde Ørsted, the daughter of H. C. Ørsted, of the third edition of Kaiser’s De Sterrenhemel (Leiden, 1860).Google Scholar
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    Quoted in Lambert 1776, p. 186. See also Schorr 1875, p. 65. Moore 1956, p. 93, mistakes Andreas Mayer (1716–1782) for the better known Tobias Mayer (1723–1762), the astronomer and cartographer at Göttingen University. (The error does not appear in Hunt and Moore 1982.) Nor is Andreas Mayer to be mixed up with the contemporary astronomer Christian Mayer (1719–1783), who did most of his work in Heidelberg. Greifswald in Pomerania came under Swedish rule in 1648, as a result of the Thirty Years War. In 1815 the city became part of Prussia.Google Scholar
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