Govaert Wendelen (6 June 1580 – 24 October 1667) was a Flemish astronomer who was born in Herk-de-Stad. He is also known by the Latin name Vendelinus. His name is sometimes given as Godefroy Wendelin; his first name spelt Godefroid or Gottfried.
Around 1630 he measured the distance between the Earth and the Sun using the method of Aristarchus of Samos. The value he calculated was 60% of the true value (243 times the distance to the Moon; the true value is about 384 times; Aristarchus calculated about 20 times).
The crater Vendelinus on the Moon is named after him.
Wendelin died in Ghent on 24 October 1667.
- (1626) Loxias seu de obliquitate solis, Antwerp, apud Hieronymum Verdussium;
- (1632) Aries seu Aurei Velleris encomium ;
- (1637) De tetracty Pythagorae dissertatio epistolica, ad Erycium Puteanum ;
- (1643) Arcanorum caelestium Lampas τετράλυχνος, Brussels;
- (1644) Eclipses lunares ab anno 1573 ad 1643 observatae, Antwerp, apud Hieronymum Verdussium;
- (1649) Leges salicae illustratae, Antwerp;
- (1652) Teratologia cometica ;
- (1655) De causis naturalibus, pluviae purpureae Bruxellensis, London;
- (1658) Arcanorum caelestium Sphinx et Oedipus seu Lampas δωδεκράλυχνος, Tournai.
- (1629) De diluvio liber primus, Antwerp;
- (1629) De diluvio liber secundus (incomplete);
- (1630) Parapegma ou Kalendrier pour l’an de Iesus Christ MDCXXXI ;
- (1636) In id Psalmorum “Salvabis, Domine, homines et iumenta et lebes spei meae” ;
- (1643) Censura et iudicium de falsitate Bruxellensis ;
- (1647) Pluviae purpureae Bruxellensis, Paris;
- (1655) Duorum eminentissimorum S.R.E. luminum Petri Aloysii Carafae ;
- (1655) Clementis apostoli Epistolarum encycliarum altera ;
- (1655) Epistola didactica de Calcedonio lapide seu gemma gnostica ;
- (1659) Gnome orthodoxa temporum sacrorum inde a Petro apostolorum principe ad Alexandrum VII usque usitatorum.
- Wendelin is also the author of an anonymous pamphlet (32 pages) on local political bickering in Herk during his pastorate there. Printed without title, date or address (probably Liège, Christian Ouwerk, 1645), it begins with La Ville de Wuest-Herck, que les anciens documens... escriuent Harck (Welkenhuysen, 2000:445).
- There is some ambiguity about exactly when Wendelin recognized that Jupiter's moons obey Kepler's third law.
Pierre Costabel states that the scholarly world learned of Wendelin's discovery in 1651, when the Italian cleric and astronomer Giovanni Battista Riccioli (1598-1671) published his book Almagestum novum … . From page 107 of Anne Reinbold, ed., Peiresc, ou, La passion de connaître (Peiresc, or the Passion to Know) (Paris, France: J. Vrin, 1990): "Car le fait indéniable est le suivant: c'est par la publication de Riccioli que le milieu savant a été informé en 1651 de ce que la troisième loi de Kepler était applicable aux satellites de Jupiter, et cela d'après Wendelin." (For the undeniable fact is the following: it was by Riccioli's publication that the scholarly world was informed in 1651 that Kepler's third law was applicable to Jupiter's satellites, and that according to Wendelin.)
In volume 1 of Riccioli's Almagestum novum … (Bologna ("Bononiæ"), (Italy): Victor Benati, 1651), page 492 (lower right corner), Riccioli presents the ratios of the distances of the moons from Jupiter and their periods, and he states that the period of each moon is proportional to the three-halves power of its distance from Jupiter. He credits this relation to Wendelin ("Vendelini").
In volume 2 of his Almagestum novum, page 532 (upper right side), Riccioli again credits this relation to Wendelin: "… proportionem inter periodos & intervalla Satellitum Jovis a Jove adnotavit Vedelinus in sua doctissima epistola ad me ab ipso perscripta." (… in his most learned letter written to me by him, Wendelin noted the ratios between the periods and distances of Jupiter's satellites from Jupiter.)
In volume 1 of his Astronomia Reformata (Bologna ("Bononiæ"), (Italy): Victor Benati, 1665), page 371 (upper left corner of page), Riccioli discusses the position and motion of the moons of Jupiter (Situs & Motus Satellitum Jovis) and cites Wendelin as one of his sources: "… ex Vuendelini Epistola ad me, …" (… from Wendelin's letter to me, …). On the same page (center of right side), Riccioli again credits "Vuendelinus" with showing that Jupiter's moons obey Kepler's third law: "… ita Planetulorum Jovialium distantias a Jove, esse in ratione sequialtera suorum temporum periodicorum." (… so the three-halves power of the distances of Jupiter’s satellites from Jupiter, to be in the ratio of their periodic times.) On page 370 (near end of paragraph 4 on right side of page), during a discussion of the number of moons of Jupiter (De Numero Satellitum Jovis), he cites as a source: "Deniq; Vuendelinus in Epistola ad me anni 1647." (Finally; Wendelin in a letter to me in the year 1647.)
This might suggest that Wendelin made his discovery in the 1640s. However, Pierre Costabel — in his essay, Peiresc et Wendelin: les satellites de Jupiter de Galilée à Newton (Peiresc and Wendelin: Jupiter's satellites from Galileo to Newton), which was published in Anne Reinbold, ed., Peiresc, ou, La passion de connaître (Paris, France: J. Vrin, 1990) — states that Peiresc (1580-1637) made observations of Jupiter's moons in 1610 (see pages 95ff), at which time Wendelin was living near Peiresc, and that by 1624, Wendelin was using Peiresc's data to construct tables of the motions of Jupiter's moons, so that navigators could determine their longitude (see page 104).
- Johannes Kepler recognized at least as early as 1622 that Jupiter's moons obey his third law.
Kepler contended that rotating massive bodies communicate their rotation to their satellites, so that the satellites are swept around the central body; thus the rotation of the Sun drives the revolutions of the planets and the rotation of the Earth drives the revolution of the Moon. In Kepler's era, no one had any evidence of Jupiter's rotation. However, Kepler argued that the force by which a central body causes its satellites to revolve around it, weakens with distance; consequently, satellites that are farther from the central body revolve slower. Kepler noted that Jupiter's moons obeyed this pattern and he inferred that a similar force was responsible. He also noted that the orbital periods and semi-major axes of Jupiter's satellites were roughly related by a 3/2 power law, as are the orbits of the six (then known) planets. However, this relation was approximate: the periods of Jupiter's moons were known within a few percent of their modern values, but the moons’ semi-major axes were determined less accurately.
Kepler discussed Jupiter's moons in his Epitome Astronomiae Copernicanae [Epitome of Copernican Astronomy] (Linz (“Lentiis ad Danubium“), (Austria): Johann Planck, 1622), book 4, part 2, page 554. (For a more modern and legible edition, see: Christian Frisch, ed., Joannis Kepleri Astronomi Opera Omnia, vol. 6 (Frankfurt-am-Main, (Germany): Heyder & Zimmer, 1866), page 361.)
Original : 4) Confirmatur vero fides hujus rei comparatione quatuor Jovialium et Jovis cum sex planetis et Sole. Etsi enim de corpore Jovis, an et ipsum circa suum axem convertatur, non ea documenta habemus, quae nobis suppetunt in corporibus Terrae et praecipue Solis, quippe a sensu ipso: at illud sensus testatur, plane ut est cum sex planetis circa Solem, sic etiam se rem habere cum quatuor Jovialibus, ut circa corpus Jovis quilibet, quo longius ab illo potest excurrere, hoc tardius redeat, et id quidem proportione non eadem, sed majore, hoc est sescupla proportionis intervallorum cujusque a Jove: quae plane ipsissima est, qua utebantur supra sex planetae. Intervalla enim quatuor Jovialium a Jove prodit Marius in suo Mundo Joviali ista: 3, 5, 8, 13 (vel 14 Galilaeo) … Periodica vero tempora prodit idem Marius ista: dies 1. h. 18 1/2, dies 3 h. 13 1/3, dies 7 h. 3, dies 16 h. 18: ubique proportio est major quam dupla, major igitur quam intervallorum 3, 5, 8, 13 vel 14, minor tamen quam quadratorum, qui duplicant proportiones intervallorum, sc. 9, 25, 64, 169 vel 196, sicut etiam sescupla sunt majora simplis, minora vero duplis.
Translation : (4) However, the credibility of this [argument] is proved by the comparison of the four [moons] of Jupiter and Jupiter with the six planets and the Sun. Because, regarding the body of Jupiter, whether it turns around its axis, we don't have proofs for what suffices for us [regarding the rotation of ] the body of the Earth and especially of the Sun, certainly [as reason proves to us]: but reason attests that, just as it is clearly [true] among the six planets around the Sun, so also it is among the four [moons] of Jupiter, because around the body of Jupiter any [satellite] that can go farther from it orbits slower, and even that [orbit's period] is not in the same proportion, but greater [than the distance from Jupiter]; that is, 3/2 (sescupla ) of the proportion of each of the distances from Jupiter, which is clearly the very [proportion] as [is used for] the six planets above. In his [book] The World of Jupiter [Mundus Jovialis, 1614], [Simon] Mayr [1573-1624] presents these distances, from Jupiter, of the four [moons] of Jupiter: 3, 5, 8, 13 (or 14 [according to] Galileo) … Mayr presents their time periods: 1 day 18 1/2 hours, 3 days 13 1/3 hours, 7 days 3 hours, 16 days 18 hours: for all [of these data] the proportion is greater than double, thus greater than [the proportion] of the distances 3, 5, 8, 13 or 14, although less than [the proportion] of the squares, which double the proportions of the distances, namely 9, 25, 64, 169 or 196, just as [a factor of] 3/2 is also greater than 1 but less than 2.
- Sacré, D., and G. Tournoy (2000) Myricae: Essays on Neo-Latin Literature in Memory of Jozef Ijsewijn, Leuven University Press.
- Le Paige,C. Un astronome belge: Godefroid Wendelin. (In French.)
- Silveryser, F. Godefroid Wendelen. Sa vie, son ambiance et ses travaux (Tongres, 1934 [=1936]), reprinted from Bulletin de l’Institut Archéologique Liégeois, 58, 1934, p. 91-158, and 60, 1936, p. 137-190. (In French.)
- Zwartebroeckx, H. J., ‘Wendelen (Wendelinus), Godfried’, in Nationaal biografischwoordenboek, 4 (1970), cc. 944-951 [esp. 951]. (In Dutch.)