Dörffel, Georg Samuel
Born Plauen, (Sachsen, Germany), 21 November 1643
Died Weida, (Thuringen, Germany), 6–16 August 1688
Georg Dörffel’s contributions to astronomy concern, above all, investigations into the orbits of planets and comets. Dörffel was the son of an evangelical clergyman. His father had studied in Frankfurt an der Oder, Königsberg, in Denmark, Holland, and Sweden. He became the private tutor and envoy for the prince electors of Brandenburg, and also worked as a country pastor in a few villages around Plauen. Dörffel’s mother had been twice married but had lost her previous husbands to the plague. Georg Dörffel was the only one of four children to reach adulthood. He attended the city school in Plauen and studied in Leipzig and afterward in Jena. Studying under Erhard Weigel , he obtained his master’s degree in 1663 by defending his thesis entitled Exercitatio philosophica de quantitate motus gravium. Dörffel concluded his studies in 1667 by receiving a bachelor of theology from the University of Leipzig.
After his father’s death in 1672, Dörffel established himself as a successful rural clergyman and priest, having to give more than 100 sermons a year. In 1684, he was appointed superintendent in Thuringia by the rulers of Saxe-Zeitz. After the death of his first two wives, Dörffel married a third time, a marriage that produced ten children.
Dörffel’s interest in astronomy was already apparent at a very early age. His first two astronomical works, published in 1672, dealt with that year’s comet (C/1672 E1) and were followed by five more astronomical studies in 1677, 1680, 1681, and 1682. The subsequent publications contained observations about the total lunar eclipse of 21 February 1682, the mathematical prediction of the lunar eclipse on 27 June 1684, the “Neue Mondwunder” (the appearance of a halo) on 24 January 1684, and a study of the principles governing the parallaxes of the planets and comets. Preserved in manuscript are Dörffel’s calculations of the path of the fireball on 22 August 1683, which he compiled based on observations made by both himself and others, and which illustrate Dörffel’s efforts in studying a phenomenon that had hardly been considered previously. In addition, astronomy always remained for him a leisure activity that he could practice only after he had completed his professional duties, which he took very seriously.
Although the cosmic nature of comets was recognized in the mid-seventeenth century (especially by the successors to Tycho Brahe and Christoph Rothmann ), the form of their movement remained unknown, even when it was accepted around 1600 that they had orbits resembling those of the planets (e.g., by Helisaeus Roeslin and Johannes Krabbe).
The comet discovered by Gottfried Kirch on 14 November 1680, C/1680 V1, fueled investigations into the principal assumptions about comet orbits. The 1680 event could be observed both before (24 November 1680) and after its passage through perihelion (on 11 December 1680). However, the first problem consisted in recognizing the appearance of one and the same comet. Most astronomers (as well as Kirch himself) believed that there were two comets – one in the evening sky and another in the morning sky.
The observations of comets in 1680 and 1681 did not involve two comets but two appearances of a single comet moving around the Sun. Dörffel refers, in this research, to Occam’s razor, i.e., “one thing should not be made many without it being necessary.”
The orbit of this comet is a parabola, in which the Sun occupies the focal point. Only by assuming the existence of a single comet is it possible to recognize the parabolic movement of this heavenly body. By assuming the existence of two comets, earlier researchers were led to believe that comets had a linear or, at best, a slightly bent path.
As the comet C/1680 V1 was a so called sungrazer, its orbit did, in fact, very strongly approximate the form of a parabola, as a result of which Dörffel was proven right in this case. The deduction of the parabolic orbit of the comet gives the focal point of the orbit, the point occupied by the Sun, a special significance.
Concerning the nature of comets themselves, Dörffel appeared temporarily to agree with notions describing them as “disks,” such as the one advanced by Johannes Hevel . He had not found a parallax and was convinced by others, insofar as he held comets to be heavenly bodies. His avowal of Nicolaus Copernicus was a hesitant one, and he had earlier also refused to accept Brahe’s geo-heliocentric system.
Dörffel settled questions about the orbits of comets on primarily empirical grounds, on the basis of his own observations, and found the correct means of describing the orbit of comet C/1680 V1. However, this discovery subsequently received little recognition, especially since Isaac Newton established, a little later, the correct methods of describing the motion of heavenly bodies. Only at the end of the eignteenth century was Dörffel’s achievement appreciated by German and French astronomers, and his lasting significance in the history of astronomy made apparent. In addition to his astronomical studies, Dörffel published several theological works including at least one funeral sermon and a book on the Hebraic language (Tirocinium accentuationis, ad lectionem Biblicam practice accomodatum, Plauen, 1670).
- Hamel, Jürgen (1994). “Die Vorstellung von den Kometen seit der Antike bis in 17. Jahrhundert - Tradition und Innovation.” In Georg Samuel Dörffel (1643–1688): Theologe und Astronom. Plauen: Vogtland-Verlag, pp. 97–122.Google Scholar
- Hellmann, C. Doris (1971). “Dörffel, Georg Samuel.” In Dictionary of Scientific Biography, edited by Charles Coulston Gillispie. Vol. 4, pp. 168–169. New York: Charles Scribner’s Sons.Google Scholar
- Pfitzner, Elvira (1998). Die astronomischen Beobachtungen des Geistlichen Georg Samuel Dörffel. Weissbach: Beir and Beran. (See pp. 37–40 for a bibliography of Dörffel’s writings.)Google Scholar
- Reinhard, C. (1882). “Dörffel, Georg Samuel. Ein Beitrag zur Geschichte der Astronomie im 17. Jahrhundert.” Mitteilungen(Altertumsverein Plauen) 2: 1–77.Google Scholar
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