Helisaeus Roeslin or Helisäus Röslin (17 January 1545, Plieningen (now part of Stuttgart) – 14 August 1616, Buchsweiler was a German physician and astrologer who adopted a geoheliocentric model of the universe. He was one of five observers who concluded that the Great Comet of 1577 was located beyond the moon. His representation of the comet, described as "an interesting, though crude, attempt," was among the earliest and was highly complex.
Roeslin had known Johannes Kepler since their student days and was one of his correspondents. Roeslin placed more emphasis on astrological predictions than did Kepler, and though he respected Kepler as a mathematician, he rejected some of Kepler's cosmological principles, including Copernican theory. Kepler criticized Roeslin's predictions in his book De stella nova, on the comet of 1604, and the two kept up their arguments in a series of pamphlets written as dialogues.
Roeslin's 1597 book De opere Dei creationis is regarded as one of the major works in the late 16th-century controversy over the formulation of a geoheliocentric world system. Robert Burton refers to Roeslin in his Anatomy of Melancholy.
- Also Tycho Brahe, William IV, Landgrave of Hesse-Kassel, Cornelius Gemma, and Michael Mästlin.
- Robert S. Westman, "The Comet and the Cosmos: Kepler, Mästlin, and the Copernican Hypothesis," in The Reception of Copernicus' Heliocentric Theory: Proceedings of a Symposium Organized by the Nicolas Copernicus Committee of the International Union of the History and Philosophy of Science, Torun, Poland, 1973 (Springer, 1973), pp. 10 and 28. For a description and reproduction of the diagram, see pp. 28–29 online.
- Max Caspar, Kepler, translated and edited by C. Doris Hellman (New York: Dover, 1993), p. 181.
- Miguel Granada, "The Discussion between Kepler and Roeslin on the Nova of 1604," in 1604–2004: Supernovae as Cosmological Lighthouses, Astronomical Society of the Pacific Conference Series 342 (San Francisco 2005), as abstracted in a review by Alessandro Giostra.
- Gerd Fritz, "Dialogical Structures in 17th Century Controversies," p. 204, online.
- University of Cambridge Department of History and Philosophy of Science, "Conflict and Priority in Early-Modern Astronomy."
- Max Caspar, Kepler, p. 181.
- James Randi, The Mask of Nostradamus Page 240.
- Ole Peter Grell (1998). Paracelsus. p. 163.
- Akerman, Susanna. Rose Cross over the Baltic: The Spread of Rosicrucianism in Northern Europe. Brill 1998. Limited preview online.
- Caspar, Max. Kepler. Translated and edited by C. Doris Hellman. New York: Dover, 1993. Limited preview online.
- Granada, M.A. "Helisaeus Röslin on the eve of the appearance of the nova of 1604: his eschatological expectations and his intellectual career as recorded in the Ratio studiorum et operum meorum (1603-1604)." Sudhoffs Archiv 90 (2006) 75-96.
- Rosen, Edward. "Kepler's Attitude toward Astrology and Mysticism." In Occult and Scientific Mentalities in the Renaissance. Edited by Brian Vickers. Cambridge University Press, 1984. Limited preview online.