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Johannes Phocylides Holwarda

Johannes Phocylides Holwarda (Jan Fokkesz, Jan Fokker, Johann Holwarda, Johannes Fokkes Holwarda, Jan Fokkens Holwarda, Jan Fokkes van haylen) (February 19, 1618—January 22, 1651)[1] was a Frisian astronomer, physician, and philosopher. He was a professor of philosophy at the University of Franeker from 1639 to 1651.[2]

Born in Holwerd, he is best remembered for his discovery of the length of Mira's (Omicron Ceti's) varying appearance cycle. In a systematic study in 1638, he found that Mira disappeared and reappeared in a varying cycle of about 330 days.[3][4]

Holwarda was also a supporter of "atomism". His Philosophia Naturalis, seu Physica Vetus-Nova, published posthumously in 1651, defines matter and form: matter is extended and divided into atoms while form is the texture of atoms. According to Phocylides, bodies are formed from atoms and a lack of atoms. Atoms, which he distinguished as simple or compound, are solid corpuscles that receive motion directly from God.[5]

The lunar crater Phocylides is named after him.[6]


  1. ^ Hockey, Thomas, ed. (2009). The Biographical Encyclopedia of Astronomers. Springer Publishing. ISBN 978-0-387-31022-0. Retrieved August 22, 2012.
  2. ^ Pieter Willem van der Horst, The Sentences of Pseudo-Phocylides (Brill, 1978), 63.
  3. ^ Holwarda, Johannes Phocylides
  4. ^ Mira, Omicron Ceti Archived 2007-10-24 at
  5. ^ Antonio Clericuzio, Elements, Principles and Corpuscles: A Study of Atomism and Chemistry in the Seventeenth Century (Springer, 2001), p. 187.
  6. ^ the-moon » Phocylides