Johannes Phocylides Holwarda (Jan Fokkesz, Jan Fokker, Johann Holwarda, Johannes Fokkes Holwarda, Jan Fokkens Holwarda, Jan Fokkes van Holwerd) (1618—January 22, 1651) was a Frisian

Frisians

The Frisians are a Germanic ethnic group native to the coastal parts of the Netherlands and Germany. They are concentrated in the Dutch provinces of Friesland and Groningen and, in Germany, East Frisia and North Frisia, that was a part of Denmark until 1864. They inhabit an area known as Frisia...

  astronomer

Astronomer

An astronomer is a scientist who studies celestial bodies such as planets, stars and galaxies.Historically, astronomy was more concerned with the classification and description of phenomena in the sky, while astrophysics attempted to explain these phenomena and the differences between them using...

, physician, and philosopher. He was professor of philosophy at the University of Franeker

University of Franeker

The University of Franeker was a university in Franeker, Friesland, presently part of the Netherlands. It was the second oldest university of the Netherlands, founded shortly after Leiden University....

 from 1639 to 1651.

Born in Holwerd

Holwerd

Holwerd is a village in the northern Netherlands, in the province of Friesland. Wadloopcentrum Fryslân in Holwerd is a center for the training of wadlopen guides and the preservation of the sport. It was the birthplace of astronomer Johannes Phocylides Holwarda. Holwerd had a station on the North...

, he is best remembered for his discovery of Mira

Mira

Mira also known as Omicron Ceti , is a red giant star estimated 200-400 light years away in the constellation Cetus. Mira is a binary star, consisting of the red giant Mira A along with Mira B. Mira A is also an oscillating variable star and was the first non-supernova variable star discovered,...

's (Omicron Ceti's) variation in brightness. In a systematic study in 1638, he found that Mira disappeared and reappeared in a varying cycle of about 330 days.

He was a supporter of “atomism

Atomism

Atomism is a natural philosophy that developed in several ancient traditions. The atomists theorized that the natural world consists of two fundamental parts: indivisible atoms and empty void.According to Aristotle, atoms are indestructible and immutable and there are an infinite variety of shapes...

”. His Philosophia Naturalis, seu Physica Vetus-Nova, published posthumously in 1651, defines matter

Matter

Matter is a general term for the substance of which all physical objects consist. Typically, matter includes atoms and other particles which have mass. A common way of defining matter is as anything that has mass and occupies volume...

 and form: matter is extended and divided into atoms while form is the texture of atoms. According to Phocylides, bodies are formed of atoms and void. Atoms, which he distinguished as simple or compound, are solid corpuscles that receive motion directly from God

God

God is the English name given to a singular being in theistic and deistic religions who is either the sole deity in monotheism, or a single deity in polytheism....

.

The lunar crater

Impact crater

In the broadest sense, the term impact crater can be applied to any depression, natural or manmade, resulting from the high velocity impact of a projectile with a larger body...

 Phocylides

Phocylides (crater)

Phocylides is a lunar crater located near the southwest rim of the Moon. It overlays the south rim of the crater Nasmyth to the north. To the northwest is the unusual plateau formation of Wargentin. Eastward is the merged formation Schiller, and in the southwest lies Pingré.The outer wall of...

is named after him.