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) was a Frisian

astronomer An astronomer is a scientist in the field of astronomy who focuses on a specific question or field outside the scope of Earth. Astronomers observe astronomical objects, such as stars, planets, natural satellite, moons, comets and galaxy, galax ...

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

University of Franeker The University of Franeker (1585–1811) was a university in Franeker, Friesland, the Netherlands. It was the second-oldest university of the Netherlands, founded shortly after Leiden University. History Also known as ''Academia Franekerensis'' ...

from 1639 to 1651. Born in Holwerd, he is best remembered for his discovery of the length of

Mira Mira (), designation Omicron Ceti (ο Ceti, abbreviated Omicron Cet, ο Cet), is a red-giant star estimated to be 200–300 light-years from the Sun in the constellation Cetus. ο Ceti is a binary stellar system, consisting of a vari ...

'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. Holwarda was also a supporter of "

atomism Atomism () is a natural philosophy proposing that the physical universe is composed of fundamental indivisible components known as atoms. References to the concept of atomism and its Atom, atoms appeared in both Ancient Greek philosophy, ancien ...

". His ''Philosophia Naturalis, seu Physica Vetus-Nova'', published posthumously in 1651, defines

matter In classical physics and general chemistry, matter is any substance that has mass and takes up space by having volume. All everyday objects that can be touched are ultimately composed of atoms, which are made up of interacting subatomic pa ...

and form: matter is extended and divided into atoms while form is the texture of

atoms Atoms are the basic particles of the chemical elements. An atom consists of a nucleus of protons and generally neutrons, surrounded by an electromagnetically bound swarm of electrons. The chemical elements are distinguished from each other ...

. 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 In monotheistic belief systems, God is usually viewed as the supreme being, creator, and principal object of faith. In polytheistic belief systems, a god is "a spirit or being believed to have created, or for controlling some part of the un ...

. The lunar

crater A crater is a landform consisting of a hole or depression (geology), depression on a planetary surface, usually caused either by an object hitting the surface, or by geological activity on the planet. A crater has classically been described ...

Phocylides Phocylides (), Greek gnomic poet of Miletus, contemporary of Theognis of Megara, was born about 560 BC. A few fragments of his " maxims" have survived (chiefly in the ''Florilegium'' of Stobaeus), in which he expresses his contempt for the po ...

is named after him.the-moon » Phocylides
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Notes

1618 births 1651 deaths Dutch Christians 17th-century Dutch astronomers Frisian scientists People from Dongeradeel Academic staff of the University of Franeker {{Europe-astronomer-stub