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 their studies on a specific question or field outside the scope of Earth. They observe astronomical objects such as stars, planets, natural satellite, moons, comets and galaxy, g ...

, 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'' o ...

from 1639 to 1651. Born in

Holwerd Holwert is a village in Noardeast-Fryslân municipality in the northern Netherlands, in the province of Friesland. It had a population of around 1,607 in January 2017. Before 2019, the village was part of the Dongeradeel municipality. The ferry to ...

, 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 200–400 light-years from the Sun in the constellation Cetus. ο Ceti is a binary stellar system, consisting of a varia ...

'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 (from Greek , ''atomon'', i.e. "uncuttable, indivisible") 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 atoms ...

". 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 partic ...

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

atoms Every atom is composed of a nucleus and one or more electrons bound to the nucleus. The nucleus is made of one or more protons and a number of neutrons. Only the most common variety of hydrogen has no neutrons. Every solid, liquid, gas, an ...

. 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 monotheism, monotheistic thought, God is usually viewed as the supreme being, creator deity, creator, and principal object of Faith#Religious views, faith.Richard Swinburne, Swinburne, R.G. "God" in Ted Honderich, Honderich, Ted. (ed)''The Ox ...

. The lunar

crater Crater may refer to: Landforms *Impact crater, a depression caused by two celestial bodies impacting each other, such as a meteorite hitting a planet *Explosion crater, a hole formed in the ground produced by an explosion near or below the surfac ...

Phocylides Phocylides ( el, Φωκυλίδης ὁ Μιλήσιος), 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 ...

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 University of Franeker faculty {{Europe-astronomer-stub