In classical, medieval, and Renaissance astronomy, the Primum Mobile (

Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around present-day Rome, but through ...

: "first movable") was the outermost moving

sphere A sphere () is a geometrical object that is a three-dimensional analogue to a two-dimensional circle. A sphere is the set of points that are all at the same distance from a given point in three-dimensional space.. That given point is the c ...

in the

geocentric model In astronomy, the geocentric model (also known as geocentrism, often exemplified specifically by the Ptolemaic system) is a superseded description of the Universe with Earth at the center. Under most geocentric models, the Sun, Moon, stars, an ...

of the

universe The universe is all of space and time and their contents, including planets, stars, galaxies, and all other forms of matter and energy. The Big Bang theory is the prevailing cosmological description of the development of the univers ...

. The concept was introduced by

Ptolemy Claudius Ptolemy (; grc-gre, Πτολεμαῖος, ; la, Claudius Ptolemaeus; AD) was a mathematician, astronomer, astrologer, geographer, and music theorist, who wrote about a dozen scientific treatises, three of which were of importanc ...

to account for the apparent daily motion of the heavens around the Earth, producing the east-to-west rising and setting of the sun and stars, and reached Western Europe via

Avicenna Ibn Sina ( fa, ابن سینا; 980 – June 1037 CE), commonly known in the West as Avicenna (), was a Persian polymath who is regarded as one of the most significant physicians, astronomers, philosophers, and writers of the Islamic ...

Appearance and rotation

The Ptolemaic system presented a view of the universe in which apparent motion was taken for real – a viewpoint still maintained in common speech through such everyday terms as ''moonrise'' and ''sunset''. Rotation of the Earth on its polar axis – as seen in a

heliocentric Heliocentrism (also known as the Heliocentric model) is the astronomical model in which the Earth and planets revolve around the Sun at the center of the universe. Historically, heliocentrism was opposed to geocentrism, which placed the Earth ...

solar system, which (while anticipated by Aristarchus) was not to be widely accepted until well after

Copernicus Nicolaus Copernicus (; pl, Mikołaj Kopernik; gml, Niklas Koppernigk, german: Nikolaus Kopernikus; 19 February 1473 – 24 May 1543) was a Renaissance polymath, active as a mathematician, astronomer, and Catholic canon, who formulat ...

– leads to what earlier astronomers saw as the real movement of all the heavenly bodies around the Earth every 24 hours. Astronomers believed that the seven naked-eye planets (including the Moon and the Sun) were carried around the

spherical Earth Spherical Earth or Earth's curvature refers to the approximation of figure of the Earth as a sphere. The earliest documented mention of the concept dates from around the 5th century BC, when it appears in the writings of Greek philosophers. ...

on invisible orbs, while an eighth sphere contained the fixed

star A star is an astronomical object comprising a luminous spheroid of plasma (physics), plasma held together by its gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many other stars are visible to the naked ...

s. Motion was provided to the whole system by the Primum Mobile, itself set within the

Empyrean In ancient cosmologies, the Empyrean Heaven, or simply the Empyrean, was the place in the highest heaven, which was supposed to be occupied by the element of fire (or aether in Aristotle's natural philosophy). The word derives from the Mediev ...

, and the fastest moving of all the spheres.

Spherical variations

The total number of

celestial spheres The celestial spheres, or celestial orbs, were the fundamental entities of the cosmological models developed by Plato, Eudoxus, Aristotle, Ptolemy, Copernicus, and others. In these celestial models, the apparent motions of the fixed stars ...

was not fixed. In this 16th-century illustration, the

firmament In biblical cosmology, the firmament is the vast solid dome created by God during his creation of the world to divide the primal sea into upper and lower portions so that the dry land could appear. The concept was adopted into the subsequent ...

(sphere of fixed stars) is eighth, a "crystalline" sphere (posited to account for the reference to "waters ... above the firmament" in

Genesis Genesis may refer to: Bible * Book of Genesis, the first book of the biblical scriptures of both Judaism and Christianity, describing the creation of the Earth and of mankind * Genesis creation narrative, the first several chapters of the Book of ...

1:7) is ninth, and the Primum Mobile is tenth. Outside all is the Empyrean, the "habitation of God and all the

elect An election is a formal group decision-making process by which a population chooses an individual or multiple individuals to hold public office. Elections have been the usual mechanism by which modern representative democracy has operated ...

Copernicus and after

Copernicus accepted existence of the sphere of the fixed stars, and (more ambiguously) that of the Primum Mobile, as too (initially) did

Galileo Galileo di Vincenzo Bonaiuti de' Galilei (15 February 1564 – 8 January 1642) was an Italian astronomer, physicist and engineer, sometimes described as a polymath. Commonly referred to as Galileo, his name was pronounced (, ). He was ...

– though he would later challenge its necessity in a heliocentric system.

Francis Bacon Francis Bacon, 1st Viscount St Alban (; 22 January 1561 – 9 April 1626), also known as Lord Verulam, was an English philosopher and statesman who served as Attorney General and Lord Chancellor of England. Bacon led the advancement of both ...

was as sceptical of the Primum Mobile as he was of the rotation of the earth. Once

Kepler Johannes Kepler (; ; 27 December 1571 – 15 November 1630) was a German astronomer, mathematician, astrologer, natural philosopher and writer on music. He is a key figure in the 17th-century Scientific Revolution, best known for his laws o ...

had made the sun, not the Primum Mobile, the cause of planetary motion, however, the Primum Mobile gradually declined into the realm of metaphor or literary allusion.

Literary references

Dante Dante Alighieri (; – 14 September 1321), probably baptized Durante di Alighiero degli Alighieri and often referred to as Dante (, ), was an Italian poet, writer and philosopher. His ''Divine Comedy'', originally called (modern Italian: ' ...

made the Primum Mobile the ninth of the ten heavens into which he divided his '' Paradiso''. *In

Geoffrey Chaucer Geoffrey Chaucer (; – 25 October 1400) was an English poet, author, and civil servant best known for '' The Canterbury Tales''. He has been called the "father of English literature", or, alternatively, the "father of English poetry". He w ...

's "

Man of Law's Tale "The Man of Law's Tale" is the fifth of the ''Canterbury Tales'' by Geoffrey Chaucer, written around 1387. John Gower's "Tale of Constance" in ''Confessio Amantis'' tells the same story and may have been a source for Chaucer. Nicholas Trivet ...

", the Primum Mobile is apostrophized: "O firste moevyng! crueel firmament, / With thy diurnal sweigh that crowdest ay / And hurlest al from est til occident / That naturelly wolde holde another way ..." (ll. 295–298). *

W. B. Yeats William Butler Yeats (13 June 186528 January 1939) was an Irish poet, dramatist, writer and one of the foremost figures of 20th-century literature. He was a driving force behind the Irish Literary Revival and became a pillar of the Irish liter ...

wrote: "The Primum Mobile that fashioned us / Has made the very owls in circles move."W. B. Yeats, ''The Poems'' (1984) p. 203.

References

{{Reflist, 2}

Appearance and rotation

Spherical variations

Copernicus and after

Literary references

See also

References

Further reading