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 spoken by the Latins (Italic tribe), Latins in Latium (now known as Lazio), the lower Tiber area aroun ...

: "first movable") was the outermost moving

sphere A sphere (from Ancient Greek, Greek , ) is a surface (mathematics), surface analogous to the circle, a curve. In solid geometry, a sphere is the Locus (mathematics), set of points that are all at the same distance from a given point in three ...

in the

geocentric model In astronomy, the geocentric model (also known as geocentrism, often exemplified specifically by the Ptolemaic system) is a superseded scientific theories, superseded description of the Universe with Earth at the center. Under most geocentric m ...

of the

universe The universe is all of space and time and their contents. It comprises all of existence, any fundamental interaction, physical process and physical constant, and therefore all forms of matter and energy, and the structures they form, from s ...

. The concept was introduced by

Ptolemy Claudius Ptolemy (; , ; ; – 160s/170s AD) was a Greco-Roman mathematician, astronomer, astrologer, geographer, and music theorist who wrote about a dozen scientific treatises, three of which were important to later Byzantine science, Byzant ...

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 ( – 22 June 1037), commonly known in the West as Avicenna ( ), was a preeminent philosopher and physician of the Muslim world, flourishing during the Islamic Golden Age, serving in the courts of various Iranian peoples, Iranian ...

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heliocentric Heliocentrism (also known as the heliocentric model) is a Superseded theories in science#Astronomy and cosmology, superseded astronomical model in which the Earth and Solar System, planets orbit around the Sun at the center of the universe. His ...

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

Copernicus Nicolaus Copernicus (19 February 1473 – 24 May 1543) was a Renaissance polymath who formulated a mathematical model, model of Celestial spheres#Renaissance, the universe that placed heliocentrism, the Sun rather than Earth at its cen ...

– 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 the 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 Ancient Greek philos ...

on invisible orbs, while an eighth sphere contained the fixed

star A star is a luminous spheroid of plasma (physics), plasma held together by Self-gravitation, self-gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many other stars are visible to the naked eye at night sk ...

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

Empyrean In ancient European cosmologies inspired by Aristotle, the Empyrean heaven, Empyreal 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 philos ...

, 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 star ...

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

firmament In ancient near eastern cosmology, the firmament means a celestial barrier that separates the heavenly waters above from the Earth below. In biblical cosmology, the firmament ( ''rāqīaʿ'') is the vast solid dome created by God during the G ...

(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: Religion * Book of Genesis, the first book of the biblical scriptures of both Judaism and Christianity, describing the creation of the Earth and of humankind * Genesis creation narrative, the first several chapters of the Bo ...

1:7) is ninth, and the Primum Mobile is tenth. Outside all is the

, the "habitation of God and all the elect".

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), commonly referred to as Galileo Galilei ( , , ) or mononymously as Galileo, was an Italian astronomer, physicist and engineer, sometimes described as a poly ...

– 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) was an English philosopher and statesman who served as Attorney General and Lord Chancellor of England under King James I. Bacon argued for the importance of nat ...

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 of p ...

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 (; most likely baptized Durante di Alighiero degli Alighieri; – September 14, 1321), widely known mononymously as Dante, was an Italian Italian poetry, poet, writer, and philosopher. His ''Divine Comedy'', originally called ...

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 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), popularly known as W. B. Yeats, was an Irish poet, dramatist, writer, and literary critic who was one of the foremost figures of 20th-century literature. He was a driving force behind the ...

wrote: "The Primum Mobile that fashioned us / Has made the very owls in circles move." * John Ciardi wrote: "One night I dreamed I was locked in my Father's watch / With Ptolemy and twenty-one ruby stars / Mounted on spheres and the Primum Mobile / Coiled and gleaming to the end of space."

Appearance and rotation

Spherical variations

Copernicus and after

Literary references

See also

References

Further reading