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The center of the Universe is a concept that lacks a coherent definition in modern
astronomy Astronomy () is a natural science that studies celestial objects and phenomena. It uses mathematics, physics, and chemistry in order to explain their origin and evolution. Objects of interest include planets, moons, stars, nebulae, g ...
; according to standard
cosmological Cosmology () is a branch of physics and metaphysics dealing with the nature of the universe. The term ''cosmology'' was first used in English in 1656 in Thomas Blount's ''Glossographia'', and in 1731 taken up in Latin by German philosopher ...
theories on the
shape of the universe The shape of the universe, in physical cosmology, is the local and global geometry of the universe. The local features of the geometry of the universe are primarily described by its curvature, whereas the topology of the universe describes ge ...
, it has no center. Historically, different people have suggested various locations as the center of the Universe. Many mythological cosmologies included an ''
axis mundi In astronomy, axis mundi is the Latin term for the axis of Earth between the celestial poles. In a geocentric coordinate system, this is the axis of rotation of the celestial sphere. Consequently, in ancient Greco-Roman astronomy, the ' ...
'', the central axis of a flat Earth that connects the Earth, heavens, and other realms together. In the 4th century BC Greece, philosophers developed 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the geocentric model (also known as geocentrism, often exemplified specifically by the Ptolemaic system) is a superseded description of the Universe with Earth at the center.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 ...
, based on astronomical observation; this model proposed that the center of the Universe lies at the center of a spherical, stationary Earth, around which the Sun, Moon, planets, and stars rotate. With the development of the
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 ...
model by
Nicolaus 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 ...
in the 16th century, the Sun was believed to be the center of the Universe, with the planets (including Earth) and stars orbiting it. In the early-20th century, the discovery of other
galaxies A galaxy is a system of stars, stellar remnants, interstellar gas, dust, dark matter, bound together by gravity. The word is derived from the Greek ' (), literally 'milky', a reference to the Milky Way galaxy that contains the Solar System ...
and the development of the
Big Bang theory The Big Bang event is a physical theory that describes how the universe expanded from an initial state of high density and temperature. Various cosmological models of the Big Bang explain the evolution of the observable universe from the ...
led to the development of cosmological models of a homogeneous, isotropic Universe, which lacks a central point and is expanding at all points.


Outside astronomy

In religion or mythology, the ''
axis mundi In astronomy, axis mundi is the Latin term for the axis of Earth between the celestial poles. In a geocentric coordinate system, this is the axis of rotation of the celestial sphere. Consequently, in ancient Greco-Roman astronomy, the ' ...
'' (also cosmic axis, world axis, world pillar, columna cerului, center of the world) is a point described as the center of the world, the connection between it and Heaven, or both.
Mount Hermon Mount Hermon ( ar, جبل الشيخ or جبل حرمون / ALA-LC: ''Jabal al-Shaykh'' ("Mountain of the Sheikh") or ''Jabal Haramun''; he, הַר חֶרְמוֹן, ''Har Hermon'') is a mountain cluster constituting the southern end of th ...
was regarded as the axis mundi in Canaanite tradition, from where the
sons of God Sons of God ( he, בְנֵי־הָאֱלֹהִים, Bənē hāʾĔlōhīm, literally: "sons of the Elohim") is a phrase used in the Tanakh or Old Testament and in Christian Apocrypha. The phrase is also used in Kabbalah where ''bene elohim'' ...
are introduced descending in 1 Enoch (1En6:6). The
ancient Greeks Ancient Greece ( el, Ἑλλάς, Hellás) was a northeastern Mediterranean civilization, existing from the Greek Dark Ages of the 12th–9th centuries BC to the end of classical antiquity ( AD 600), that comprised a loose collection of cult ...
regarded several sites as places of earth's ''
omphalos An omphalos is a religious stone artifact, or baetylus. In Ancient Greek, the word () means "navel". Among the Ancient Greeks, it was a widespread belief that Delphi was the center of the world. According to the myths regarding the founding of ...
'' (navel) stone, notably the oracle at
Delphi Delphi (; ), in legend previously called Pytho (Πυθώ), in ancient times was a sacred precinct that served as the seat of Pythia, the major oracle who was consulted about important decisions throughout the ancient classical world. The orac ...
, while still maintaining a belief in a cosmic
world tree The world tree is a motif present in several religions and mythologies, particularly Indo-European religions, Siberian religions, and Native American religions. The world tree is represented as a colossal tree which supports the heavens, thereb ...
and in
Mount Olympus Mount Olympus (; el, Όλυμπος, Ólympos, also , ) is the highest mountain in Greece. It is part of the Olympus massif near the Thermaic Gulf of the Aegean Sea, located in the Olympus Range on the border between Thessaly and Macedonia, be ...
as the abode of the gods. Judaism has the
Temple Mount The Temple Mount ( hbo, הַר הַבַּיִת, translit=Har haBayīt, label=Hebrew, lit=Mount of the House f the Holy}), also known as al-Ḥaram al-Sharīf (Arabic: الحرم الشريف, lit. 'The Noble Sanctuary'), al-Aqsa Mosque compou ...
and
Mount Sinai Mount Sinai ( he , הר סיני ''Har Sinai''; Aramaic: ܛܘܪܐ ܕܣܝܢܝ ''Ṭūrāʾ Dsyny''), traditionally known as Jabal Musa ( ar, جَبَل مُوسَىٰ, translation: Mount Moses), is a mountain on the Sinai Peninsula of Egypt. It ...
, Christianity has the
Mount of Olives The Mount of Olives or Mount Olivet ( he, הַר הַזֵּיתִים, Har ha-Zeitim; ar, جبل الزيتون, Jabal az-Zaytūn; both lit. 'Mount of Olives'; in Arabic also , , 'the Mountain') is a mountain ridge east of and adjacent to Jeru ...
and
Calvary Calvary ( la, Calvariae or ) or Golgotha ( grc-gre, Γολγοθᾶ, ''Golgothâ'') was a site immediately outside Jerusalem's walls where Jesus was said to have been crucified according to the canonical Gospels. Since at least the early medie ...
, Islam has
Mecca Mecca (; officially Makkah al-Mukarramah, commonly shortened to Makkah ()) is a city and administrative center of the Mecca Province of Saudi Arabia, and the holiest city in Islam. It is inland from Jeddah on the Red Sea, in a narrow v ...
, said to be the place on earth that was created first, and the
Temple Mount The Temple Mount ( hbo, הַר הַבַּיִת, translit=Har haBayīt, label=Hebrew, lit=Mount of the House f the Holy}), also known as al-Ḥaram al-Sharīf (Arabic: الحرم الشريف, lit. 'The Noble Sanctuary'), al-Aqsa Mosque compou ...
(
Dome of the Rock The Dome of the Rock ( ar, قبة الصخرة, Qubbat aṣ-Ṣakhra) is an Islamic shrine located on the Temple Mount in the Old City of Jerusalem, a site also known to Muslims as the ''al-Haram al-Sharif'' or the Al-Aqsa Compound. Its initial ...
). In
Shinto Shinto () is a religion from Japan. Classified as an East Asian religion by scholars of religion, its practitioners often regard it as Japan's indigenous religion and as a nature religion. Scholars sometimes call its practitioners ''Shint ...
, the
Ise Shrine The , located in Ise, Mie Prefecture of Japan, is a Shinto shrine dedicated to the sun goddess Amaterasu. Officially known simply as , Ise Jingū is a shrine complex composed of many Shinto shrines centered on two main shrines, and . The Inner ...
is the omphalos. In addition to the
Kun Lun Mountains The Kunlun Mountains ( zh, s=昆仑山, t=崑崙山, p=Kūnlún Shān, ; ug, كۇئېنلۇن تاغ تىزمىسى / قۇرۇم تاغ تىزمىسى ) constitute one of the longest mountain chains in Asia, extending for more than . In the bro ...
, where it is believed the peach tree of immortality is located, the
Chinese folk religion Chinese folk religion, also known as Chinese popular religion comprehends a range of traditional religious practices of Han Chinese, including the Chinese diaspora. Vivienne Wee described it as "an empty bowl, which can variously be filled ...
recognizes four other specific mountains as pillars of the world. Sacred places constitute world centers (
omphalos An omphalos is a religious stone artifact, or baetylus. In Ancient Greek, the word () means "navel". Among the Ancient Greeks, it was a widespread belief that Delphi was the center of the world. According to the myths regarding the founding of ...
) with the
altar An altar is a table or platform for the presentation of religious offerings, for sacrifices, or for other ritualistic purposes. Altars are found at shrines, temples, churches, and other places of worship. They are used particularly in pagan ...
or place of prayer as the axis. Altars, incense sticks, candles and torches form the axis by sending a column of smoke, and prayer, toward heaven. The architecture of sacred places often reflects this role. "Every temple or palace--and by extension, every sacred city or royal residence--is a Sacred Mountain, thus becoming a Centre."Mircea Eliade (tr. Willard Trask). 'Archetypes and Repetition' in ''The Myth of the Eternal Return. Princeton, 1971. p.12 The
stupa A stupa ( sa, स्तूप, lit=heap, ) is a mound-like or hemispherical structure containing relics (such as ''śarīra'' – typically the remains of Buddhist monks or nuns) that is used as a place of meditation. In Buddhism, circum ...
of
Hinduism Hinduism () is an Indian religion or '' dharma'', a religious and universal order or way of life by which followers abide. As a religion, it is the world's third-largest, with over 1.2–1.35 billion followers, or 15–16% of the global p ...
, and later
Buddhism Buddhism ( , ), also known as Buddha Dharma and Dharmavinaya (), is an Indian religion or philosophical tradition based on teachings attributed to the Buddha. It originated in northern India as a -movement in the 5th century BCE, and ...
, reflects
Mount Meru Mount Meru (Sanskrit/Pali: मेरु), also known as Sumeru, Sineru or Mahāmeru, is the sacred five-peaked mountain of Hindu, Jain, and Buddhist cosmology and is considered to be the centre of all the physical, metaphysical and spiritu ...
. Cathedrals are laid out in the form of a
cross A cross is a geometrical figure consisting of two intersecting lines or bars, usually perpendicular to each other. The lines usually run vertically and horizontally. A cross of oblique lines, in the shape of the Latin letter X, is termed a s ...
, with the vertical bar representing the union of Earth and heaven as the horizontal bars represent union of people to one another, with the altar at the intersection.
Pagoda A pagoda is an Asian tiered tower with multiple eaves common to Nepal, India, China, Japan, Korea, Myanmar, Vietnam, and other parts of Asia. Most pagodas were built to have a religious function, most often Buddhist but sometimes Taoist, ...
structures in Asian temples take the form of a stairway linking Earth and heaven. A
steeple In architecture, a steeple is a tall tower on a building, topped by a spire and often incorporating a belfry and other components. Steeples are very common on Christian churches and cathedrals and the use of the term generally connotes a religi ...
in a church or a
minaret A minaret (; ar, منارة, translit=manāra, or ar, مِئْذَنة, translit=miʾḏana, links=no; tr, minare; fa, گل‌دسته, translit=goldaste) is a type of tower typically built into or adjacent to mosques. Minarets are generall ...
in a mosque also serve as connections of Earth and heaven. Structures such as the
maypole A maypole is a tall wooden pole erected as a part of various European folk festivals, around which a maypole dance often takes place. The festivals may occur on 1 May or Pentecost (Whitsun), although in some countries it is instead erected at ...
, derived from the
Saxons The Saxons ( la, Saxones, german: Sachsen, ang, Seaxan, osx, Sahson, nds, Sassen, nl, Saksen) were a group of Germanic * * * * peoples whose name was given in the early Middle Ages to a large country (Old Saxony, la, Saxonia) near the Nor ...
'
Irminsul An Irminsul (Old Saxon 'great pillar') was a sacred, pillar-like object attested as playing an important role in the Germanic paganism of the Saxons. Medieval sources describe how an Irminsul was destroyed by Charlemagne during the Saxon Wars. ...
, and the
totem pole Totem poles ( hai, gyáaʼaang) are monumental carvings found in western Canada and the northwestern United States. They are a type of Northwest Coast art, consisting of poles, posts or pillars, carved with symbols or figures. They are usually ...
among
indigenous peoples of the Americas The Indigenous peoples of the Americas are the inhabitants of the Americas before the arrival of the European settlers in the 15th century, and the ethnic groups who now identify themselves with those peoples. Many Indigenous peoples of the A ...
also represent world axes. The calumet, or sacred pipe, represents a column of smoke (the soul) rising form a world center. A
mandala A mandala ( sa, मण्डल, maṇḍala, circle, ) is a geometric configuration of symbols. In various spiritual traditions, mandalas may be employed for focusing attention of practitioners and adepts, as a spiritual guidance tool, for e ...
creates a world center within the boundaries of its two-dimensional space analogous to that created in three-dimensional space by a shrine. In medieval times some Christians thought of
Jerusalem Jerusalem (; he, יְרוּשָׁלַיִם ; ar, القُدس ) (combining the Biblical and common usage Arabic names); grc, Ἱερουσαλήμ/Ἰεροσόλυμα, Hierousalḗm/Hierosóluma; hy, Երուսաղեմ, Erusałēm. i ...
as the center of the world (Latin: ''umbilicus mundi'', Greek: ''Omphalos''), and was so represented in the so-called
T and O map A T and O map or O–T or T–O map (''orbis terrarum'', orb or circle of the lands; with the letter T inside an O), also known as an Isidoran map, is a type of early world map that represents the physical world as first described by the 7th-ce ...
s. Byzantine hymns speak of the Cross being "planted in the center of the earth."


Center of a flat Earth

The
Flat Earth The flat-Earth model is an archaic and scientifically disproven conception of Earth's shape as a plane or disk. Many ancient cultures subscribed to a flat-Earth cosmography, including Greece until the classical period (5th century BC), t ...
model is a belief that the
Earth Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's sur ...
's shape is a plane or disk covered by a
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 ...
containing heavenly bodies. Most pre-scientific cultures have had conceptions of a Flat Earth, including
Greece Greece,, or , romanized: ', officially the Hellenic Republic, is a country in Southeast Europe. It is situated on the southern tip of the Balkans, and is located at the crossroads of Europe, Asia, and Africa. Greece shares land borders wi ...
until the classical period, the
Bronze Age The Bronze Age is a historic period, lasting approximately from 3300 BC to 1200 BC, characterized by the use of bronze, the presence of writing in some areas, and other early features of urban civilization. The Bronze Age is the second pri ...
and
Iron Age The Iron Age is the final epoch of the three-age division of the prehistory and protohistory of humanity. It was preceded by the Stone Age ( Paleolithic, Mesolithic, Neolithic) and the Bronze Age ( Chalcolithic). The concept has been mostly ...
civilizations of the
Near East The ''Near East''; he, המזרח הקרוב; arc, ܕܢܚܐ ܩܪܒ; fa, خاور نزدیک, Xāvar-e nazdik; tr, Yakın Doğu is a geographical term which roughly encompasses a transcontinental region in Western Asia, that was once the hist ...
until the
Hellenistic period In Classical antiquity, the Hellenistic period covers the time in Mediterranean history after Classical Greece, between the death of Alexander the Great in 323 BC and the emergence of the Roman Empire, as signified by the Battle of Actium in ...
,
India India, officially the Republic of India (Hindi: ), is a country in South Asia. It is the List of countries and dependencies by area, seventh-largest country by area, the List of countries and dependencies by population, second-most populous ...
until the
Gupta period The Gupta Empire was an ancient Indian empire which existed from the early 4th century CE to late 6th century CE. At its zenith, from approximately 319 to 467 CE, it covered much of the Indian subcontinent. This period is considered as the Gold ...
(early centuries AD) and
China China, officially the People's Republic of China (PRC), is a country in East Asia. It is the world's List of countries and dependencies by population, most populous country, with a Population of China, population exceeding 1.4 billion, slig ...
until the 17th century. It was also typically held in the aboriginal cultures of the
Americas The Americas, which are sometimes collectively called America, are a landmass comprising the totality of North America, North and South America. The Americas make up most of the land in Earth's Western Hemisphere and comprise the New World. ...
, and a flat Earth domed by 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 ...
in the shape of an inverted bowl is common in pre-scientific societies. "Center" is well-defined in a Flat Earth model. A flat Earth would have a definite geographic center. There would also be a unique point at the exact center of a spherical
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 ...
(or a firmament that was a half-sphere).


Earth as the center of the Universe

The Flat Earth model gave way to an understanding of a
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. ...
.
Aristotle Aristotle (; grc-gre, Ἀριστοτέλης ''Aristotélēs'', ; 384–322 BC) was a Greek philosopher and polymath during the Classical period in Ancient Greece. Taught by Plato, he was the founder of the Peripatetic school of ...
(384–322 BC) provided observational arguments supporting the idea of a spherical Earth, namely that different stars are visible in different locations, travelers going south see southern constellations rise higher above the horizon, and the shadow of Earth on the Moon during a
lunar eclipse A lunar eclipse occurs when the Moon moves into the Earth's shadow. Such alignment occurs during an eclipse season, approximately every six months, during the full moon phase, when the Moon's orbital plane is closest to the plane of the Ear ...
is round, and spheres cast circular shadows while discs generally do not. This understanding was accompanied by models of the Universe that depicted the
Sun The Sun is the star at the center of the Solar System. It is a nearly perfect ball of hot plasma, heated to incandescence by nuclear fusion reactions in its core. The Sun radiates this energy mainly as light, ultraviolet, and infrared radi ...
,
Moon The Moon is Earth's only natural satellite. It is the fifth largest satellite in the Solar System and the largest and most massive relative to its parent planet, with a diameter about one-quarter that of Earth (comparable to the width of ...
,
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, and naked eye planets circling the spherical Earth, including the noteworthy models of
Aristotle Aristotle (; grc-gre, Ἀριστοτέλης ''Aristotélēs'', ; 384–322 BC) was a Greek philosopher and polymath during the Classical period in Ancient Greece. Taught by Plato, he was the founder of the Peripatetic school of ...
(see
Aristotelian physics Aristotelian physics is the form of natural science described in the works of the Greek philosopher Aristotle (384–322 BC). In his work ''Physics'', Aristotle intended to establish general principles of change that govern all natural bodies, b ...
) and
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 ...
. This
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 ...
was the dominant model from the 4th century BC until the 17th century AD.


Sun as center of the Universe

Heliocentrism, or heliocentricism,Copernican heliocenterism held that the Sun itself was the center of the entire Universe. As it is modernly understood, Heliocenterism refers to the much narrower concept that the Sun is the center of the Solar System, not the center of the entire Universe. is the
astronomical Astronomy () is a natural science that studies celestial objects and phenomena. It uses mathematics, physics, and chemistry in order to explain their origin and evolution. Objects of interest include planets, moons, stars, nebulae, galaxi ...
model in which the Earth and planets revolve around a relatively stationary Sun at the center of the
Solar System The Solar System Capitalization of the name varies. The International Astronomical Union, the authoritative body regarding astronomical nomenclature, specifies capitalizing the names of all individual astronomical objects but uses mixed "Solar ...
. The word comes from the
Greek Greek may refer to: Greece Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group. *Greek language, a branch of the Indo-European language family. **Proto-Greek language, the assumed last common ancestor ...
( ''
helios In ancient Greek religion and mythology, Helios (; grc, , , Sun; Homeric Greek: ) is the god and personification of the Sun (Solar deity). His name is also Latinized as Helius, and he is often given the epithets Hyperion ("the one above") an ...
'' "sun" and ''kentron'' "center"). The notion that the Earth revolves around the Sun had been proposed as early as the 3rd century BC by
Aristarchus of Samos Aristarchus of Samos (; grc-gre, Ἀρίσταρχος ὁ Σάμιος, ''Aristarkhos ho Samios''; ) was an ancient Greek astronomer and mathematician who presented the first known heliocentric model that placed the Sun at the center of the ...
,The work of Aristarchus's in which he proposed his heliocentric system has not survived. We only know of it now from a brief passage in
Archimedes Archimedes of Syracuse (;; ) was a Greek mathematician, physicist, engineer, astronomer, and inventor from the ancient city of Syracuse in Sicily. Although few details of his life are known, he is regarded as one of the leading scientis ...
's ''
The Sand Reckoner ''The Sand Reckoner'' ( el, Ψαμμίτης, ''Psammites'') is a work by Archimedes, an Ancient Greek mathematician of the 3rd century BC, in which he set out to determine an upper bound for the number of grains of sand that fit into the unive ...
''.
but had received no support from most other ancient astronomers.
Nicolaus 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 ...
' major theory of a heliocentric model was published in ''
De revolutionibus orbium coelestium ''De revolutionibus orbium coelestium'' (English translation: ''On the Revolutions of the Heavenly Spheres'') is the seminal work on the heliocentric theory of the astronomer Nicolaus Copernicus (1473–1543) of the Polish Renaissance. The book, ...
'' (''On the Revolutions of the Celestial Spheres''), in 1543, the year of his death, though he had formulated the theory several decades earlier. Copernicus' ideas were not immediately accepted, but they did begin a paradigm shift away from the Ptolemaic geocentric model to a heliocentric model. The
Copernican revolution The Copernican Revolution was the paradigm shift from the Ptolemaic model of the heavens, which described the cosmos as having Earth stationary at the center of the universe, to the heliocentric model with the Sun at the center of the Solar Syst ...
, as this paradigm shift would come to be called, would last until
Isaac Newton Sir Isaac Newton (25 December 1642 – 20 March 1726/27) was an English mathematician, physicist, astronomer, alchemist, Theology, theologian, and author (described in his time as a "natural philosophy, natural philosopher"), widely ...
’s work over a century later.
Johannes 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 ...
published his first two laws about planetary motion in 1609, having found them by analyzing the astronomical observations of
Tycho Brahe Tycho Brahe ( ; born Tyge Ottesen Brahe; generally called Tycho (14 December 154624 October 1601) was a Danish astronomer, known for his comprehensive astronomical observations, generally considered to be the most accurate of his time. He was ...
. Kepler's third law was published in 1619. The first law was "The
orbit In celestial mechanics, an orbit is the curved trajectory of an object such as the trajectory of a planet around a star, or of a natural satellite around a planet, or of an artificial satellite around an object or position in space such as ...
of every
planet A planet is a large, rounded astronomical body that is neither a star nor its remnant. The best available theory of planet formation is the nebular hypothesis, which posits that an interstellar cloud collapses out of a nebula to create a you ...
is an
ellipse In mathematics, an ellipse is a plane curve surrounding two focal points, such that for all points on the curve, the sum of the two distances to the focal points is a constant. It generalizes a circle, which is the special type of ellipse in ...
with the Sun at one of the two foci." On 7 January 1610 Galileo used his telescope, with optics superior to what had been available before. He described "three fixed stars, totally invisible''i.e.'', invisible to the naked eye. by their smallness", all close to Jupiter, and lying on a straight line through it. Observations on subsequent nights showed that the positions of these "stars" relative to Jupiter were changing in a way that would have been inexplicable if they had really been fixed stars. On 10 January Galileo noted that one of them had disappeared, an observation which he attributed to its being hidden behind Jupiter. Within a few days he concluded that they were
orbit In celestial mechanics, an orbit is the curved trajectory of an object such as the trajectory of a planet around a star, or of a natural satellite around a planet, or of an artificial satellite around an object or position in space such as ...
ing Jupiter:In ''Sidereus Nuncius'
1892, 3:81
Galileo stated that he had reached this conclusion on 11 January. He had discovered three of Jupiter's four largest
satellites A satellite or artificial satellite is an object intentionally placed into orbit in outer space. Except for passive satellites, most satellites have an electricity generation system for equipment on board, such as solar panels or radioisotop ...
(moons). He discovered the fourth on 13 January. His observations of the satellites of Jupiter created a revolution in astronomy: a planet with smaller planets orbiting it did not conform to the principles of Aristotelian Cosmology, which held that all heavenly bodies should circle the Earth. Many astronomers and philosophers initially refused to believe that Galileo could have discovered such a thing;  by showing that, like Earth, other planets could also have moons of their own that followed prescribed paths, and hence that
orbital mechanics Orbital mechanics or astrodynamics is the application of ballistics and celestial mechanics to the practical problems concerning the motion of rockets and other spacecraft. The motion of these objects is usually calculated from Newton's laws of ...
didn't apply only to the Earth, planets, and Sun, what Galileo had essentially done was to show that other planets might be "like Earth". Newton made clear his
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 ...
view of the Solar System – developed in a somewhat modern way, because already in the mid-1680s he recognised the "deviation of the Sun" from the centre of gravity of the solar system. For Newton, it was not precisely the centre of the Sun or any other body that could be considered at rest, but rather "the common centre of gravity of the Earth, the Sun and all the Planets is to be esteem'd the Centre of the World", and this centre of gravity "either is at rest or moves uniformly forward in a right line" (Newton adopted the "at rest" alternative in view of common consent that the centre, wherever it was, was at rest).


Milky Way's Galactic Center as center of the Universe

Before the 1920s, it was generally believed that there were no galaxies other than the Milky Way (see for example The Great Debate). Thus, to astronomers of previous centuries, there was no distinction between a hypothetical center of the galaxy and a hypothetical center of the universe. In 1750 Thomas Wright, in his work ''An original theory or new hypothesis of the Universe'', correctly speculated that the
Milky Way The Milky Way is the galaxy that includes our Solar System, with the name describing the galaxy's appearance from Earth: a hazy band of light seen in the night sky formed from stars that cannot be individually distinguished by the naked eye. ...
might be a body of a huge number of stars held together by gravitational forces rotating about a
Galactic Center The Galactic Center or Galactic Centre is the rotational center, the barycenter, of the Milky Way galaxy. Its central massive object is a supermassive black hole of about 4 million solar masses, which is called Sagittarius A*, a compact ra ...
, akin to the Solar System but on a much larger scale. The resulting disk of stars can be seen as a band on the sky from the Earth's perspective inside the disk. In a treatise in 1755,
Immanuel Kant Immanuel Kant (, , ; 22 April 1724 – 12 February 1804) was a German philosopher and one of the central Enlightenment thinkers. Born in Königsberg, Kant's comprehensive and systematic works in epistemology, metaphysics, ethics, and ...
elaborated on Wright's idea about the structure of the Milky Way. In 1785,
William Herschel Frederick William Herschel (; german: Friedrich Wilhelm Herschel; 15 November 1738 – 25 August 1822) was a German-born British astronomer and composer. He frequently collaborated with his younger sister and fellow astronomer Caroline ...
proposed such a model based on observation and measurement, leading to scientific acceptance of galactocentrism, a form of
heliocentrism 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 ...
with the
Sun The Sun is the star at the center of the Solar System. It is a nearly perfect ball of hot plasma, heated to incandescence by nuclear fusion reactions in its core. The Sun radiates this energy mainly as light, ultraviolet, and infrared radi ...
at the center of the Milky Way. The 19th century astronomer Johann Heinrich von Mädler proposed the Central Sun Hypothesis, according to which the stars of the universe revolved around a point in the
Pleiades The Pleiades (), also known as The Seven Sisters, Messier 45 and other names by different cultures, is an asterism and an open star cluster containing middle-aged, hot B-type stars in the north-west of the constellation Taurus. At a distance ...
.


The nonexistence of a center of the Universe

In 1917,
Heber Doust Curtis Heber Doust Curtis (June 27, 1872 – January 9, 1942) was an American astronomer. He participated in 11 expeditions for the study of solar eclipses, and, as an advocate and theorist that additional galaxies existed outside of the Milky Way, wa ...
observed a
nova A nova (plural novae or novas) is a transient astronomical event that causes the sudden appearance of a bright, apparently "new" star (hence the name "nova", which is Latin for "new") that slowly fades over weeks or months. Causes of the dramat ...
within what then was called the " Andromeda Nebula". Searching the photographic record, 11 more novae were discovered. Curtis noticed that novas in Andromeda were drastically fainter than novas in the
Milky Way The Milky Way is the galaxy that includes our Solar System, with the name describing the galaxy's appearance from Earth: a hazy band of light seen in the night sky formed from stars that cannot be individually distinguished by the naked eye. ...
. Based on this, Curtis was able to estimate that Andromeda was 500,000
light-year A light-year, alternatively spelled light year, is a large unit of length used to express astronomical distance, astronomical distances and is equivalent to about 9.46 Orders of magnitude (numbers)#1012, trillion kilometers (), or 5.88  ...
s away. As a result, Curtis became a proponent of the so-called "island Universes" hypothesis, which held that objects previously believed to be
spiral nebulae Spiral galaxies form a class of galaxy originally described by Edwin Hubble in his 1936 work ''The Realm of the Nebulae''the Great Debate between
Harlow Shapley Harlow Shapley (November 2, 1885 – October 20, 1972) was an American scientist, head of the Harvard College Observatory (1921–1952), and political activist during the latter New Deal and Fair Deal. Shapley used Cepheid variable stars to estim ...
and Curtis took place, concerning the nature of the Milky Way, spiral nebulae, and the dimensions of the Universe. To support his claim that the Great Andromeda Nebula (M31) was an external galaxy, Curtis also noted the appearance of dark lanes resembling the dust clouds in this galaxy, as well as the significant
Doppler shift The Doppler effect or Doppler shift (or simply Doppler, when in context) is the change in frequency of a wave in relation to an observer who is moving relative to the wave source. It is named after the Austrian physicist Christian Doppler, who ...
. In 1922
Ernst Öpik Ernst Julius Öpik ( – 10 September 1985) was an Estonian astronomer and astrophysicist who spent the second half of his career (1948–1981) at the Armagh Observatory in Northern Ireland. Education Öpik was born in Kunda, Lääne-Viru, Go ...
presented an elegant and simple astrophysical method to estimate the distance of M31. His result put the Andromeda Nebula far outside this galaxy at a distance of about 450,000
parsec The parsec (symbol: pc) is a unit of length used to measure the large distances to astronomical objects outside the Solar System, approximately equal to or (au), i.e. . The parsec unit is obtained by the use of parallax and trigonometry, an ...
, which is about 1,500,000 ly.
Edwin Hubble Edwin Powell Hubble (November 20, 1889 – September 28, 1953) was an American astronomer. He played a crucial role in establishing the fields of extragalactic astronomy and observational cosmology. Hubble proved that many objects previousl ...
settled the debate about whether other galaxies exist in 1925 when he identified extragalactic Cepheid variable stars for the first time on astronomical photos of M31. These were made using the 2.5 metre (100 in)
Hooker telescope The Mount Wilson Observatory (MWO) is an astronomical observatory in Los Angeles County, California, United States. The MWO is located on Mount Wilson, a peak in the San Gabriel Mountains near Pasadena, northeast of Los Angeles. The observato ...
, and they enabled the distance of Great Andromeda Nebula to be determined. His measurement demonstrated conclusively that this feature was not a cluster of stars and gas within this galaxy, but an entirely separate galaxy located a significant distance from the Milky Way. This proved the existence of other galaxies.


Expanding Universe

Hubble also demonstrated that the
redshift In physics, a redshift is an increase in the wavelength, and corresponding decrease in the frequency and photon energy, of electromagnetic radiation (such as light). The opposite change, a decrease in wavelength and simultaneous increase in fr ...
of other galaxies is approximately proportional to their distance from Earth (
Hubble's law Hubble's law, also known as the Hubble–Lemaître law, is the observation in physical cosmology that galaxies are moving away from Earth at speeds proportional to their distance. In other words, the farther they are, the faster they are moving a ...
). This raised the appearance of this galaxy being in the center of an expanding Universe, however, Hubble rejected the findings philosophically: The redshift observations of Hubble, in which galaxies appear to be moving away from us at a rate proportional to their distance from us, are now understood to be a result of the
metric expansion of space The expansion of the universe is the increase in distance between any two given gravitationally unbound parts of the observable universe with time. It is an intrinsic expansion whereby the scale of space itself changes. The universe does not ex ...
. This is the increase of the distance between two distant parts of the Universe with time, and is an intrinsic expansion whereby the scale of space itself changes. As Hubble theorized, all observers anywhere in the Universe will observe a similar effect.


Copernican and cosmological principles

The
Copernican principle In physical cosmology, the Copernican principle states that humans, on the Earth or in the Solar System, are not privileged observers of the universe, that observations from the Earth are representative of observations from the average position ...
, named after Nicolaus Copernicus, states that the Earth is not in a central, specially favored position.
Hermann Bondi Sir Hermann Bondi (1 November 1919 – 10 September 2005) was an Austrian- British mathematician and cosmologist. He is best known for developing the steady state model of the universe with Fred Hoyle and Thomas Gold as an alternative to the ...
named the principle after Copernicus in the mid-20th century, although the principle itself dates back to the 16th-17th century
paradigm shift A paradigm shift, a concept brought into the common lexicon by the American physicist and philosopher Thomas Kuhn, is a fundamental change in the basic concepts and experimental practices of a scientific discipline. Even though Kuhn restricted ...
away from the geocentric
Ptolemaic system 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 ...
. The
cosmological principle In modern physical cosmology, the cosmological principle is the notion that the spatial distribution of matter in the universe is homogeneous and isotropic when viewed on a large enough scale, since the forces are expected to act uniformly throu ...
is an extension of the Copernican principle which states that the Universe is homogeneous (the same observational evidence is available to observers at different locations in the Universe) and isotropic (the same observational evidence is available by looking in any direction in the Universe). A homogeneous, isotropic Universe does not have a center.


See also

*
Center of the universe (disambiguation) The center of the universe may refer to: Astronomy *Geocentric model, the astronomical model which places Earth at the orbital center of all celestial bodies *Heliocentrism, the astronomical model in which the Sun is at the orbital center of the ...
*
Cosmic microwave background In Big Bang cosmology the cosmic microwave background (CMB, CMBR) is electromagnetic radiation that is a remnant from an early stage of the universe, also known as "relic radiation". The CMB is faint cosmic background radiation filling all spac ...
*
Earth's inner core Earth's inner core is the innermost geologic layer of planet Earth. It is primarily a solid ball with a radius of about , which is about 20% of Earth's radius or 70% of the Moon's radius. There are no samples of Earth's core accessible for d ...
*
Galactic Center The Galactic Center or Galactic Centre is the rotational center, the barycenter, of the Milky Way galaxy. Its central massive object is a supermassive black hole of about 4 million solar masses, which is called Sagittarius A*, a compact ra ...
*
Geographical centre of Earth The geographical center of Earth is the geometric center of all land surfaces on Earth. Geometrically defined it is the Centroid of all land surfaces within the two dimensions of the Geoid surface which approximates the Earth's outer shape. The ...
*
Great Attractor The Great Attractor is a gravitational anomaly in intergalactic space and the apparent central gravitational point of the Laniakea Supercluster. The observed anomalies suggest a localized concentration of mass millions of times more massive than ...
* Illustris project * List of places referred to as the Center of the Universe *
Multiverse The multiverse is a hypothetical group of multiple universes. Together, these universes comprise everything that exists: the entirety of space, time, matter, energy, information, and the physical laws and constants that describe them. The dif ...
*
Religious cosmology Religious cosmology is an explanation of the origin, evolution, and eventual fate of the universe from a religious perspective. This may include beliefs on origin in the form of a creation myth, subsequent evolution, current organizational form ...
*
Sun The Sun is the star at the center of the Solar System. It is a nearly perfect ball of hot plasma, heated to incandescence by nuclear fusion reactions in its core. The Sun radiates this energy mainly as light, ultraviolet, and infrared radi ...
– the center of the
Solar System The Solar System Capitalization of the name varies. The International Astronomical Union, the authoritative body regarding astronomical nomenclature, specifies capitalizing the names of all individual astronomical objects but uses mixed "Solar ...
* Three-torus model of the universe


Notes


References

{{Portal bar, History, Religion, Stars, Solar System, Science Center of the Universe Physical cosmology Obsolete scientific theories