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Historically, the center of the Universe had been believed to be a number of locations. Many mythological cosmologies included an axis mundi, the central axis of a flat Earth that connects the Earth, heavens, and other realms together. In the 4th century BCE Greece, the geocentric model was developed based on astronomical observation, proposing 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 model by Nicolaus Copernicus in the 16th century, the sun was believed to be the center of the Universe, with the planets (including Earth) and stars orbiting around it.
In the early 20th century, the discovery of other galaxies and the development of the Big Bang theory led to the development of cosmological models of a homogeneous, isotropic Universe (which lacks a central point) that is expanding at all points.
In religion or mythology, the axis mundi (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 was regarded as the axis mundi in Caananite tradition, from where the sons of God are introduced descending in 1 Enoch (1En6:6). The ancient Greeks regarded several sites as places of earth's omphalos (navel) stone, notably the oracle at Delphi, while still maintaining a belief in a cosmic world tree and in Mount Olympus as the abode of the gods. Judaism has the Temple Mount and Mount Sinai, Christianity has the Mount of Olives and Calvary, Islam has Mecca, said to be the place on earth that was created first, and the Temple Mount (Dome of the Rock). In Shinto, the Ise Shrine is the omphalos. In addition to the Kun Lun Mountains, where it is believed the peach tree of immortality is located, the Chinese folk religion recognizes four other specific mountains as pillars of the world.
Sacred places constitute world centers (omphalos) with the altar 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." The stupa of Hinduism, and later Buddhism, reflects Mount Meru. Cathedrals are laid out in the form of a cross, 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 structures in Asian temples take the form of a stairway linking earth and heaven. A steeple in a church or a minaret in a mosque also serve as connections of earth and heaven. Structures such as the maypole, derived from the Saxons' Irminsul, and the totem pole among indigenous peoples of the Americas also represent world axes. The calumet, or sacred pipe, represents a column of smoke (the soul) rising form a world center. A mandala 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 as the center of the world (Latin: umbilicus mundi, Greek: Omphalos), and was so represented in the so-called T and O maps. Byzantine hymns speak of the Cross being "planted in the center of the earth.
"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 (or a firmament that was a half-sphere).
The Flat Earth model gave way to an understanding of the Spherical Earth. Aristotle (384–322 BCE) 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 is round, and spheres cast circular shadows while discs generally do not.
Eratosthenes (276–194 BCE) estimated the spherical Earth's circumference by measuring the different angles cast by shadows in different locations. He had heard that in Syene the sun was directly overhead at the summer solstice whereas in Alexandria the sun cast a shadow. Using the angles the shadows made as the basis of his trigonometric calculations, Eratosthenes obtained a relatively accurate estimated the size of the Spherical Earth.
In astronomy, the geocentric model (also known as geocentrism or the Ptolemaic system), is the superseded theory that the Earth is the center of the universe, and that all other objects orbit around it. This geocentric model served as the predominant cosmological system in many ancient civilizations such as ancient Greece. As such, most Ancient Greek philosophers assumed that the Sun, Moon, stars, and naked eye planets circled the Earth, including the noteworthy systems of Aristotle (see Aristotelian physics) and Ptolemy.
On 7 January 1610 Galileo observed with his telescope what he described at the time as "three fixed stars, totally invisible 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 orbiting Jupiter: He had discovered three of Jupiter's four largest satellites (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, and many astronomers and philosophers initially refused to believe that Galileo could have discovered such a thing.
Heliocentrism, or heliocentricism, is the astronomical model in which the Earth and planets revolve around a relatively stationary Sun at the center of our Solar System. The word comes from the Greek (ἥλιος helios "sun" and κέντρον kentron "center"). Historically, heliocentrism was opposed to geocentrism, which placed the Earth at the center. The notion that the Earth revolves around the Sun had been proposed as early as the 3rd century BC by Aristarchus of Samos, but had received no support from most other ancient astronomers.
Archaic theories of 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.
Newton made clear his heliocentric 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).
In 1750 Thomas Wright, in his work An original theory or new hypothesis of the Universe, correctly speculated that the Milky Way might be a rotating body of a huge number of stars held together by gravitational forces, 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 our perspective inside the disk. In a treatise in 1755, Immanuel Kant elaborated on Wright's idea about the structure of the Milky Way.
In 1917, Heber Doust Curtis observed a nova within 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. Based on this, Curtis was able to estimate that Andromeda was 500,000 light-years away. As a result, Curtis became a proponent of the so-called "island universes" hypothesis, which held that spiral nebulae were actually independent galaxies.
In 1920, the Great Debate between Harlow Shapley 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 our own Galaxy, as well as the significant Doppler shift. In 1922 Ernst Öpik presented a very elegant and simple astrophysical method to estimate the distance of M31. His result put the Andromeda Nebula far outside our Galaxy at a distance of about 450,000 parsec, which is about 1,500,000 ly. Edwin Hubble settled the debate 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, 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 our Galaxy, but an entirely separate galaxy located a significant distance from our own.
The Copernican principle, named after Nicolaus Copernicus, states that the Earth is not in a central, specially favored position. Hermann Bondi named the principle after Copernicus in the mid-20th century, although the principle itself dates back to the 16th-17th century paradigm shift away from the Ptolemaic system, which placed Earth at the center of the Universe.
The cosmological principle 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.
The "intergalactic starship" is a thought experiment that is used to explain the concept of "shape of the universe". (It is not actually believed to be possible under modern understandings of physics.)[clarification needed]
Supposed an immortal observer left Earth and traveled off into space, traveling continuously in a perfectly straight line. There are two main possibilities for what that observer might experience: The observer could experience an infinitely-novel voyage, never seeing the same place twice, or the observer could, despite traveling in a straight line, eventually return to a place that they had previously visited.
By analogy, consider a person on the surface the earth trying to decide between a flat earth and a spherical earth. In the flat earth model, if they travel indefinitely in a straight line, they would never retrace their steps. In a spherical earth model, a person traveling in a "straight" line would eventually return to a place they have visited before.
If the imaginary "intergalactic starship" could travel forever in a straight line without visiting the same place twice, that would be consistent with a universe that is infinitely large, perfectly flat, and homogenous. In an infinitely large universe, there is no "center point", just as there is no "center number" between 1 and infinity. In a perfectly flat universe, parallel 'straight lines' never intersect, so there would be no single point that could be called a geometric center. In a homogenous universe, matter is distributed roughly uniformly through all parts of the universe. In such a universe, there is no center of mass.