Earth's location in the universe
Knowledge of Earth's location in the universe has been shaped by 400 years of telescopic observations, and has expanded radically in the last century. Initially, Earth was believed to be the center of the universe, which consisted only of those planets visible with the naked eye and an outlying sphere of fixed stars. After the acceptance of the heliocentric model in the 17th century, observations by William Herschel and others showed that the Sun lay within a vast, disc-shaped galaxy of stars. By the 20th century, observations of spiral nebulae revealed that our galaxy was one of billions in an expanding universe, grouped into clusters and superclusters. By the 21st century, the overall structure of the visible universe was becoming clearer, with superclusters forming into a vast web of filaments and voids. Superclusters, filaments and voids are likely the largest coherent structures that exist in the Universe. At still larger scales (over 1000 megaparsecs)[e] the Universe becomes homogeneous meaning that all its parts have on average the same density, composition and structure.
Since there is believed to be no "center" or "edge" of the universe, there is no particular reference point with which to plot the overall location of the Earth in the universe. The Earth is at the center of the observable universe because its observability is determined by its distance from Earth. Reference can be made to the Earth's position with respect to specific structures, which exist at various scales. It is still undetermined whether the universe is infinite.
|Earth in the Universe|
|Earth||12,700 km in diameter||Residence of humanity.||
|Geospace||63,000 km Sunward side;
6,300,000 km trailing side
|The space dominated by Earth's magnetic field.||
|Orbit of the Moon||770,000 km across||The average diameter of the orbit of the Moon relative to the Earth.||
|Earth's orbit||300 million km across
2 AU across [a]
|The average diameter of the orbit of the Earth relative to the Sun.
Contains the Sun, Mercury and Venus.
|Inner Solar System||6 AU across||Contains the Sun, the inner planets (Mercury, Venus, Earth, Mars) and the asteroid belt.||
|Outer Solar System||60 AU across||Surrounds the inner Solar System; comprises the outer planets (Jupiter, Saturn, Uranus, Neptune).||
|Kuiper belt||96 AU across||Belt of icy objects surrounding the outer solar system. Contains the dwarf planets Pluto, Haumea and Makemake.||
|Heliosphere||160 AU across||Maximum extent of the solar wind and the interplanetary medium.||
|Scattered disk||200 AU across||Region of sparsely scattered icy objects surrounding the Kuiper belt. Contains the dwarf planet Eris.||
|Oort cloud[b]||100,000–200,000 AU across
|Spherical shell of over a trillion comets.||
|Solar System||4 light-years across||The Sun and its planetary system. At this point, the Sun's gravity gives way to that of surrounding stars.||
|Local Interstellar Cloud||30 light-years across||Interstellar cloud of gas through which the Sun and a number of other stars are currently travelling.[d]||
|Local Bubble||210–815 light-years across||Cavity in the interstellar medium in which the Sun and a number of other stars are currently travelling.[d]
Caused by a past supernova.
|Gould Belt||3,000 light-years across||Ring of young stars through which the Sun is currently travelling.[d]||
|Orion Arm||10,000 light-years in length||The spiral arm of the Milky Way Galaxy through which the Sun is currently travelling.[d]
|Orbit of the Solar System||56,000 light years across||The average diameter of the orbit of the Solar System relative to the Galactic Center. The Sun's orbital radius is roughly 28,000 light years, or slightly over half way to the galactic edge. One orbital period of the Solar System lasts between 225 and 250 million years.||
|Milky Way Galaxy||100,000 light-years across||Our home galaxy, composed of 200 billion to 400 billion stars and filled with the interstellar medium.||
|Milky Way subgroup||2.74 million light-years across,
|The Milky Way and those satellite galaxies gravitationally bound to it, such as the Sagittarius Dwarf, the Ursa Minor Dwarf and the Canis Major Dwarf. Cited distance is the orbital diameter of the Leo T Dwarf galaxy, the most distant galaxy in the Milky Way subgroup.||
|Local Group||3 megaparsecs across||Group of at least 47 galaxies. Dominated by Andromeda (the largest), the Milky Way and Triangulum; the remainder are dwarf galaxies.||
|Local Sheet||7 megaparsecs across||Group of galaxies including the Local Group moving at the same relative velocity towards the Virgo Cluster and away from the Local Void.||
|Virgo Supercluster||33 megaparsecs across||The supercluster of which our Local Group is a part; comprises roughly 100 galaxy groups and clusters, centred on the Virgo Cluster.||
|Laniakea||160 megaparsecs across||A group connected with the superclusters of which our Local Group is a part; comprises roughly 300 to 500 galaxy groups and clusters, centred on the Great Attractor in the Hydra-Centaurus Supercluster.|
|Observable universe||28,000 megaparsecs across||The large-scale structure of the universe consists of more than 100 billion galaxies, arranged in millions of superclusters, galactic filaments, and voids, creating a foam-like superstructure.||
|Universe||Minimum of 28,000 megaparsecs||Beyond the observable universe lie the unobservable regions from which no light has reached the Earth yet. No information is available, as light is the fastest travelling medium of information. However, since there is no reason to suppose different natural laws, the universe is likely to contain more galaxies in the same foam-like superstructure.|
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