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 Earth's Sun lay within a vast, disc-shaped galaxy of stars, later revealed to be suns like our own. By the 20th century, observations of spiral nebulae revealed that our galaxy was only 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.[1]

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.[2] 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, and there is speculation that our universe might only be one of countless trillions within a larger multiverse, itself contained within the omniverse.

A diagram of our location in the observable Universe. (Click here for larger image.)
Earth in the Universe
Feature Size Notes Sources
Earth 12,700 km in diameter Our planet.
[3]
Geospace 63,000 km Sunward side;
6,300,000 km trailing side		 The space dominated by Earth's magnetic field.
[4]
Orbit of the Moon 770,000 km across The average diameter of the orbit of the Moon relative to the Earth.
[5]
Earth's orbit 300 million km across
2 AU[a]		 The average diameter of the orbit of the Earth relative to the Sun.
Contains the Sun, Mercury and Venus.
[6]
Inner Solar System 6 AU across Contains the Sun, the inner planets (Mercury, Venus, Earth, Mars) and the asteroid belt.
[7]
Outer Solar System 60 AU across Surrounds the inner Solar System; comprises the outer planets (Jupiter, Saturn, Uranus, Neptune).
[8]
Kuiper belt 96 AU across Belt of icy objects surrounding the outer solar system. Contains the dwarf planets Pluto, Haumea and Makemake.
[9]
Heliosphere 160 AU across Maximum extent of the Solar wind and the interplanetary medium.
[10][11]
Scattered disk 200 AU across Region of sparsely scattered icy objects surrounding the Kuiper belt. Contains the dwarf planet Eris.
[12]
Oort cloud[b] 100,000-200,000 AU across
2-4 light-years[c]		 Spherical shell of over a trillion comets.
[13]
Solar System 4 light-years across Our home planetary system. At this point, the Sun's gravity gives way to that of surrounding stars.
[14]
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]
[15]
Local Bubble 210-815 light-years across Cavity in the interstellar medium in which our Sun and a number of other stars are currently travelling.[d]
Caused by a past supernova.
[16][17]
Gould Belt 3,000 light-years across Ring of young stars through which our Sun is currently travelling.[d]
[18]
Orion Arm 10,000 light-years in length The spiral arm of the Milky Way Galaxy through which our Sun is currently travelling.[d]
[19]
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. Our Sun's orbital radius is roughly 28,000 light years, or slightly over half way to the galactic edge. One orbital period of our Solar System lasts between 225 and 250 million years.
[20][21]
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.
[22][23]
Milky Way subgroup 1.64 million light-years across
0.5 megaparsecs[e]		 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 I Dwarf galaxy, the most distant galaxy in the Milky Way subgroup.
[24][25]
Local Group 3 megaparsecs across Group of at least 47 galaxies. Dominated by Andromeda (the largest), The Milky Way and Triangulum; the remainder are small dwarf galaxies.
[26]
Virgo Supercluster 33 megaparsecs across The supercluster of which our Local Group is a part; comprises roughly 100 galaxy groups and clusters.
[27][28]
Pisces-Cetus Supercluster Complex 300 megaparsecs across The galaxy filament of which the Virgo Supercluster is a part.
[29]
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.
[30][31]
Universe Minimum of 28,000 megaparsecs Beyond the observable universe lies the unobservable regions where no light from those regions has reached the Earth yet. No information is available about the region, 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.
a 1 AU or astronomical unit is the distance between the Earth and the Sun, or 150 million km. Earth's orbital diameter is twice its orbital radius, or 2 AU.
b Existence is hypothetical.
c One light-year is the distance light travels in a year; equivalent to ~9.5 trillion km or 63,240 AU
d The Sun is not gravitationally tied to any larger structures within the Galaxy.[32] These regions simply mark its current location in its orbit around the Galactic center.
e One megaparsec is equivalent to one million parsecs or 3.26 million light-years. A parsec is the distance at which a star's parallax as viewed from Earth is equal to one second of arc.

See also

References

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  2. ^ Klaus Mainzer and J Eisinger (2002). The Little Book of Time. Springer. ISBN 0387952888. http://books.google.com/books?id=wX111YnexSUC&pg=PA55. . P. 55.
  3. ^ Various (2000). David R. Lide. ed. Handbook of Chemistry and Physics (81st ed.). CRC. ISBN 0849304814. 
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  8. ^ NASA Neptune factsheet and NASA Solar System Exploration Neptune Factsheet NASA Retrieved on 2008-11-17
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  10. ^ NASA/JPL (2009). "Cassini's Big Sky: The View from the Center of Our Solar System". http://www.jpl.nasa.gov/news/features.cfm?feature=2370&msource=F20091119&tr=y&auid=5615216. Retrieved 2009-12-20. 
  11. ^ Fahr, H. J.; Kausch, T.; Scherer, H. (2000). "A 5-fluid hydrodynamic approach to model the Solar System-interstellar medium interaction" (PDF). Astronomy & Astrophysics 357: 268. Bibcode 2000A&A...357..268F. http://aa.springer.de/papers/0357001/2300268.pdf.  See Figures 1 and 2.
  12. ^ "JPL Small-Body Database Browser: 136199 Eris (2003 UB313)". 2008-10-04 last obs. http://ssd.jpl.nasa.gov/sbdb.cgi?sstr=Eris. Retrieved 2009-01-21.  (Aphelion of Eris, the farthest known scattered disk object)
  13. ^ Alessandro Morbidelli. "Origin and dynamical evolution of comets and their reservoirs". arXiv:astro-ph/0512256. 
  14. ^ Littmann, Mark (2004). Planets Beyond: Discovering the Outer Solar System. Courier Dover Publications. pp. 162–163. ISBN 9780486436029. 
  15. ^ Mark Anderson, "Don't stop till you get to the Fluff", New Scientist no. 2585, 6 January 2007, pp. 26-30
  16. ^ DM Seifr et al (1999). "Mapping the Countours of the Local Bubble". Astronomy and Astrophysics 346: 785–797. Bibcode 1999A&A...346..785S. 
  17. ^ Local Chimney and Superbubbles, Solstation.com
  18. ^ S. B. Popov, M. Colpi, M. E. Prokhorov, A. Treves and R. Turolla (2003). "Young isolated neutron stars from the Gould Belt". Astronomy and Astrophysics 406 (1): 111–117. arXiv:astro-ph/0304141. Bibcode 2003A&A...406..111P. doi:10.1051/0004-6361:20030680. http://www.aanda.org/index.php?option=article&access=standard&Itemid=129&url=/articles/aa/abs/2003/28/aah4133/aah4133.html. Retrieved 2009-10-02. 
  19. ^ Harold Spencer Jones, T. H. Huxley, Proceedings of the Royal Institution of Great Britain, Royal Institution of Great Britain, v. 38-39
  20. ^ Eisenhauer, F.; et al. (2003). "A Geometric Determination of the Distance to the Galactic Center". Astrophysical Journal 597 (2): L121–L124. arXiv:astro-ph/0306220. Bibcode 2003ApJ...597L.121E. doi:10.1086/380188. 
  21. ^ Leong, Stacy (2002). "Period of the Sun's Orbit around the Galaxy (Cosmic Year)". The Physics Factbook. http://hypertextbook.com/facts/2002/StacyLeong.shtml. 
  22. ^ Christian, Eric; Samar, Safi-Harb. "How large is the Milky Way?". http://imagine.gsfc.nasa.gov/docs/ask_astro/answers/980317b.html. Retrieved 2007-11-28. 
  23. ^ Frommert, H.; Kronberg, C. (August 25, 2005). "The Milky Way Galaxy". SEDS. http://www.seds.org/messier/more/mw.html. Retrieved 2007-05-09. 
  24. ^ I. D. Karachentsev, V. E. Karachentseva, W. K. Hutchmeier, D. I. Makarov (2004). "A Catalog of Neighboring Galaxies". Astronomical Journal 127 (4): 2031–2068. Bibcode 2004AJ....127.2031K. doi:10.1086/382905. 
  25. ^ Andreas Brunthaler, Mark J. Reid, et. al. (4 March 2005). "The Geometric Distance and Proper Motion of the Triangulum Galaxy (M33)". Science 307 (5714): 1440–1443. arXiv:astro-ph/0503058. Bibcode 2005Sci...307.1440B. doi:10.1126/science.1108342. PMID 15746420. 
  26. ^ "The Local Group of Galaxies". University of Arizona. Students for the Exploration and Development of Space. http://seds.lpl.arizona.edu/messier/More/local.html. Retrieved 2009-10-02. 
  27. ^ cfa.harvard.edu, The Geometry of the Local Supercluster, John P. Huchra, 2007 (accessed 12-12-2008)
  28. ^ "Stars, Galaxies and Cosmology". Department of Mathematics, University of Auckland. http://www.math.auckland.ac.nz/~sharp/cce_astronomy/superclusters-of-galaxies.pdf. Retrieved 2009-10-03. 
  29. ^ John noble Wilford (1987-11-10). "Massive Clusters of Galaxies Defy Concepts of the Universe". New York Times. http://www.nytimes.com/1987/11/10/science/massive-clusters-of-galaxies-defy-concepts-of-the-universe.html?pagewanted=all. Retrieved 2009-11-01. 
  30. ^ Mackie, Glen (2002-02-01). "To see the Universe in a Grain of Taranaki Sand". Swinburne University. http://astronomy.swin.edu.au/~gmackie/billions.html. Retrieved 2006-12-20. 
  31. ^ Lineweaver, Charles; Tamara M. Davis (2005). "Misconceptions about the Big Bang". Scientific American. http://www.sciam.com/article.cfm?id=misconceptions-about-the-2005-03&page=5. Retrieved 2008-11-06. 
  32. ^ "How often does the Sun pass through a spiral arm in the Milky Way?". Cornell University. http://curious.astro.cornell.edu/question.php?number=402. Retrieved 2009-10-03. 
Earth's location in the universe
Each arrow should be read as "within" or "part of".