question: How do we know the what the large scale structures of the universe look like?
comment: I once read this article about [galactic supercluster Laniakea]( URL_0 ) in Scientific American, and it made me feel so small I had to stop and hang on to the table. The sheer scale of these observations is mind blowing, but they cover some of the methodology in that article. Large scale observations and massive computational modeling are a big part of it.
passages: Understanding the formation and evolution of the largest and earliest structures (i.e., quasars, galaxies, clusters and superclusters) is one of the largest efforts in cosmology. Cosmologists study a model of hierarchical structure formation in which structures form from the bottom up, with smaller objects forming first, while the largest objects, such as superclusters, are still assembling. One way to study structure in the universe is to survey the visible galaxies, in order to construct a three-dimensional picture of the galaxies in the universe and measure the matter power spectrum. This is the approach of the "Sloan Digital Sky Survey" and the 2dF Galaxy Redshift Survey.
   These and other tools are used by different scientists at the IATE to perform original and reliable astronomical research.
  
  Section::::Scientific Areas.:Large Scale Structure of the Universe.
  
  The large-scale structure of the Universe is the field of cosmology that studies the distribution of the matter in the Universe on the largest scales. This field has grown remarkably since the '80s, with the development of three-dimensional maps of galaxies in several bands of the electromagnetic spectrum, and with the observation of the Cosmic Microwave Background (CMB).
   BULLET::::- Some structures are far too distant to be seen even with the most powerful telescopes. Some factors are included to explain the structure (like gravitational lensing and redshift data).
  
  BULLET::::- Some structures have no defined limits, or endpoints. All structures are believed to be part of the cosmic web, which is a conclusive idea. Most structures are overlapped by nearby galaxies, creating a problem of how to carefully define the structure's limit.
  
  Section::::List of largest voids.
   Additional science goals for CLASS are to better understand our own Milky Way Galaxy and to search for evidence of exotic new physics through circular polarization in the CMB and large-scale anomalies. (See the Low multipoles and other anomalies section of the cosmic microwave background article for more information on the latter.)
  
  Section::::Instrument.
   The organization of structure arguably begins at the stellar level, though most cosmologists rarely address astrophysics on that scale. Stars are organized into galaxies, which in turn form galaxy groups, galaxy clusters, superclusters, sheets, walls and filaments, which are separated by immense voids, creating a vast foam-like structure sometimes called the "cosmic web". Prior to 1989, it was commonly assumed that virialized galaxy clusters were the largest structures in existence, and that they were distributed more or less uniformly throughout the universe in every direction. However, since the early 1980s, more and more structures have been discovered. In 1983, Adrian Webster identified the Webster LQG, a large quasar group consisting of 5 quasars. The discovery was the first identification of a large-scale structure, and has expanded the information about the known grouping of matter in the universe. In 1987, Robert Brent Tully identified the Pisces–Cetus Supercluster Complex, the galaxy filament in which the Milky Way resides. It is about 1 billion light-years across. That same year, an unusually large region with a much lower than average distribution of galaxies was discovered, the Giant Void, which measures 1.3 billion light-years across. Based on redshift survey data, in 1989 Margaret Geller and John Huchra discovered the "Great Wall", a sheet of galaxies more than 500 million light-years long and 200 million light-years wide, but only 15 million light-years thick. The existence of this structure escaped notice for so long because it requires locating the position of galaxies in three dimensions, which involves combining location information about the galaxies with distance information from redshifts.
   Section::::Key projects.:Galaxies, cosmology, dark matter and dark energy.
  
  The sensitivity of the SKA in the 21 cm hydrogen line will map a billion galaxies out to the edge of the observable Universe. The large-scale structure of the cosmos revealed will give constraints to determine the processes resulting in galaxy formation and evolution. Imaging hydrogen through the Universe will provide a three-dimensional picture of the first ripples of structure that formed individual galaxies and clusters. This may also allow the measurement of effects hypothetically caused by dark energy and causing the increasing rate of expansion of the universe.
   BULLET::::- 1998 — The 2dF Galaxy Redshift Survey maps the large-scale structure in a section of the Universe close to the Milky Way
  
  BULLET::::- 1998 — Hubble Deep Field South
  
  BULLET::::- 1998 — Discovery of accelerating universe
  
  BULLET::::- 2000 — Data from several cosmic microwave background experiments give strong evidence that the Universe is "flat" (space is not curved, although space-time is), with important implications for the formation of large-scale structure
  
  Section::::Early 21st century.
  
  BULLET::::- 2001 — First data release from the ongoing Sloan Digital Sky Survey
  
  BULLET::::- 2004 — The European Southern Observatory discovers Abell 1835 IR1916, the most distant galaxy yet seen from Earth.
   If the observable universe encompasses the entire universe, we may be able to determine the structure of the entire universe by observation. However, if the observable universe is smaller than the entire universe, our observations will be limited to only a part of the whole, and we may not be able to determine its global geometry through measurement. From experiments, it is possible to construct different mathematical models of the global geometry of the entire universe all of which are consistent with current observational data and so it is currently unknown whether the observable universe is identical to the global universe or it is instead many orders of magnitude smaller than it. The universe may be small in some dimensions and not in others (analogous to the way a cuboid is longer in the dimension of length than it is in the dimensions of width and depth). To test whether a given mathematical model describes the universe accurately, scientists look for the model's novel implications—what are some phenomena in the universe that we have not yet observed, but that must exist if the model is correct—and they devise experiments to test whether those phenomena occur or not. For example, if the universe is a small closed loop, one would expect to see multiple images of an object in the sky, although not necessarily images of the same age.
   List of largest cosmic structures
  
  This is a list of the largest cosmic structures so far discovered. The unit of measurement used is the light-year (distance traveled by light in one Julian year; approximately 9.46 trillion kilometres).
  
  This list includes superclusters, galaxy filaments and large quasar groups (LQGs). The list characterizes each structure based on its longest dimension.
   In America, the US HOU project is led by the United States with support from the National Science Foundation, the Department of Defense, and the Department of Energy. In the USA, HOU has developed and pilot tested an educational program that enables high school students to request their own observations from professional observatories. Students download telescope images to their classroom computers and use the powerful HOU image processing software to visualize and analyze their data. High school curriculum developed by HOU integrates many of the science and math topics and skills outlined in national standards into open-ended astronomical investigations. HOU has also developed activities and tools for middle school students and products for informal science education centers. The Lawrence Hall of Science at University of California, Berkeley, is the educational center for the HOU project.
   Another tool for understanding structure formation is simulations, which cosmologists use to study the gravitational aggregation of matter in the universe, as it clusters into filaments, superclusters and voids. Most simulations contain only non-baryonic cold dark matter, which should suffice to understand the universe on the largest scales, as there is much more dark matter in the universe than visible, baryonic matter. More advanced simulations are starting to include baryons and study the formation of individual galaxies. Cosmologists study these simulations to see if they agree with the galaxy surveys, and to understand any discrepancy.
   BULLET::::- 1991 — Donald Gudehus discovers a serious systematic bias in certain cluster galaxy data (surface brightness vs. radius parameter, and the formula_1 method) which affect galaxy distances and evolutionary history; he devises a new distance indicator, the reduced galaxian radius parameter, formula_2, which is free of biases,
  
  BULLET::::- 1992 — First detection of large-scale structure in the Cosmic microwave background indicating the seeds of the first clusters of galaxies in the early Universe
  
  BULLET::::- 1995 — First detection of small-scale structure in the cosmic microwave background
  
  BULLET::::- 1995 — Hubble Deep Field survey of galaxies in field 144 arc seconds across.
   Superclusters form massive structures of galaxies, called "filaments", "supercluster complexes", "walls" or "sheets", that may span between several hundred million light-years to 10 billion light-years, covering more than 5% of the observable universe. These are the largest known structures to date. Observations of superclusters can give information about the initial condition of the universe, when these superclusters were created. The directions of the rotational axes of galaxies within superclusters may also give insight and information into the early formation process of galaxies in the history of the Universe.
   BULLET::::- (The latter two surveys are joining together observations obtained from space with the Hubble Space Telescope, the Spitzer Space Telescope, the Chandra X-ray Observatory and the XMM-Newton satellite, with a large set of observations obtained with ground-based telescopes).
  
  BULLET::::- Atlas 3d Survey – sample of 260 galaxies for the Astrophysics project.
  
  BULLET::::- Planned
  
  BULLET::::- Large Synoptic Survey Telescope – a proposed very large telescope designed to repeatedly survey the whole sky that is visible from its location
  
  BULLET::::- ASKAP HI All Sky Survey (WALLABY) – PI Bärbel Koribalski
  
  Section::::List of sky surveys.:Surveys of the Magellanic Clouds.
   BULLET::::- 1989 — Margaret Geller and John Huchra discover the "Great Wall", a sheet of galaxies more than 500 million light years long and 200 million wide, but only 15 million light years thick,
  
  BULLET::::- 1990 — Michael Rowan-Robinson and Tom Broadhurst discover that the IRAS galaxy IRAS F10214+4724 is the brightest known object in the Universe,
   BULLET::::- 12th century — Avempace (Ibn Bajjah) of Islamic Spain proposes the Milky Way to be made up of many stars but that it appears to be a continuous image due to the effect of refraction in the Earth's atmosphere,
  
  BULLET::::- 14th century — Ibn Qayyim Al-Jawziyya of Syria proposes the Milky Way galaxy to be "a myriad of tiny stars packed together in the sphere of the fixed stars" and that these stars are larger than planets,
  
  BULLET::::- 1521 — Ferdinand Magellan observes the Magellanic Clouds during his circumnavigating expedition,
   In 2005 Masters moved to Harvard University to work as a postdoctoral researcher with John Huchra on a project to make the most complete map of the local Universe. Masters "unveiled the most complete 3-D map of the local universe (out to a distance of 380 million light-years) ever created" in 2011 at the 218th meeting of the American Astronomical Society. The map was created using data from the Two-Micron All-Sky Survey.
   The universe can be viewed as having a hierarchical structure. At the largest scales, the fundamental component of assembly is the galaxy. Galaxies are organized into groups and clusters, often within larger superclusters, that are strung along great filaments between nearly empty voids, forming a web that spans the observable universe.
   Section::::Areas of study.:Formation and evolution of large-scale structure.
   Before a reconstruction can be made, the orientation of the object in each image needs to be estimated. Several methods have been developed to work out the relative Euler angles of each image. Some are based on common lines (common 1D projections and sinograms), others use iterative projection matching algorithms. The latter works by beginning with a simple, low resolution 3D starting model and compares the experimental images to projections of the model and creates a new 3D to bootstrap towards a solution.
   Timeline of knowledge about galaxies, clusters of galaxies, and large-scale structure
  
  Timeline of galaxies, clusters of galaxies, and large-scale structure of the universe
  
  Section::::Pre-20th century.
  
  BULLET::::- 5th century BC — Democritus proposes that the bright band in the night sky known as the Milky Way might consist of stars,
   BULLET::::- 1977 — R. Brent Tully and Richard Fisher publish the Tully–Fisher relation between the luminosity of an isolated spiral galaxy and the velocity of the flat part of its rotation curve,
  
  BULLET::::- 1978 — Steve Gregory and Laird Thompson describe the Coma supercluster,
  
  BULLET::::- 1978 — Donald Gudehus finds evidence that clusters of galaxies are moving at several hundred kilometers per second relative to the cosmic microwave background radiation,
   Other, complementary observations to measure the distribution of matter in the distant universe and to probe reionization include:
  
  BULLET::::- The Lyman-alpha forest, which allows cosmologists to measure the distribution of neutral atomic hydrogen gas in the early universe, by measuring the absorption of light from distant quasars by the gas.
  
  BULLET::::- The 21 centimeter absorption line of neutral atomic hydrogen also provides a sensitive test of cosmology.
  
  BULLET::::- Weak lensing, the distortion of a distant image by gravitational lensing due to dark matter.
  
  These will help cosmologists settle the question of when and how structure formed in the universe.
   The 2dF survey also yields a unique view on our local cosmic environment. In the figure a 3-D reconstruction of the inner parts of the survey is shown, revealing an impressive view on the cosmic structures in the nearby universe. Several superclusters stand out, such as the Sloan Great Wall, one of the largest structures in the universe known to date (see also Huge-LQG).
  
  Section::::See also.
  
  BULLET::::- Lambda-CDM model
  
  BULLET::::- Dark matter
  
  Section::::External links.
  
  BULLET::::- Official site of the 2dF Galaxy Redshift Survey
   Cosmology Large Angular Scale Surveyor
  
  The Cosmology Large Angular Scale Surveyor (CLASS) is an array of microwave telescopes at a high-altitude site in the Atacama Desert of Chile as part of the Parque Astronómico de Atacama. The CLASS experiment aims to test the theory of cosmic inflation and distinguish between inflationary models of the very early universe by making precise measurements of the polarization of the Cosmic Microwave Background (CMB) over 65% of the sky at multiple frequencies in the microwave region of the electromagnetic spectrum.
  
  Section::::Science goals.
  
raw_presuppositions: We need pictures to know what large scale structures of the universe look like.
raw_corrections: We can use computational modeling to guess what large scale structures in the universe look like.