The Center for Astrophysics (CfA)

Redshift Survey In astronomy, a redshift survey is a astronomical surveys, survey of a section of the sky to measure the redshift of astronomical objects: usually galaxies, but sometimes other objects such as galaxy clusters or quasars. Using Hubble's law, the ...

was the first attempt to map the

large-scale structure of the universe The observable universe is a spherical region of the universe consisting of all matter that can be observed from Earth; the electromagnetic radiation from these objects has had time to reach the Solar System and Earth since the beginning of th ...

. The first survey began in 1977 with the objective of calculating the velocities of the brighter galaxies in the nearby universe by measuring their

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 increase in frequency and e ...

s at the

Smithsonian Astrophysical Observatory The Smithsonian Astrophysical Observatory (SAO) is a research institute of the Smithsonian Institution, concentrating on Astrophysics, astrophysical studies including Galactic astronomy, galactic and extragalactic astronomy, cosmology, Sun, solar ...

in Cambridge, Massachusetts. The redshift is the relative increase in the wavelength emitted by a light source, in this case a galaxy, moving away from an observer from which its speed and then, using

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 a galaxy is from the Earth, the faste ...

, its distance can be calculated. A 3-dimensional map of that part of the Universe could thus be produced. This initial data collection was completed by 1982. The second survey (CfA2) was started in 1985 by John Huchra and Margaret Geller and measured the redshifts of 18,000 bright galaxies in the Northern sky by 1995. Data from the second CfA survey showed that galaxies were not evenly distributed but clustered on the spherical surfaces of empty "voids". The project also made the 1989 discovery of the ''

Great Wall The Great Wall of China (, literally "ten thousand Li (unit), ''li'' long wall") is a series of fortifications in China. They were built across the historical northern borders of ancient Chinese states and Imperial China as protection agains ...

'', a

supercluster A supercluster is a large group of smaller galaxy clusters or galaxy groups; they are among the largest known structures in the universe. The Milky Way is part of the Local Group galaxy group (which contains more than 54 galaxies), which in tu ...

galaxies A galaxy is a system of stars, stellar remnants, interstellar gas, dust, and 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 Sys ...

M. J. Geller & J. P. Huchra, Science 246, 897 (1989)
Retrieved April 7, 2007 surrounded by voids that surprised astronomers because its size was larger than could be produced by

gravitational collapse Gravitational collapse is the contraction of an astronomical object due to the influence of its own gravity, which tends to draw matter inward toward the center of gravity. Gravitational collapse is a fundamental mechanism for structure formati ...

since the beginning of the universe. Since then, superclusters have been described as artifacts of

quantum fluctuation In quantum physics, a quantum fluctuation (also known as a vacuum state fluctuation or vacuum fluctuation) is the temporary random change in the amount of energy in a point in space, as prescribed by Werner Heisenberg's uncertainty principle. ...

s in the

inflationary epoch __NOTOC__ In physical cosmology, the inflationary epoch was the period in the evolution of the early universe when, according to inflation theory, the universe underwent an extremely rapid exponential expansion. This rapid expansion increased th ...

of the universe.

References

{{Portal bar, Astronomy, Stars, Outer space Observational astronomy Large-scale structure of the cosmos Astronomical surveys 1977 in science