Second Cambridge Catalogue of Radio Sources

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Second Cambridge Catalogue of Radio Sources
Alternative names 2C
Survey type astronomical survey Blue pencil.svg
Organization Cavendish Astrophysics Group Blue pencil.svg
Observations Cambridge Interferometer Blue pencil.svg
Wavelength 81.5 megahertz Blue pencil.svg

The Second Cambridge Catalogue of Radio Sources (2C) was published in 1955 by John R Shakeshaft and colleagues. It comprised a list of 1936 sources between declinations -38 and +83, giving their right ascension, declination, both in 1950.0 coordinates, and flux density. The observations were made with the Cambridge Interferometer, at 81.5 MHz.

Declination Astronomical coordinate analogous to latitude

In astronomy, declination is one of the two angles that locate a point on the celestial sphere in the equatorial coordinate system, the other being hour angle. Declination's angle is measured north or south of the celestial equator, along the hour circle passing through the point in question.

Right ascension Astronomical equivalent of longitude

Right ascension is the angular distance of a particular point measured eastward along the celestial equator from the Sun at the March equinox to the point above the earth in question. When paired with declination, these astronomical coordinates specify the direction of a point on the celestial sphere in the equatorial coordinate system.

The jansky is a non-SI unit of spectral flux density, or spectral irradiance, used especially in radio astronomy. It is equivalent to 10−26 watts per square metre per hertz.

The data appeared to show a flux/number ('source counts') trend which precluded some cosmological models (such as the Steady-State):-

The source counts distribution of radio-sources from a radio-astronomical survey is the cumulative distribution of the number of sources (N) brighter than a given flux density (S). Because it is usually plotted with the log-log scale, so its distribution is also called as the log N – log S plot. It is one out of a half-dozen cosmological tests that was conceived in the 1930s to check the viability of and compare new cosmological models.

For a uniform distribution of radio sources the slope of the cumulative distribution of log(number, N) versus log (power, S) would have been -1.5, but the Cambridge data apparently implied a (log(N),log(S)) slope of nearly -3.0.

Unfortunately, this interpretation was premature as a significant number of the sources listed were later found to be the product of 'confusion', the blending of several weaker sources in the lobes of the interferometer to produce the apparent effect of a single stronger source. Key data demonstrating this came from the then-recently commissioned Mills Cross Telescope in Australia. However, subsequent statistical analysis by Hewish of the interferometer records later showed some aspects of the initial interpretation to have been broadly correct, with the correct measure of the (log(N),log(S)) slope of nearly -1.8 derived once confusion was taken into account.

The Mills Cross Telescope was a two-dimensional radio telescope built by Bernard Mills in 1954 at the Fleurs field station of the Australian Commonwealth Scientific and Industrial Research Organisation in the area known now as Badgerys Creek, about 40 km west of Sydney, New South Wales, Australia.

Antony Hewish is a British radio astronomer who won the Nobel Prize for Physics in 1974 for his role in the discovery of pulsars. He was also awarded the Eddington Medal of the Royal Astronomical Society in 1969.

The survey was superseded by the much more reliable 3C and 3CR surveys. The 3C survey also used the Cambridge Interferometer, but at 159 MHz, which helped significantly reduce the 'confusion' (see above) in the later survey.

The Third Cambridge Catalogue of Radio Sources (3C) is an astronomical catalogue of celestial radio sources detected originally at 159 MHz, and subsequently at 178 MHz.

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The First Cambridge Catalogue of Radio Sources (1C) refers to the catalogue listed in the article Ryle M, Smith F G & Elsmore B (1950) MNRAS vol 110 pp508-523 "A Preliminary Survey of Radio Stars in the Northern Hemisphere".

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