Second Cambridge Catalogue of Radio Sources
Encyclopedia
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 declination
s -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.
The data appeared to show a flux/number ('source counts
') trend which precluded some cosmological models (such as the Steady-State
):-
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 appears to have been premature - 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.
The survey was superseded by the much more reliable 3C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.
Declination
In astronomy, declination is one of the two coordinates of the equatorial coordinate system, the other being either right ascension or hour angle. Declination in astronomy is comparable to geographic latitude, but projected onto the celestial sphere. Declination is measured in degrees north and...
s -38 and +83, giving their right ascension
Right ascension
Right ascension is the astronomical term for one of the two coordinates of a point on the celestial sphere when using the equatorial coordinate system. The other coordinate is the declination.-Explanation:...
, declination
Declination
In astronomy, declination is one of the two coordinates of the equatorial coordinate system, the other being either right ascension or hour angle. Declination in astronomy is comparable to geographic latitude, but projected onto the celestial sphere. Declination is measured in degrees north and...
, both in 1950.0 coordinates, and flux density
Jansky
The flux unit or jansky is a non-SI unit of spectral flux density equivalent to 10−26 watts per square metre per hertz...
. The observations were made with the Cambridge Interferometer
Cambridge Interferometer
The Cambridge Interferometer was a radio telescope interferometer built by Martin Ryle and Antony Hewish in the early 1950s to the west of Cambridge . The interferometer consisted of an array of 4 fixed elements to survey the sky...
, at 81.5 MHz.
The data appeared to show a flux/number ('source counts
Source counts
The source counts distribution of radio-sources from a radio-astronomical survey is the cumulative distribution of the number of sources brighter than a given flux density...
') trend which precluded some cosmological models (such as the Steady-State
Steady State theory
In cosmology, the Steady State theory is a model developed in 1948 by Fred Hoyle, Thomas Gold, Hermann Bondi and others as an alternative to the Big Bang theory...
):-
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 appears to have been premature - 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
Mills Cross Telescope
Bernard Mills built the two-dimensional Mills Cross Telescope 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 40km west of Sydney, New South Wales, Australia.Each arm of the cross was...
in Australia).
However, subsequent statistical analysis by Hewish
Antony Hewish
Antony Hewish FRS is a British radio astronomer who won the Nobel Prize for Physics in 1974 for his work on the development of radio aperture synthesis and its role in the discovery of pulsars...
of the interferometer records later showed some aspects of the initial interpretation to have been broadly correct.
The survey was superseded by the much more reliable 3C
Third Cambridge Catalogue of Radio Sources
The Third Cambridge Catalogue of Radio Sources is an astronomical catalogue of celestial radio sources detected originally at 159 MHz, and subsequently at 178 MHz. It was published in 1959 by members of the Radio Astronomy Group of the University of Cambridge...
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.