First Cambridge Catalogue of Radio Sources

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First Cambridge Catalogue of Radio Sources
Alternative names 1C
Survey type Astronomical survey   Blue pencil.svg
Organization Cavendish Astrophysics Group   Blue pencil.svg
Wavelength 3.7 metre  Blue pencil.svg

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".


The 1C catalogue listed about 50 radio sources, detected at 3.7 m with a fixed meridian interferometer. According to researchers at the Special Astrophysical Observatory , most of the sources from 1C were later recognized to be the effect of confusion, i.e. they were not real objects.

The survey was produced using the Long Michelson Interferometer at the Old Rifle Range in Cambridge in 1950. This device operated primarily at a wavelength of 3.7 metres, with an aperture of 110λ, and was operated using Ryle's phase switching technique. Francis Graham-Smith also used the interferometer to measure the electron density in the ionosphere.

The Long Michelson Interferometer was a radio telescope interferometer built by Martin Ryle and co-workers in the late 1940s beside the rifle range to the west of Cambridge, England. The interferometer consisted of 2 fixed elements 440m apart to survey the sky using Earth rotation. It produced the Preliminary survey of the radio stars in the Northern Hemisphere at 45 MHz - 214 MHz. The telescope was operated by the Radio Astronomy Group of Cambridge University.

Cambridge City and non-metropolitan district in England

Cambridge is a university city and the county town of Cambridgeshire, England, on the River Cam approximately 50 miles (80 km) north of London. At the United Kingdom Census 2011, its population was 123,867 including 24,506 students. Cambridge became an important trading centre during the Roman and Viking ages, and there is archaeological evidence of settlement in the area as early as the Bronze Age. The first town charters were granted in the 12th century, although modern city status was not officially conferred until 1951.

Martin Ryle English radio astronomer

Sir Martin Ryle was an English radio astronomer who developed revolutionary radio telescope systems and used them for accurate location and imaging of weak radio sources. In 1946 Ryle and Derek Vonberg were the first people to publish interferometric astronomical measurements at radio wavelengths. With improved equipment, Ryle observed the most distant known galaxies in the universe at that time. He was the first Professor of Radio Astronomy at the University of Cambridge, and founding director of the Mullard Radio Astronomy Observatory. He was Astronomer Royal from 1972 to 1982. Ryle and Antony Hewish shared the Nobel Prize for Physics in 1974, the first Nobel prize awarded in recognition of astronomical research. In the 1970s, Ryle turned the greater part of his attention from astronomy to social and political issues which he considered to be more urgent.

The catalogue from this survey is only informally known as the 1C catalogue.

List of sources

NumberRAErrorDecErrorIntensity§MagnitudeCurrent designation
After Ryle, et al. [1]

§ Intensity is in Watts metres−2 (c./s.)−1 x 1025

Note that the position can be specified more accurately for sources of small declination, since the nature of the instrument is such as to make the table errors overstated if the axis is not exactly East-West.


The survey found radio sources in close proximity to four of the five major extragalactic nebulae, namely M31, M33, M101 and M51, corresponding to sources 00.01, 01.01, 14.01 and 13.01 respectively. Only M81 had no observed radio source.

Messier 81 spiral galaxy in the constellation Ursa Major

Messier 81 is a spiral galaxy about 12 million light-years away, with a diameter of 90,000 light years, about half the size of the Milky Way, in the constellation Ursa Major. Due to its proximity to Earth, large size, and active galactic nucleus, Messier 81 has been studied extensively by professional astronomers. The galaxy's large size and relatively high brightness also makes it a popular target for amateur astronomers.

The isotropy of the sources lead the team to conclude that radio stars were either local phenomena, or extragalactic.

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  1. Ryle M; Smith F G & Elsmore B (August 1950). "A Preliminary Survey of Radio Stars in the Northern Hemisphere". Monthly Notices of the Royal Astronomical Society. 110: 514. Bibcode:1950MNRAS.110..508R. doi:10.1093/mnras/110.6.508.