Abbreviation for California Association for Research in Astronomy.

A peculiar, ringed Seyfert galaxy near NGC 1595 and NGC 1598.

A group of three galaxies, NGC 1595, NGC 1598 and the Carafe Galaxy, which share a common motion in space. NGC 1598 has two luminous jets projecting from it, and there is evidence that interaction has occurred between the Carafe Galaxy and NGC 1595.

A series of nuclear reactions, believed to take place in stars and to be one of the main sources of stellar energy, in which hydrogen is converted to helium. The six stages in the process are: 12C + 1H -> 13N + gamma-ray photon 13N -> 13C + positron + neutrino 1H + 13C -> 14N + gamma-ray photon 1H + 14N -> 15O + gamma-ray photon 15O -> 15N + positron + neutrino 1H + 15N -> 12C + 4He Thus, the 12C nucleus reappears at the end. The process cannot take place unless carbon is present, but relatively few 12C nuclei are required. The rate at which the carbon cycle occurs depends very sharply on temperature. A minimum temperature of 14 million K is needed for it to take place at all. Above 16 million K it dominates over the other main hydrogen-burning process, the proton-proton chain, and is believed to be the primary source of energy in relatively hot stars with masses greater than two or three times that of the Sun. Two longer variations on the sequence are also thought to occur, the CNO bi-cycle and the CNO tri-cycle, which result in the creation of 14N and 15N, respectively, rather than the reappearance of carbon. In the shorthand used to represent nuclear reactions, the CNO bi-cycle proceeds as: 15Np,γ 16Op,γ 17F,β+ +ν 17Op,α 14N. The CNO tri-cycle includes the additional stages: 17Op,γ 18F,&bata;++ν 18Op, α 15N

A general name for a group of peculiar, red giant stars whose spectra show strong bands of molecular carbon, CN, CH or other carbon compounds, and not the more typical TiO. In the original Harvard classification system of 1918, the carbon stars were allocated to spectral types R and N. It was found that they have temperatures similar to those of the more common K stars and M stars and that the differences in the spectra arise from differences in the abundance of carbon and oxygen. The term carbon star was introduced in the 1940s by Morgan and Keenan, who proposed a new sequence of classes from C0 to C7, paralleling the decreasing temperature sequence in normal stars from G4 to M4. Though known carbon stars are rare in our own Galaxy, many thousands have been discovered in the Large and Small Magellanic Clouds. Some carbon stars contain the unstable element technetium, the longest-lived isotope of which has a half-life of only 210,000 years, a short period on astronomical timescales. A few less than twenty of the coolest carbon stars show an extremely strong line of lithium in their spectra. It is also possible to measure the proportions present of two isotopes of carbon, 12C and 13C. In the carbon stars, particularly the hotter ones, these proportions differ significantly from those encountered in the solar system. A group in which the ratio 12C /13C is unusually low are known as J stars.

A rare type of stony meteorite. Because their average chemical composition is very similar to that of the Sun apart from the hydrogen and helium and there is a relatively high abundance of volatile material, carbonaceous chondrites are thought to represent some of the primitive, unprocessed material from which the solar system formed. They are made up of a matrix of carbon-rich minerals in which the chondrules are embedded. The water content can be as high as 20 per cent. The largest known example is the Allende meteorite.

The four directions north, south, east and west.

A large constellation in the southern Milky Way, formerly part of Argo Navis. It contains the second-brightest star in the sky, Canopus.

Eta Carinae Nebula.

A small satellite of Jupiter number XI, discovered in 1938 by S. B. Nicholson.

A range of mountains on the Moon forming part of the border of the Mare Imbrium.

A number that identifies each rotation of the Sun. The sequence began with rotation number one on 9 November 1853. The system was started by R. C. Carrington, who employed the average synodic rotation rate for sunspots, which he had determined as 27.2753 days. Since the Sun does not rotate as a solid body, the rate actually varies with latitude.

An ambitious project, started in 1887, intended to produce photographic charts of the entire sky, together with an associated star catalogue. The charts were never completed, the standard methods ultimately being overtaken by technical advances in astrophotography. During the 1880s, the growing importance of photography in astronomy became apparent. In 1885, a 34-cm 13.5-inch photographic refractor was constructed at the Paris Observatory by Paul and Prosper Henry. Impressed by their achievements, the Director, E. B. Mouchez, with encouragement from Sir David Gill and Otto Struve, organized the Astrographic Congress of April 1887. The permanent committee met five times before it was transferred to the auspices of the International Astronomical Union in 1919. The work was initially divided among eighteen observatories, though notably none in the USA. The Paris instrument was adopted as the standard prototype. Each plate was to be two degrees square with a superimposed grid of fine lines at 5-mm 0.2-inch intervals. A total of about 22,000 plates was taken, only a quarter of the number originally projected. However, the publication of the associated Astrographic Catalogue was finally completed in 1964.

A popular name for a peculiar galaxy, 500 million light years away, otherwise known as A0035. It consists of a circular rim, 170,000 light years in diameter, inside which are a hub and spokes made up of old red stars. It is believed that the galaxy was once a normal large spiral galaxy through which a smaller galaxy passed a few hundred million years ago. The intruder can still be seen near by. The shock of the collision caused the formation of large numbers of massive stars in the rim. As a result, the rate at which supernovae occur now is about a hundred times greater than in a normal galaxy.

An adjective used to describe any type of optical, radio or other telescope design which incorporates the use of a central hole in the primary reflecting element. See also: Cassegrain telescope.