An alternative term for the carbon cycle, named after the physicists who, in the early 1930s, first proposed this sequence of nuclear processes as a source of stellar energy.

Asteroid 250, diameter 128 km, discovered in 1885 by J. Palisa.

Asteroid 1580, diameter 60 km, discovered in 1950 when it made a close approach to the Earth.

One of the small satellites of Uranus discovered during the Voyager 2 encounter with the planet in 1986.

Comet Biela.

Andromedids.

A model for the history of the universe, according to which it began in an infinitely compact state and has been expanding ever since. This apparent beginning occurred between 13 and 20 billion years ago and has come to be known as the Big Bang. The theory is now widely accepted since it explains the two most significant observations in cosmology: the expanding universe and the existence of the cosmic background radiation. The known laws of physics can be used to project backwards and calculate what the universe was like at various stages of its development since 10-43 seconds after the Big Bang. For the first million years, the matter and energy in the universe formed an opaque plasma, sometimes called the primeval fireball. By the end of this period, the expansion of the universe caused the temperature to fall below 3,000 K so that protons and electrons could combine to form hydrogen atoms. At this stage, the universe became transparent to radiation. The density of matter then exceeded that of radiation, where previously the situation was the reverse, and so dictated the rate of expansion of the universe. The microwave background is all that remains of the greatly cooled radiation from the early universe. The first galaxies did not begin to form from the primordial clouds of hydrogen and helium until one or two billion years later. The term big bang may be applied to any model of an expanding universe that had a hot, dense past. See also: steady-state theory.

English name for the constellation Ursa Major.

A observatory located at an altitude of 2,000 metres 6,600 feet on an island in Big Bear Lake in California. The site was chosen to eliminate the distortion caused by turbulence over land heated by the Sun. Formerly owned and operated by the California Institute of Technology, it was transferred in 1997 to the New Jersey Institute of Technology. There are three main telescopes on the same mount: a 65-centimetre 26-inch reflector, a 25-cm 10-inch refractor and a 15-cm 6-inch refractor. The smallest telescope is used to monitor the whole Sun. The 25-cm is equipped with a magnetograph, and there is a spectrograph fed by light from the 65-cm. An additional instrument is dedicated to the study of helioseismology.

The hypothetical total inward collapse of the universe. If its present expansion were to slow down sufficiently, the universe could enter a phase of contraction that would end with the so-called Big Crunch. See also: Big Bang, oscillating universe.

North American name for the asterism in the constellation Ursa Major, also called the Plough.

English name for the constellation Canis Major.

In scientific usage, a thousand million 10 to the power of 9. Formerly, billion was used in the UK to mean a million million, so care with interpretation is needed if there is any possibility of confusion.

A millimetre-wave telescope at Hat Creek Observatory in California, operated by the Berkeley-Illinois-Maryland Association. It consists of ten 6-metre 20-foot dishes operating in the 1-3 mm wavelength region of the spectrum.

A pair of stars in orbit around each other, held together by their mutual gravitational attraction. About half of all stars are in fact binary or multiple, though many are so close that the components cannot be seen individually. The presence of more than one star is inferred from the appearance of the combined spectrum. The two components in a binary system each move in an elliptical orbit around the common centre of mass. The further apart they are, the slower they move. Pairs in which the separation is great enough for the two stars to be distinguished, or split, in a telescope often have orbital periods as long as 50 or 100 years. Such pairs are called visual binaries. If one star is much fainter than the other, its presence may be revealed only by the obvious orbital motion of its brighter companion. Pairs of this type are called astrometric binaries. As the members of a binary system move in orbit, their velocities towards or away from the Earth change in a regular repeating pattern. Through the Doppler effect, these velocity variations are reflected as wavelength changes in the features of the combined spectrum. Study of such a spectrum can reveal details about the nature of the stars and their orbits. Binary stars recognized as such only by means of spectroscopy are called spectroscopic binaries. Their periods usually lie in the range from a day to a few weeks. Some binary components are so close that the pull of gravity distorts the individual stars from their normal spherical shape. They may exchange material and be surrounded by a common envelope of gas. An accretion disc may develop as material streams towards a compact, spinning star in a binary system. The energy released results in the emission of X-rays. Novae are another consequence of mass transfer in binary stars. If the orbits of a binary pair are oriented in space so that one star has to pass in front of the other as seen from the Earth, the system is described as eclipsing. Such a system is observed to be variable since one star periodically blots out light from the other. The best-known eclipsing binary is Algol.