carbon star.

A 1.0-metre 40-inch reflecting telescope in the Isaac Newton Group at the Observatorio del Roque de los Muchachos, La Palma, Canary Islands. It is operated by the Royal Greenwich Observatory. Observing time is shared by the collaborating countries, which are the UK, Eire, Spain and the Netherlands. It is a specialist telescope for photometry and wide-field photography, and came into operation in 1984.

A submillimetre-wave telescope located at the Mauna Kea Observatories on the island of Hawaii. It is managed by the Joint Astronomy Center, Hilo, Hawaii, on behalf of the UK, the Netherlands and Canada, which are the sponsoring countries. It is a Cassegrain design, with a paraboloidal reflector 15 metres 49 feet in diameter. The dish is constructed from 276 lightweight panels supported on a mild steel frame, designed to deform uniformly and so maintain the paraboloid shape when the orientation is changed. The mount is altazimuth. The telescope is inside a rotating protective enclosure; during observations, the viewing aperture is covered with a membrane of woven teflon to protect the surface from wind and heating by the Sun. Only 10 per cent of the submillimetre radiation is absorbed by the membrane. The telescope’s capabilities were extended in 1996 by the provision of a newly developed instrument, which is a combined imaging camera and photometer. Known as SCUBA Submillimetre Common-User Bolometer Array, it consists of two arrays of detectors cooled to below 0.1 K. One array is optimized for use at 850 microns and the other at 450 microns.

The unit of flux density used in radio astronomy. One jansky is 10 to the power of -26 watts per square metre per hertz. The unit is named after Karl Jansky, who discovered radio emission from the Milky Way in 1932.

A small satellite of Saturn, discovered by Audouin Dollfus in 1966 when the ring system was edge-on as seen from Earth. Janus orbits just beyond the outer edge of the ring system and is co-orbital with Epimetheus. The two may be fragments of a larger object that was shattered by an impact. Janus is irregular in shape, measuring 220 × 160 kilometres. See also: co-orbital satellite

Abbreviation for Julian date.

An idealized set of initial conditions for the steady contraction under gravity of a density perturbation in an interstellar cloud.

The minimum wavelength that a density perturbation in a gas cloud must have if it is to grow in response to gravitational forces. The concept is central to theories of star formation in interstellar clouds.

The minimum mass for a density perturbation in an interstellar cloud that can contract under its own gravity.

A narrow beam of matter or radiation emerging, for example, from an active galactic nucleus or from an accretion disc.

An institution in Pasadena, California, operated by the California Institute of Technology Caltech in support of programmes of the US National Aeronautics and Space Administration NASA and of other agencies. It is distinguished as the primary facility in the USA for the development and operation of interplanetary space probes. Activities managed by JPL have included the Viking, Voyager, Galileo and Magellan projects. Although often referred to as a NASA centre, JPL employees are not US government civil servants, unlike, for example, those who work at the Goddard Space Flight Center and similar establishments that are formally part of NASA.

An open star cluster in the constellation Crux. Its brightest member is the sixth magnitude blue supergiant star Kappa Crucis. There are a number of blue and red supergiants, resulting in an impressive appearance in a small telescope; this contrast is said to be why John Herschel gave the cluster the name Jewel Box. The cluster’s distance is 7,800 light years.

Abbreviation for Joint Institute for Laboratory Astrophysics.

Abbreviation for Jacobus Kapteyn Telescope.

The location in Cheshire of the Nuffield Radio Astronomy Laboratories of the University of Manchester.