An adjective used to describe the phase of illumination of a body shining by reflected sunlight, such as the Moon, when it is between half and full.

A Japanese X-ray astronomy satellite launched on 5 February 1987, originally called Astro-C.

A European Space Agency probe, which encountered Halley’s Comet in March 1986. Up to two seconds before closest approach, a distance of 605 kilometres from the nucleus, all experiments worked perfectly. At that moment, a collision with a small particle caused the craft to wobble so that the communications antenna was not directed towards Earth. Communications were re-established after the encounter. The multicolour camera returned images, including close-ups of the nucleus, until the moment when contact was lost; it was subsequently destroyed by impacts. The other instruments on board included a dust impact detector and an ion mass spectrometer, which observed that the gas in the coma is 80 per cent water by mass. When the dust and gas are considered together, the composition was found to be by mass 45 per cent water, 28 per cent stony material and 27 per cent organic material. ESA named the mission after the artist Giotto di Bondone, who is thought to have used the 1301 appearance of Halley’s Comet as a model for the star of Bethlehem in his fresco, The Adoration of the Magi, painted in 1303 in the Scrovegni chapel in Padua. In 1992, Giotto was successfully reactivated after two years’ dormancy and seven years in space for an encounter with Comet 26P/Grigg-Skjellerup, a project known as the Giotto Extended Mission GEM.

English name for the constellation Camelopardalis.

A sudden change in the rotation rate of a pulsar. These are particularly prominent in the Vela Pulsar and the Crab Pulsar but many others also show them. In the Vela pulsar the jumps amount to 200 nanoseconds, which is twenty times larger than the steady decrease in period. Glitches are thought to be caused by starquakes.

A project under the auspices of the National Solar Observatory of the USA for the continuous monitoring of solar oscillations by a network of six observing stations spaced around the world at approximately 60° intervals in longitude. The instrument used, called a Fourier tachometer, is based on the Michelson interferometer. It measures small Doppler shifts of the spectral line of nickel at 676.8 nanometres, which is isolated by means of a Lyot filter. The whole disc of the Sun is focused at the same time on to an electronic detector composed of a matrix of 256 by 256 pixels. The Doppler shift at each pixel can be measured independently as a function of time. See also: helioseismology.

A roughly spherical, densely packed cluster of hundreds of thousands or even millions of stars. The brightest globular cluster in the sky is Omega Centauri ω Cen, which has a diameter of 620 light years. It is also one of the oldest globular clusters known, believed to be 15 billion years old. The globular clusters in our Galaxy contain some of its oldest stars. They are distributed within a spherical halo around the Galaxy, in contrast with open clusters, which are found only in the disc, and seem to move in highly elliptical orbits around the centre of the Galaxy. The stars in globular clusters contain low abundances of the elements heavier than helium. This is consistent with their having been formed from the original material of the Galaxy, before the composition of the interstellar medium had been enriched by elements made only inside stars. Globular clusters have also been recognized in other galaxies.

A small, almost spherical cloud of dark opaque gas and dust which shows up against a brighter background such as star clouds or a luminous nebula. It is thought that globules represent an early stage in the star formation process. The name of the Dutch-American astronomer, Bart Bok 1906-83, is associated with small globules, known as Bok globules, which may be only a few thousand astronomical units across.

Abbreviation for Greenwich Mean Astronomical Time.

Abbreviation for giant molecular cloud.

Abbreviation for Giant Metrewave Radio Telescope.

Abbreviation for Greenwich Mean Solar Time.

Abbreviation for Greenwich Mean Time.

A rod or plate mounted vertically to form a shadow-stick, such as that used on a sundial. The altitude of the Sun may be calculated from the height of the rod and the length of the shadow. The direction of the shadow gives the apparent solar time.

English name for the constellation Capricornus.