A large southern constellation, which is one of the four parts into which Nicolas L. de Lacaille divided the ancient constellation Argo Navis. It lies in part of the Milky Way rich with faint nebulosity and contains ten stars brighter than fourth magnitude. The stars Delta δ and Kappa κ, together with Iota ι and Epsilon ε Carinae, make an asterism known as the false cross since it is sometimes confused with the constellation Crux, the true Southern Cross.

A pulsar in the constellation Vela, associated with a supernova remnant 10,000 years old. It is one of the strongest radio pulsars, and the strongest gamma-ray source in the sky. It was discovered in 1968 during a general search for pulsars in the southern hemisphere and has a short period, 89 milliseconds, characteristic of young pulsars. The period is steadily increasing at a rate of 10.7 nanoseconds a day as the pulsar loses energy. Since observations of it started, the pulsar has also undergone several major glitches in which the period has suddenly decreased by about 200 nanoseconds.

A series of Soviet spacecraft sent to explore the planet Venus. The first to land successfully was Venera 7 in 1970. There have been nine further Venera probes producing images of the surface of Venus, and data about the atmosphere and the composition of the planet’s crust.

The second major planet of the solar system, in order from the Sun. It is one of the terrestrial planets, similar in nature to Earth and only slightly smaller. Like the Earth, it is surrounded by a substantial atmosphere. Venus can come closer to the Earth than any other planet and can be the brightest object in the sky apart from the Sun and Moon. Because its orbit lies inside the Earth’s, its position in the sky can never be further than 47° away from the Sun. As a result, Venus can be viewed either in the western sky in the evening, or in the eastern sky in the morning. It is sometimes called the morning star or the evening star. As a further consequence of its location within the Earth’s orbit, Venus appears to go through a cycle of phases similar to the Moon’s. At its brightest and nearest, even a small telescope will show that Venus is actually a crescent. The surface is perpetually covered by dense, highly reflecting clouds which show few features in visible light, though ultraviolet photographs reveal a banded structure, including a characteristic Y-shaped feature. These clouds consist of droplets of dilute sulphuric acid, created by the action of sunlight on the carbon dioxide, sulphur compounds and water vapour present in the atmosphere. The atmosphere is almost entirely of carbon dioxide, and the surface pressure is more than 90 times that at the surface of the Earth. The exceptionally high surface temperature of 730 K 450°C is a result of the greenhouse effect. Venus was the target of a large number of Soviet and American probes in the 1970s and 1980s, notably the Soviet Venera and Vega series and the American Pioneer Venus. The extremely high temperature and pressure present considerable difficulties and many of the probes were destroyed either before returning data or after a relatively short period of operation. Nevertheless, it proved possible to analyse the chemical composition of some surface rocks and to return limited panoramic views of the surface terrain, showing rocky desert landscapes. The first radar maps produced by spacecraft orbiting the planet showed that most of the surface consists of vast plains, above which several large plateaux rise to heights of several kilometres. The two main highland areas are Ishtar Terra in the northern hemisphere and Aphrodite Terra in the equatorial region. The Maxwell Montes are the highest feature, rising to 11 kilometres above the mean level of the planetary surface. In 1990, the US Magellan probe arrived in orbit around Venus and commenced a programme of mapping the surface in much greater detail than had been achieved previously, by means of sophisticated radar techniques. Ample evidence has been found of both impact features and volcanic activity in the relatively recent past. By solar system standards, the surface of Venus is young: the oldest craters appear to date from 800 million years ago. However, no evidence has yet been found of current volcanism. The thick atmosphere and high surface temperature mean that impact craters take forms rather different from those on other planets and satellites. Smaller meteorites burn up readily on passing through the atmosphere so there is an absence of smaller craters. The material thrown out in the powerful impacts of larger meteorites did not travel far and tended to spread round the craters in molten form. Large numbers of volcanic features have been identified: lava flows, small domes 2-3 kilometres across, larger volcanic cones hundreds of kilometres across, coronae and so-called arachnoids. The coronae of Venus are circular or oval volcanic structures surrounded by ridges, grooves and radial lines. They appear to be collapsed volcanic domes and are different from any features seen on other planets or satellites. The arachnoids, which get their informal name from their spider-like appearance, are similar in form to coronae, but generally smaller. According to one theory, arachnoids may be precursors to coronae. The bright lines extending outwards for many kilometres indicate formations that may have been created when magma upwelled from the planet’s interior, causing the surface to crack.

equinox.

A radio telescope consisting of 27 dishes, each 25 metres (82 feet) in diameter, configured to carry out Earth rotation synthesis. Located at Socorro, New Mexico, it is the world's largest aperture synthesis telescope. It elements are arranged in a Y-shape with three arms each 21 kilometres (13 miles) long. The dishes are connected electronically so as to be equivalent to 351 radio interferometers observing simultaneously. The maximum resolution obtainable is 0.05 arc seconds at a wavelength of 1.3 centimetres, although in practice most observations are made at 6 centimetres with 1 arc second resolution as this greatly reduces the time needed to construct a radio map.

The European Southern Observatory’s set of four, linked 8-metre 300-inch telescopes located at Paranal Observatory in Chile. The light-gathering power of the four telescopes together is equivalent to that of a mirror 16 metres 52 feet in diameter. Construction work began in late 1988. The first telescope was finished in 1997 and final completion of all four is scheduled for 2001. The technology employed is the same as for the New Technology Telescope.

A network of radio telescopes in North America for very-long-baseline interferometry. It consists of ten antennas, distributed from Hawaii to St Croix in north-east Canada. The effective diameter is 8,000 kilometres 5,000 miles and the resolution attainable 0.2 milliseconds of arc.

A technique in radio astronomy that effectively creates a radio interferometer in which the component antennas are separated by very large distances, typically thousands of kilometres. The antennas are not connected electrically or through microwave links. Instead, video signals are registered on magnetic tape, together with very accurate timings, at each observing station. The tapes from each station are brought together later and played through a radio receiver to complete the analysis. The technique provides extremely accurate positions for radio sources, resolutions but not maps down to a few milliseconds of arc and the direct detection of continental drift. Antenna separations even greater than the Earth’s diameter can be achieved by placing radio telescopes in orbit and using them in conjunction with ground-based telescopes. The launch of the Japanese satellite, HALCA originally known as Muses-B, in February 1997 marked the first stage in the development of the international VSOP - the VLBI Space Observatory Programme. HALCA, an umbrella-shaped antenna 8 metres 26 feet in diameter, was placed in an elliptical orbit, providing a baseline up to three times larger than the Earth.

Asteroid 4, diameter 576 km, discovered by H. W. M. Olbers in 1802. It is the third-largest asteroid known and the brightest of all, sometimes reaching a visual magnitude of 6, when it is just detectable to the unaided eye under optimum observing conditions. Vesta’s brightness is due to its high albedo of 25 per cent. As it rotates every 5.43 hours, regular changes in the colour and spectrum are observed, reflecting the fact that the surface is not uniform. Vesta appears to be a true mini-planet which has survived largely intact since the solar system formed, rather than being a fragment from a larger body. Hubble Space Telescope images reveal details down to 80 km 50 miles across, including impact craters. One large crater seems to have torn away part of the crust completely, exposing the mantle below. There is evidence for ancient lava flows dating from 4 billion years ago when the interior was hot and molten. It is thought that Vesta may be the parent body of the eucrite type of meteorites.

A 4-metre 160-inch telescope at the Cerro Tololo Inter-American Observatory.

The uneven illumination of the image plane in an optical instrument such as a telescope. The usual cause of vignetting is obstruction of the light by parts of the instrument itself.

Two identical American probes sent to the planet Mars in 1975. Both Vikings 1 and 2 consisted of an orbiter, which remained circling the planet, and a soft lander. Viking 1 was launched on 9 September 1975 and reached Mars orbit on 19 June 1976. Images were taken to locate a suitable landing site and the landing took place on Chryse Planitia on 20 July 1976. The orbiter’s path was adjusted several times in order to obtain close-up images of Mars satellites, Deimos and Phobos, and to observe different aspects of the martian surface. Viking 2 was launched on 20 August 1975 and reached Mars orbit on 7 August 1976. The landing took place on Utopia Planitia on 3 September 1976. The orbiters were equipped with two television cameras, an infrared spectrometer to map the distribution of water vapour and a radiometer for determining temperature distribution. The landers sampled the upper atmosphere during descent, made meteorological measurements and carried out experiments on samples of martian soil. One of the prime objectives was to test for the presence of organic material which might indicate the existence of life, but nothing incontrovertible was found. Thousands of images were returned from both the orbiters and landers. The whole of the martian surface was mapped to a resolution of 150-300 metres. The Viking 1 orbiter operated until 7 August 1980, and the Viking 2 orbiter until 25 July 1978. The landers ceased operating in November 1982 and February 1980, respectively. The mission was regarded as very successful, and it had greatly exceeded its expected lifetime.

English name for the constellation Virgo.

A zodiacal constellation and the second-largest in the sky. It is one of the 48 constellations listed by Ptolemy c. AD 140. The brightest star is the first magnitude Spica, and there are seven others brighter than fourth magnitude. The constellation contains the rich and relatively nearby Virgo Cluster of galaxies. Eleven of the brighter galaxies are listed in the Messier Catalogue.