A popular name for the Pleiades star cluster.

A faint constellation of the southern hemisphere introduced in the late seventeenth century by Johannes Hevelius, supposedly to commemorate the instrument he used to make astronomical observations. Its brightest star is magnitude 4.5.

English name for the constellation Sextans.

A type of galaxy with a brilliant point-like nucleus and inconspicuous spiral arms, first described by Carl Seyfert in 1943. The spectrum shows broad emission lines. About 1 per cent of spiral galaxies are Seyferts. Many are comparatively strong infrared sources; in some the central core is a weak radio source. Brightness variations in the nucleus are common.

A group of apparently interacting galaxies in the constellation Serpens. It consists of five galaxies, together with a large cloud of gas ejected by the principal galaxy in the group. This galaxy, which is a spiral, and three lenticular galaxies in the group are interacting gravitationally and lie at a distance of 260 million light years. The fifth galaxy is a spiral five times further away, coincidentally lying in the same part of the sky.

A phenomenon sometimes observed briefly just before and just after totality in the course of a total solar eclipse. Irregular bands of shadow, a few centimetres wide and up to a metre apart, are seen to move over the ground. The mechanism is not fully understood but may involve refraction in the atmosphere of the light from the thin crescent of the Sun. They are seen only if the sky is very clear.

A catalogue of 1,249 galaxies brighter than thirteenth magnitude, prepared from a photographic survey undertaken between 1930 and 1932 at Harvard College Observatory. It was published in the Annals of the Observatory, as volume 88 part 2.

The second-brightest star in the constellation Scorpius, marking the Scorpion’s sting. It is a B star of magnitude 1.6.

A B star with a characteristic spectrum in which sharp absorption lines, flanked by emission wings, are superimposed on a normal spectrum of broad absorption lines. The spectrum can be explained by the presence of a ring of circumstellar material, probably created as a result of the star’s rapid rotation. Pleione in the Pleiades is an example.

A research institute of the Academy of Sciences of Azerbaijan, established in the 1960s. It is located 22 kilometres 14 miles from the village of Shemakha, at a height of 1,400 metres 4,600 feet in the Caucasus. The main instrument is a 2-metre 80-inch reflector.

Natural planetary satellites, often in pairs, whose gravitational influence appears to hold a planetary ring in place, preventing it from dispersing. Prometheus and Pandora are the shepherd satellites for the F-ring of Saturn.

A type of stony meteorite, consisting of basalt-like rock. Together with nakhlites and chassignites, shergottites belong to the class of SNC meteorites, believed to have originated on the surface of Mars. The name is derived from Shergotty in India where such a meteorite fell.

English name for the constellation Scutum.

A large volcano with gently sloping sides, built up from successive lava flows from a single vent. Individual layers may amount to only a few metres but they can build up to create a very high mountain. Typically, the slope of the sides is under 10°. At the top is found a large, shallow, flat-floored crater called a caldera.

English name for the obsolete constellation Argo Navis.