D layer

A category of dark grey asteroids with albedos of about 5 per cent. The C is for carbonaceous, and they are believed to consist of the same type of material as the carbonaceous chondrite class of meteorites. C-type asteroids are common in the outer part of the main belt.

A small, insignificant southern constellation, introduced by Nicolas L. de Lacaille in the mid-eighteenth century with the longer name Caela Sculptoris. It has no star brighter than fourth magnitude.

Location in southern Spain of an observatory constructed by the Max-Planck-Institut für Astronomie and operated jointly with the Spanish National Commission for Astronomy. The telescopes are 1.2-metre 4-foot, 2.2-metre 7-foot and 3.5-metre 11.5-foot reflectors, together with a 0.8-metre 2.5-foot Schmidt camera. A 1.5-metre5-foot telescope operated by the University of Madrid is also at the site.

A large volcanic crater, usually more than two kilometres in diameter. Calderas are created by collapse or explosive eruption, or a combination of the two, and often have a complex structure.

A year containing 365 or 366 whole days according to whether the year is a leap year or not in the Gregorian calendar.

A non-profit organization formed as a collaboration between the California Institute of Technology and the University of California with the purpose of building and operating the Keck Observatories in Hawaii.

A bright gaseous emission nebula in the constellation Perseus, named for its resemblance to the shape of the US state. It forms the rim of a dark nebula of gas and dust illuminated by the star Xi ξ Persei.

One of the four large Galilean moons of Jupiter number IV, discovered in 1610. It is the darkest of the Galilean satellites and also the least dense, which suggests that it contains a high proportion of water, though detailed surface images returned by Galileo indicate that the surface at least may contain more rock and dust than previously supposed. by Voyager and Galileo images show that the surface is heavily cratered but has little relief. The most prominent surface feature is a multi-ring structure called Valhalla, which consists of a central bright zone 600 kilometres 375 miles across, surrounded by numerous concentric rings spaced at intervals of 20 to 100 kilometres 12 to 60 miles. At least seven other multi-ring features have been recognized.

A large, multi-ringed, impact basin on Mercury. It is 1,300 kilometres 800 miles in diameter and the most conspicuous feature on the planet.

submillimetre wave astronomy.

A small satellite of Saturn discovered in 1980. It is co-orbital with Tethys and Telesto.

A large but inconspicuous constellation occupying a sparse region of the sky near the north celestial pole. It was first recorded in 1624 by the German mathematician Jakob Bartsch, a son-in-law of Johannes Kepler.

Asteroid 107, diameter 236 km, discovered in 1868 by N. Pogson.

A 3.6-metre 140-inch telescope at the Mauna Kea Observatories in Hawaii. Commissioned in 1979, it is a major facility for French and Canadian astronomers also used by the University of Hawaii. Its versatile design and location make it suitable for both optical and infrared observations.