The period before sunrise and after sunset when the sky is partially illuminated by scattered sunlight. Civil twilight is defined as the period when the zenith distance of the centre of the Sun's disc is between 90° 50' and 96°; nautical twilight is the interval when it is between 96° and 102°, and astronomical twilight that when it is between 102° and 108°.

English name for the constellation Gemini.

A graph on which two colour indices such as B-V and U-B are plotted, one along each axis, for a sample of stars or other objects, such as asteroids. See also: UBV photometry.

A prominent lunar crater in the Moon’s southern uplands. It is surrounded by the brightest and most extensive ray system on the Moon, possibly indicating that it is one of the youngest major features. The terraced walls rise to a height of 4.5 km and the central peak to 2.3 km above the floor of the crater, which is 85 km 53 miles in diameter.

A supernova in the constellation Cassiopeia observed by Tycho Brahe in 1572. At maximum brightness it rivalled Venus and was visible in daylight. The supernova remnant is both an X-ray source and an intense source of radio emission; the expanding shell of gas is faintly visible with powerful optical telescopes.

The nearest town to the Baikonur space centre in Kazakhstan.