Gemini

Prominent zodiacal constellation in the northern hemisphere represented as the twins Castor and Pollux. Its brightest star is Pollux; Castor is a system of six stars. The Sun passes through Gemini from late June to late July. Each December, the Geminid meteors are seen, their trails giving the appearance of radiating from Gemini. In astrology, the dates for Gemini are between about 21 May and 21 June (see precession).

Gemini

Pair of 8-m/26-ft astronomical telescopes on high mountain sites in Hawaii and Chile. Each telescope has a primary mirror 8 m/26 ft in diameter and 20 cm/8 in thick, constructed of ultra low-expansion glass. The shape of the mirror is adjusted by 120 active supports to prevent it sagging as the telescope moves across the sky. A system of adaptive optics compensates for the distorting effects of the atmosphere, producing sharp images throughout the visual and near-infrared parts of the spectrum.

The two sites, Gemini North at Mauna Kea, Hawaii (4,200 m/13,784 ft high) and Gemini South at Cerro Pachón, Chile (2,700 m/8,858 ft), have excellent observing conditions and, between them, cover the whole sky. The $176 million project is funded by the USA, UK, Canada, Chile, Argentina, and Brazil. Gemini North became operational in 1999, and Gemini South in 2002.