Kitt Peak National Observatory, Tuscon, Arizona, USA, at night. With 23 telescopes, this is the largest collection of astronomical instruments in the world. From left to right the telescopes seen here are: the Spacewatch 1.8-meter telescope, the Spacewatch 0.9-metre telescope, the Bok 2.3-metre telescope (operated by the Steward Observatory, University of Arizona) and the Mayall 4-metre telescope.