Expensive Planetarium is the star display written by Peter Samson for Spacewar!, one of the first interactive computer games. Conceived and written by Massachusetts Institute of Technology (MIT) students including Stephen Russell who programmed it, the Spacewar! game first ran in early 1962 on the PDP-1 donated to the school by Digital Equipment Corporation (DEC). The planetarium replaced the game's random dots of light in 1962 or 1963.
Samson encoded the night sky between 22½ degrees north and 22½ degrees south based on American Ephemeris and Nautical Almanac data. The planetarium displays all of the stars above fifth magnitude overCambridge, Massachusetts in their relative brightness. The stars can be fixed or can move from right to left.
Written in the PDP-1 assembler , the display got its name from the price of a PDP-1 at the time, about 120,000 in 1962 USD. Its predecessor Expensive Typewriter written by Stephen Piner and improved by Peter Deutschwas the editor which allowed the MIT users to operate the TX-0 and PDP-1 directly. Expensive Typewriter descended from Colossal Typewriter by John McCarthy and Roland Silver. Also during this period, Robert A. Wagner wrote the Expensive Desk Calculator, and David Gross created the Expensive Tape Recorder with help from Alan Kotok.
Nearly original Spacewar! can be played on the only functioning PDP-1, restored at the Computer History Museum in 2004–2006.