On Salisbury Plain, 75 miles southwest of London, Stonehenge was built in three phases, beginning in 2800 B.C. by Neolithic people and culminating around 1800 B.C. during the Bronze Age. It evolved into primarily a 100-foot circle of 29½ sarsen stones, each standing 14 feet high and weighing 25 tons, capped by seven-ton stone lintels, with five trilithons inside the circle whose vertical stones stood 25 feet tall and weighed over 52 tons. Its construction in an age 4,000 years in the past made it an outstanding engineering project, and it was oriented so the rising sun at the summer solstice could be observed through the central trilithon aligned with the heel stone outside the ring. The same alignment also could be used to observe the mid-winter full moon rise and to determine whether a lunar eclipse was imminent, and the sarsen stones are believed to have represented the 29½ days of the lunar month. Provision has also been made in UM-Rolla Stonehenge to use an analemma to indicate the date and time shown by the noon sun, a type of observation used by the Anasazi Indians in Chaco Canyon, New Mexico, from 950-1150 A.D. to maintain their calendar and observe lunar phenomena, and further provisions allow Polaris, the North Star, to be located and observed during the hours of darkness. This half-scale model incorporates many features of the original, but its rock was formed with modern versions of ancient practices, using high-pressure water-cutting technology at 15,000 PSI to cut the stone to its present shapes within a month's work, and southwest of its heel stone stands a simulation of an ancient computer near a modern computer facility.
