observation.wheel.london.eye.arp.750pix.jpg|thumb|right|250px|The British Airways London Eye observation wheel on the banks of the River Thames near the Houses of Parliament, London, England]]

An observation wheel is a large slowly-rotating vertically-oriented nonbuilding structure carrying enclosed passenger cars or pods along its circumference. Although observation wheels are often described as Ferris wheels, the two differ in a number of significant respects:

• Ferris wheels often have open cars or, in small wheels, individual bucket seats. An observation wheel has completely enclosed cars.

• A Ferris wheel's passenger cars hang within the wheel's frame and are usually kept level by gravity. An observation wheel's cars are mounted on the outside of the frame and are stabilised mechanically.

• A Ferris wheel is supported by two towers on each side of the axle. An observation wheel is supported by a single A-frame mounted on one side.

The world's most famous observation wheel is the London Eye in London, England, operated by British Airways. Its great popularity has led to a number of other cities, including Birmingham and York (United Kingdom), Moscow (Russia), Las Vegas (United States), Shanghai (China), Melbourne (Australia) and Singapore proposing to erect similar wheels. The proposed Birmingham wheel would perhaps be the most unusual, as it would be fixed in place while the pods would move around the circumference along a rail track. Las Vegas and Singapore are competing to build the highest in the world, at 182 m (597 ft) and 178 m (584 ft) respectively. While the wheel in Las Vegas is projected to open in late 2005, the Singapore Flyer had its completion date postponed to 2008. The Shanghai Star, initially planned as a 200 m (656 ft) tall wheel to be built by 2005, was revised to 170 m with a completion date set in 2007. The proposed 120 m (394 ft) tall Southern Star Observation Wheel is expected to open in Melbourne in 2008.

See also

• Ferris wheel
• London Eye

Amusement rides