(rail transport) A railway passenger car made so as to facilitate seeing the scenery en route, sometimes with glass sides or with a kind of open balcony at the rear.

plural of observable universe

(astronomy) The extent of a universe within the cosmological horizon of an observer.

Ferris wheel

plural of observation wheel

(statistics) The difference between a measured value of a quantity and its true value.

plural of observational error

(military) A type of balloon that is employed as an aerial platform for intelligence gathering and artillery spotting.

The situation in which a phenomenon being observed for study is unwittingly influenced by the presence of the observer.

A rudimentary building used by people making field observations.