A compass is any magnetically sensitive device capable of indicating the direction of the magnetic north of a planet's magnetosphere. The face of the compass generally highlights the cardinal points of north, south, east and west. Often, compasses are built as a stand alone sealed instrument with a magnetised bar or needle turning freely upon a pivot, or moving in a fluid, thus able to point in a northerly and southerly direction. The compass was invented in ancient China some time before the 2nd century and was used for navigation by the 11th century.
