Diurnal motion is an
astronomical term referring to the apparent daily
motion of
stars around the
Earth, or more precisely around the two
celestial poles. It is caused by the Earth's rotation on its axis, so every star apparently moves on a circle, that is called the
diurnal circle. The time for one complete rotation is 23 hours, 56 minutes and 4.09 seconds (
1 sidereal day). The first experimental demonstration of this motion was undertaken by
Léon Foucault.