Diurnal motion

The time for one complete rotation is 23 hours, 56 minutes, and 4.09 seconds – one sidereal day. The first experimental demonstration of this motion was conducted by Léon Foucault. Because Earth orbits the Sun once a year, the sidereal time at any given place and time will gain about four minutes against local civil time, every 24 hours, until, after a year has passed, one additional sidereal "day" has elapsed compared to the number of solar days that have gone by.

Relative direction

The relative direction of diurnal motion in the Northern Celestial Hemisphere are as follows:

• Facing north, below Polaris: rightward, or eastward
• Facing north, above Polaris: leftward, or westward
• Facing south: rightward, or westward

Thus, northern circumpolar stars move counter clockwise around Polaris, the north pole star.

At the North Pole, the cardinal directions do not apply to diurnal motion. Within the circumpolar circle, all the stars move simply rightward, or looking directly overhead, counterclockwise around the zenith, where Polaris is.

Southern Celestial Hemisphere observers are to replace north with south, left with right, and Polaris with Sigma Octantis, sometimes called the south pole star. The circumpolar stars move clockwise around Sigma Octantis. East and west are not interchanged.

As seen from the Equator, the two celestial poles are on the horizon due north and south, and the motion is counterclockwise (i.e. leftward) around Polaris and clockwise (i.e. rightward) around Sigma Octantis. All motion is westward, except for the two fixed points.