Earth completes one full rotation around its axis approximately every 24 hours relative to the Sun, which defines the length of a mean solar day

. More precisely, the rotation period relative to distant stars (a sidereal day) is about 23 hours, 56 minutes, and 4 seconds

. This difference arises because Earth is also orbiting the Sun, so it must rotate a little more than one full turn relative to the stars to complete a solar day. In summary:

• One rotation relative to the Sun (mean solar day): about 24 hours
• One rotation relative to distant stars (sidereal day): about 23 hours 56 minutes 4 seconds

This rotation period is not perfectly constant; it is gradually slowing down over centuries due to tidal interactions with the Moon, lengthening the day by roughly 1.7 milliseconds per century

. However, recent observations indicate that Earth's rotation has temporarily sped up slightly