how long does the earth take to complete one round of rotation
Earth's rotation Earth rotates once in about 24 hours with respect to the Sun, but once every 23 hours, 56 minutes, and 4 seconds with respect to the stars (see below). Earth's rotation is slowing slightly with time; thus, a day was shorter in the past. This is due to the tidal effects the Moon has on Earth's rotation. Atomic clocks show that a modern day is longer by about 1.7 milliseconds than a century ago,[1] slowly increasing the rate at which UTC is adjusted by leap seconds. Analysis of historical astronomical records shows a slowing trend of about 2.3 milliseconds per century since the 8th century BCE.[2]
Diurnal motion Diurnal motion (Latin: diurnus, lit. 'daily', from dies, lit. "day") is an astronomical term referring to the apparent daily motion of stars around Earth, or more precisely around the two celestial poles. It is caused by the Earth's rotation around its axis, so almost every star appears to move along a circular arc path 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 conducted by Léon Foucault.