Universal Time is a time standard based on Earth's rotation. While originally it was mean solar time at 0° longitude, precise measurements of the Sun are difficult. Therefore, UT1 is computed from a measure of the Earth's angle with respect to the International Celestial Reference Frame (ICRF), called the Earth Rotation Angle. UT1 is the same everywhere on Earth. UT1 is required to follow the relationshipERA = 2π(0.7790572732640 + 1.00273781191135448 · Tu) radians
An 1853 "Universal Dial Plate" showing the relative times of "all nations" before the adoption of universal time
Earth's rotation or Earth's spin is the rotation of planet Earth around its own axis, as well as changes in the orientation of the rotation axis in space. Earth rotates eastward, in prograde motion. As viewed from the northern polar star Polaris, Earth turns counterclockwise.
This long-exposure photo of the northern night sky above the Nepali Himalayas shows the apparent paths of the stars as Earth rotates.
Starry circles arc around the south celestial pole, seen overhead at ESO's La Silla Observatory.
An artist's rendering of the protoplanetary disk