Nowadays, the Earth's rotation is measured and reported thanks to radio telescopes and VLBI observing distant objects in the universe. Values are tabulated for each 0h UTC every day in the IERS publications, allowing to derive the angle that Earth has rotated every 86,400 SI seconds, allowing to scientifically monitor variations in Earth's rotation compared to a very constant unit of time realized by atomic clocks. If you want to know the amount of Earth rotation for every SI day, you're in luck: it is possible to consult reports of the Earth's orientation (rotation and polar motion) thanks to the IERS. Rounded to one decimal place, this gives you 361.0°, a figure that will likely remain true for at least several millenia. So this is more a modern approximation rather than an exact value.

However, the Earth's rotation and revolution are not constant, and are always changing at somewhat unpredictable rates, so the angle is not perfect, but the changes are very slow. So according to this formula, a (UT1) day is 1.00273781191135448 Earth rotations, which multiplied by 360° is about 360.98561°. Where $Tu$ is the Julian UT1 Date - 2451545.0 The current formula linking the Earth Rotation Angle (ERA) to the modern approximation of mean solar time, UT1 (basically the Earth's clock following the mean day/night cycle), is by definition : To get a more averaged value, let's use the mean solar day. Since we generally refer to the traditional day/night cycle when we say 'day', this means a form of solar time. SI day: a unit of time containing exactly 86,400 SI seconds defined by caesium atoms. Stellar/Sidereal day: the time needed for the Earth to rotate once relative to the stars Mean solar day: a more uniform, averaged solar day without seasonal variations There are several types of days:Īpparent solar day: the time between two successive culminations of the Sun (apparent Noon) from an fixed Earth-based observer First, we need to decide which definition of 'day' to employ.

Earth 360 degree view