Universe Today
Solar vs. Sidereal Day:
The amount of time it takes for the Sun to return to the same spot in the sky is called a solar day, which is 24 hours. However, this varies through the year, and the accumulated effect produces seasonal deviations of up to 16 minutes from the average. This is caused by two factors, which include the Earth's elliptical orbit around the Sun and it's axial tilt.
Orbit and Axial Tilt:
Rotational Velocity:
However, the planet is slowing slightly with the passage of time, 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, slowly increasing the rate at which UTC is adjusted by leap seconds. The Earth's rotation also goes from the west towards east, which is why the Sun rises in the east and sets in the west.
