Why are the rate of earth rotation 24hours and its axis tilted by 23.5 degree with respect to its orbit?

Answer 1

While most studies have discussed the rotation rate of a planet on the basically same kind of model where spin angular momentum of a planet was accreted from a disk of planetesimals at the early stage of planet formations, an article posted recently proves that the earth rotation rate can be derived by an almost exact number from the fundamental quantities of the earth and moon system just as the period of orbital motion can be derived from their fundamental quantities.

The rotation axis of the earth and the rotation rate of the sun in its equator can also be derived from the same theoretical basis.

The article describes
"As the earth acts a torque to rotate the moon synchronously to the orbital motion, there should be a reaction torque on the earth. It is demonstrated that the earth spin is driven by the force of the reaction torque, which leads the earth spin to be calculated from the fundamental quantities of the earth-moon system by almost an exact number, 23h38m58s without taking into account the density distribution, 24h3m15s and 23h52m26s with taking into account the density distribution. It is also demonstrated that the earth spin axis which is tilted by 23.5 with respect to the earth orbit can be derived from the gravitation of the sun acting on the earth. The calculated number, 23.487degree, is astonishingly close to the observation. The spin of the sun is also obtained by the same way as the earth by reducing the many body system into a two body system. The calculation results in an approximated number which validates our theory, analysis, and calculations".

Refer to the website at Google blog: EarthRotation, "http://earthrotation.blogspot.com/"

Answer 2

In fact the earth does not rotate in 24 hours. As the earth rotates it is also orbiting the sun in an elliptical path. If we were to take the Greenwich Meridian as an example; at midday the sun is directly over that meridian, however 24 hours later the earth has moved around its path relative to the sun and so the sun is no longer over the Greenwich Meridian. This means that the length of a day will vary depending on where the earth is in its solar orbit. In fact it will vary throughout the year by about 16 minutes. This would be very inconvenient as a time standard and so the 24 hour day was used as a mean of these differing times. Hence the term "Mean Time".

There is,therefore, a difference between "mean time" and "apparent(or real) time". This is known as the "equation of time".

As far as the inclination of the earth's axis to its plane of rotation is concerned, there is no apparent reason for this. However this inclination is the cause of the seasons as the apparent path of the sun travels from the Tropic of Cancer to the Tropic of Capricorn and back.

Answer 3

Because of the way we define hours and degrees.

Doug