Question

How much time does it take for the Earth to revolve around itself?
(A) $365$ days
(B) $24$ hours
(C) $30$ hours
(D) $4$ weeks

Answer 1

Hint: To answer this question, we have to identify the motion of the earth in the given revolution. Then, analysing this motion with respect to the sun, we can easily determine the required time.

Complete step by step solution:
The revolution of the earth around itself is nothing but the time that the earth takes to rotate about its own axis. So, as we can imagine, in the first half of the time period, the half of the surface of the earth will face the sun, and in the next half of the time period, the other half of the surface of the earth will face the sun. Hence, for each half of the surface of the earth, in this full time period, one full day and one full night will be elapsed. This will be true for each part of the earth. Hence, we can say that the time that the earth takes to revolve around itself is equal to the time elapsed in one full day of the earth.
As we know that there are a total of $23$ hours, $56$ minutes, and $4$ seconds. This is approximately taken to be equal to $24$ hours.

Hence, the correct answer is option (B).

Note:
The time discussed in this question is known as the sidereal time. The sidereal time is measured with respect to the stars in the space, not with respect to the sun. The value of this time is very much helpful for the astronomers. They are able to predict where the earth is in its orbit using this value, so that they are able to point their telescopes in the correct position.
The difference in the approximate value and the actual value of this time is due to the fact that, in this time period, the earth not only rotates about its axis, but also it moves along its orbit. So, at the end of the rotation, the sun does not appear at the same position, as it was at the beginning of the rotation. So the earth has to spin for extra four minutes to face the sun at the same position.