Question

Statement I : Sideral day is shorter than Solar day. 

Statement II : The motion of the Earth in its orbit around the Sun is termed as revolution. 

 (a) Both the statements are individually true and 

Statement II is the correct explanation of Statement I 

(b) Both the statements are individually true but 

Statement II is not the correct explanation of Statement I

(c) Statement I is true but Statement II is false 

(d) Statement I is false but Statement II is true

Answer 1

(b) The sidereal day is the time it takes for the Earth to complete one rotation about its axis with respect to the ‘fixed’ stars. By fixed, we mean that we treat the stars as if they were attached to an imaginary celestial sphere at a very large distance from the Earth. A measurement of the sidereal day is made by noting the time at which a particular star passes the celestial meridian (i.e. directly overhead) on two successive nights. On Earth, a sidereal day lasts for 23 hours 56 minutes 4.091 seconds, which is slightly shorter than the solar day measured from noon to noon. At the same time that the Earth spins on its axis, it also orbits or revolves around the Sun. This movement is called revolution.