Question

why do we see on side of moon always

Answer 1

- because the moon does not rotate (i.e. spin on its own axis) like the earth does. Because it does not rotate we only see the side that faces us and this side faces us all the time.Try this.Tie a length of string to a ball and swing it round your head - what do you see when you look at the ball.You see the same side of the ball all the time. Is the ball rotating (i.e. spinning on its own axis) - well no it isn't.This is exactly like the moon orbiting the earth; the gravitational force between the earth and the moon acts like the string and the moon doesn't rotate about its own axis, just like the ball on the end of the string doesn't.

Answer 2

The near side of the Moon is the lunarhemisphere that is permanently turned towards the Earth, whereas the opposite side is the far side of the Moon. Only one side of the Moon is visible from Earth because the Moon rotates on its axis at the same rate that the Moon orbits the Earth, a situation known as synchronous rotation or tidal locking. The Moon is directly illuminated by the Sun, and the cyclically varying viewing conditions cause the lunar phases. The unilluminated portions of the Moon can sometimes be dimly seen as a result of earthshine, which is sunlight reflected off the surface of the Earth and onto the Moon. Since the Moon's orbit is both somewhat elliptical, and inclined to its equatorial plane, libration allows up to 59% of the Moon's surface to be viewed from Earth (but only half at any instant from any point).