Question

The local time is decided by the noon time.

Answer 1

The local time is decided by the noontime with the help of the direction of the sun.

The sun will always point the shadow in the north direction at the high moon.

However, during the night time, it becomes difficult to determine the time as there were no sun or shadow to point at.

Answer 2

(1) When at particular place the sun reaches the maximum height in the sky it is assumed that almost half of the day time is over and this time is considered 12 noon.

(2) The time of particular place as decided by the overhead position of the sun in the sky in considered as the local time of that place.

(3) During the rotation of the earth, when a particular longitude comes exactly in front of the sun, it is considered as noon time (12 noon) on that longitude. This noon is considered as local time of that longitude.

THIS IS THE GEOGRAPHICAL REASON OF YOUR QUESTION !