What is the significance of the int. date line? why would you turn your calendar forward or backward?

Question

What is the significance of the int. date line? why would you turn your calendar forward or backward?

Answer 1

In the beginning, the day has to start somewhere specific since the sun can't shine everywhere at the same time so scientists got together and decided the middle of the pacific ocean where nobody lived would be a good place to start the day, as the sun then goes around the day the time of day follows the sun around the earth, all 24 hours, you cross the international date line you are either going into tomorrow or coming back to yesterday.  Did you get all that.

Answer 2

The reason is that the earth is round and at any one time the sun is only shining on one half of the earth and the other half is in darkness. Therefore the half of the earth that is in sun-shine is  morning of a certain date and the other half that is in darkness is the night before. If the whole world had morning/night at the same time (ie if the earth was flat) there would be no need for the IDL