Why do countries have different time zones?

Answer 1

For every 15° of longitude you go west along the same latitude, sunrise, local noon and sunset are all one hour later. To keep local sunrise and sunset from getting too early or late, some countries that cover more than 15° of longitude use multiple time zones.

Answer 2

First, think of the time zones as they were first theoretically defined. There would be no funny bends and bumps as there are now. The zones would be defined by the lines of longitude starting at the Greenwich Meridian and going in 15 degree increments in either direction, all across the globe. Why 15 degrees? Because 24, the number of hours in a day, times 15 is equal to 360, and 360 degrees gets you all the way around the globe exactly once.

You have to have a time zone for each hour, because the hour is the largest commonly used division of time before you get to the day; there is no commonly used division of time in between hour and day. This turns out to be a very convenient and workable arrangement. Looking at the theoretical globe above, every hour of every day will be unfolding in its own time zone somewhere on the globe. When it is 8:15 AM in a zone, it will be 9:15 in the zone just to the east, and 10:15 to the zone to the east of that one.

On top of that, consider that there is no international law that dictates to any countries where the time zone lines will cross them. Each country everywhere is free to define their zones as they choose, or even if they want to follow the standard time zone system at all! So we have the familiar bends in the time zone boundaries, like the one to the west of Alaska. Some countries have decided to add regions where the time is off by some amount other than one hour; they are free to do this. Then there is the over-the-top stretch to the International Date Line made by the Pacific nation of Kiribati. (Actually this IDL shift is independent of time zone boundaries.)

So the time zones may seem chaotic, but in fact they represent a system that overall is very convenient and coherent. It did take me a while to get clear in my head the weirdness that happens at the International Date Line, but that is matter for another question. It is a most fortunate coincidence, or accident of history, that the International Date Line happens to fall on the globe where it causes confusion only for a small number of earthlings, all things considered.

Answer 3

Its because time is calculated with the help of latitudes and longitudes. one country can also have many time zones if its latitudes and longitudes are capable of creating them :)

-Hrijul Bhatnagar (The Known Scientist)

Answer 4

Because of the vast longitudinal area that they cover.

Answer 5

Because they cover a bigger area of the Earth's surface than smaller ones do, so their land mass will cross the time zones a lot more than smaller countries will.