# eli5 Why do we have different time zones around the world, and how do they work?

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eli5 Why do we have different time zones around the world, and how do they work?

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Because the Earth is round and rotating, the Sun cannot shine on all surfaces of the globe at the same time. The time zones try to follow the Sun’s rays through the day and night cycle so that morning and night correspond to roughly similar clock times around the world.

The Earth is round, it rotates and only one side faces the sun at a time. There are twenty four time zones like bands around the earth, which chase the sun in steps of one hour to make sure that noon occurs approximately at 12:00 everywhere. Without zones people could have sunrise at arbitrary times like 23:00. Because we have learned to arrange our lives using clocks, and relying on daylight is important for energy savings and safety, clocks get adjusted to put daytime where we intuitively expect it to be.

So people have explained the scientific reason, but something a lot of people often bring up is “Why not just abolish them and have 1 standard time?”. Well, because it wouldn’t help.

You and someone in another country set up a meeting for 11am. Great, that’s easy, everyone has the same 11am. Oh, except for them, 11am is the middle of the night.

Because, you see, people would still have to live according to the sun. We can’t suddenly become nocturnal. So while everyone would use the same numbers, they’d have to shift their days to match.

Imagine you get off a plane in a foreign country. It’s dark out. Okay, but is it the evening, or is it early morning? You check the clock. 11am. Okay…still not helpful, since you have no idea what time of day this country’s 11am is. So is it early morning, or maybe early evening? You have no way of knowing.

Also, for people on a certain side of the world, this would mean 12am, midnight, now comes in the middle of the daytime. So you’d leave for work one day, come home the next day. Which would make things very confusing. If you’ve got a meeting “tomorrow”, does it mean the next work day, or this afternoon?

Time zones serve a very important purpose. They help us understand the world around us.

if we have same time all across the globe. then it wont make sense.
when in asia sun rises at lets say 6:00 am ,
sun rises on south america at 6:00 pm.

Because people want to use times that actually mean something to them. Historically the best reference point was when the sun was at its highest point in the sky (local noon) – and that worked fine for a long. But noon happens 4 minutes later for every degree you go west, so your noon probably isn’t mine. And once fast communication came along (notably the railways), having everyone using their own local time caused all sorts of problems. It made sense for countries to either use the same time everywhere, or split things up into well-defined zones.