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© Copyright 1999, Jim Loy
I you go by the sun, noon is when the sun is straight south. About 50 miles to the east, it was noon three minutes ago. 50 miles to the west, it is not noon, yet; it will be in three minutes. That is the time that you get from a sun dial that is properly aligned north/south. And that was the situation, until relatively recently.
In the 19th Century, railroads brought about time zones. To run trains on time, people needed to agree on what time it was. This is much easier if most of the local towns have exactly the same time.
Distant towns have a different time. Otherwise, the whole earth would have the same time. And then some places would have noon in the middle of the night.
So the world was divided into 24 time zones. Each zone is one hour different from those adjacent to it. On the oceans, the borders between zones run mostly north and south. On land, these borders follow political boundaries, nation and state boundaries. This makes it handier for the local people. Alaska (including the Aleutian Islands) is all one time zone, even though it would appear to span four time zones.
On land, the time zone boundaries zig zag, quite a bit. In Siberia, there are time zones, adjacent to each other, which have 2-hour differences.
There are a few places that use a fractional time zone. India, spanning two time zones, has chosen a time midway between the two times. When it is noon in London, it is 5:30 PM in India. The central part of Australia is also a fractional time zone.
See Daylight Savings Time and International Date Line. I hope to have a map on this page, eventually.