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Foundations
Time Zones and the International Date Line
Right now it is two different days on Earth at the same moment. Someone is finishing Tuesday while someone else has already started Wednesday. That strange fact falls straight out of a round, spinning planet, and once you see how it works, time zones stop being a travel nuisance and become another way to read the map.
Longitude becomes time
The Earth turns a full 360 degrees in 24 hours, which works out to 15 degrees every hour. So the globe is sliced into roughly 24 time zones, each about 15 degrees of longitude wide, counted as offsets from Coordinated Universal Time (UTC), the modern successor to Greenwich Mean Time. Move east and clocks run ahead; move west and they fall behind. Your longitude, in other words, is really just your time of day in disguise.
Why the zones are not tidy stripes
In practice the lines bend to follow national borders, because a country prefers to keep one clock. Some sprawling nations embrace many zones: Russia runs across eleven. Others insist on a single one despite their width, which is why all of China uses one time even though it stretches across what would naturally be five zones. When a clue mentions a country spanning many time zones, it is telling you the place is very wide east to west.
The date line, and where the day begins
Follow the zones around the world and eventually east meets west, and the two must differ by a full day. That seam is the International Date Line, running roughly along the 180-degree meridian in the Pacific. It zigzags hard to keep island nations on a single date. Kiribati redrew it in 1995 so all of its islands would share one day, which nudged its easternmost islands to the very front of the world's clock. They are among the first places on Earth to greet each new day. A clue about "the first place to see the sunrise of the new year" is pointing at that corner of the Pacific.
Bottom Line
Time zones turn longitude into clock time at fifteen degrees an hour, bending to fit borders, and the International Date Line marks where one calendar day hands off to the next. Read a clue's hints about time and width, and you have another axis for pinning a place east to west.
Frequently Asked Questions
Why does the Earth have 24 time zones?
The Earth turns 360 degrees in 24 hours, or 15 degrees per hour, so it is divided into about 24 zones of roughly 15 degrees of longitude each, measured as offsets from UTC.
What is the International Date Line?
It is an imaginary line running roughly along the 180-degree meridian in the Pacific where the calendar date changes by a day. It zigzags to keep island nations on a single date.
Which country has the most time zones?
Among contiguous nations, Russia spans eleven time zones. Counting overseas territories, France covers the most in total. By contrast, all of China uses a single time zone.
Where does a new day begin on Earth?
Just west of the International Date Line. Kiribati moved the line in 1995 so its easternmost islands, at UTC+14, are among the first places to enter each new day.