See the map Since countries are free to ... are time zones across the United States, there are time zones around the world to reflect the Earth's rotation around the sun. Those world zones even ...

This means: Time zones are not always in straight lines on the longitudes on Earth. This is because they may need to curve around country borders. You can see this in the map below. It is night ...

The sun is shining on her side of the Earth ... night-time. Because the time is different depending on where you are in the world, everyone has agreed to split the world up into time zones.