Imagine shining a flashlight at a globe. Only part of the globe would receive light, while the opposite side of the globe would be dark. As Earth rotates, different parts of Earth receive sunlight or darkness, giving us day and night.
If we had one single time zone for Earth, noon would be the middle of the day in some places, but it would be morning, evening, and the middle of the night in others. Since different parts of Earth enter and exit daylight at different times, we need different time zones.
Distance between the zones is greatest at the equator and shrinks to zero at the poles, due to the curvature of Earth. Since the equator is approximately 24,902 miles long, the distance between time zones at the equator is approximately 1,038 miles.
The imaginary dividing lines begin at Greenwich, a suburb of London. The primary dividing line of longitude is called the prime meridian. Longitude is the angular distance between a point on any meridian and the prime meridian at Greenwich.
The time at Greenwich is called Greenwich Mean Time (GMT). As you move west from Greenwich, every 15-degree section or time zone is an hour earlier than GMT, while each time zone to the east is an hour later.
Having different time zones means that no matter where you live on the planet, your noon is the middle of the day when the sun is highest, while midnight is the middle of the night. Let's take a closer look at how this works.
Let's say you live in Charlotte, North Carolina, and you have a cousin who lives in Madrid, Spain. Charlotte is five time zones to the west of Greenwich, which is written as GMT -5. Madrid is 1 section east of Greenwich (GMT +1). This means Charlotte and Madrid are six time zones apart.
When your cousin is eating lunch at noon Madrid time, you are probably just getting out of bed to get ready for school. This is because at 12:00 p.m. in Madrid, it's only 6:00 a.m. in Charlotte. On the other hand, if you wanted to chat with your cousin online after dinner at 6:00 p.m., it would already be midnight in Madrid!