Greenwich Mean Time facts for kids

Time zones of Europe in relation to UTC:

blue	Western European Time (UTC+0) Western European Summer Time (UTC+1)
light blue	Western European Time (UTC+0)
red	Central European Time (UTC+1) Central European Summer Time (UTC+2)
yellow	Eastern European Time (UTC+2) Eastern European Summer Time (UTC+3)
orange	Kaliningrad Time (UTC+3)
green	Further-eastern European Time (UTC+3), a.k.a. Moscow Time

Light colours indicate countries that do not observe summer time.

Greenwich Mean Time (often called GMT) is a special way of telling time that is used all over the world. It's like a main clock for many countries, including the United Kingdom and Portugal.

GMT helps everyone know what time it is in different places. It's very similar to another time system called UTC. While they are almost the same, UTC is a bit more modern and precise, especially for science.

What is Greenwich Mean Time?

Greenwich Mean Time is based on the Prime Meridian, an imaginary line that goes from the North Pole to the South Pole and passes through Greenwich, a part of London, England.

The Prime Meridian

The Prime Meridian is like the starting point for all time zones around the world. It's marked by a special telescope at the Royal Observatory, Greenwich. When it's 12:00 PM (noon) at the Prime Meridian, that's the official GMT.

How Time Zones Work

The Earth is divided into 24 main time zones, like slices of an orange. Each slice represents one hour. As you travel east from the Prime Meridian, you add an hour for each time zone. If you travel west, you subtract an hour.

GMT and UTC: What's the Difference?

GMT and UTC are very closely related. For everyday use, people often use them to mean the same thing. However, there's a small difference:

• GMT is based on the Earth's rotation and the position of the sun. It's an older way of keeping time.
• UTC is a more modern and exact time standard. It uses very precise atomic clocks to keep time. Scientists and computers often use UTC because it's super accurate.

So, while GMT is still widely used, UTC is the official international time standard that helps keep everything perfectly in sync.

Where is GMT Used?

GMT is the official time zone for several countries, especially those close to the Prime Meridian. These include:

• United Kingdom
• Portugal
• Ireland
• Iceland
• Many countries in West Africa, like Ghana

When these countries are not using Daylight Saving Time, their clocks are set to GMT.

Images for kids

• 

  Greenwich clock with standard measurements

• 

  Clock in Kumasi, Ghana, set to GMT.