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Royal Observatory
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Stand on the historic Prime Meridian of the World at Royal Observatory Greenwich, the home of Greenwich Mean Time (GMT).

Since the late 19th century, the Prime Meridian at Greenwich has divided the eastern and western hemispheres of the Earth - just as the equator divides the northern and southern hemispheres.

In 1884 the Prime Meridian was defined using the Transit Circle telescope at the Royal Observatory. The cross-hairs in the eyepiece of the telescope precisely marked Longitude 0° for the world.

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What is the Prime Meridian?

A meridian is a north-south line, selected as the reference line for astronomical observations. By comparing thousands of observations taken from the same meridian, it's possible to build up an accurate map of the sky.

Any north-south line can be referred to as a meridian. The 'Prime' meridian however is the line defined as Longitude 0°: the spot from which all longitudes and time zones east and west can be measured.


Why is the Prime Meridian in Greenwich?

There were two main reasons for the choice. The first was the fact that the USA had already chosen Greenwich as the basis for its own national time zone system.

The second was that in the late 19th century, 72% of the world's commerce depended on sea-charts which used Greenwich as the Prime Meridian.

By naming Greenwich as Longitude 0º, it would be advantageous to the largest number of people. Therefore the Prime Meridian at Greenwich became the centre of world time.

Learn more at the Royal Observatory

Visit the home of Greenwich Mean Time (GMT), the Prime Meridian of the world and London’s Planetarium.

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Royal Observatory

  • Walk the Prime Meridian line
  • See the best view in London
  • Guaranteed entry time
  • Audio guide included
  • Planetarium shows not included
Adult £20
Child £10

Royal Museums Greenwich Day Pass

  • Save 25% with combo ticket
  • Cutty Sark
  • Royal Observatory
  • Guaranteed entry time
  • Planetarium shows not included
Adult £30
Child £15

Member tickets

  • Unlimited free entry
  • Priority booking and exclusive events
  • Access using your membership card
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  • Royal Observatory
  • Cutty Sark
  • Planetarium Shows
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