Ticketed Essential Information Location Royal Observatory Price Included with entry to the Observatory Free entry for members . Not a member? Join now Book tickets Plan your visit to the Royal Observatory Stand on the historic Prime Meridian of the World at Royal Observatory Greenwich, the home of Greenwich Mean Time (GMT). Grab an iconic selfie and share using #PrimeMeridian Discover the remarkable story of the place that gave Greenwich Mean Time (GMT) to the world Explore the highlights of the historic Royal Observatory, from the Great Equatorial Telescope to the beautiful Octagon Room Look out across London from the Meridian Courtyard, and see how many city sights you can spot from Greenwich! 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. Visit the Royal Observatory Image 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. Image 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. Find out more Learn more at the Royal Observatory Visit the home of Greenwich Mean Time (GMT), the Prime Meridian of the world and London’s Planetarium. Find out more Book tickets Top things to do From historic clocks and telescopes to cutting edge astronomy, find all there is to see at the home of Greenwich Mean Time Plan your visit Plan your visit to the Royal Observatory Families at the Royal Observatory Bring your little astronauts to the Royal Observatory for space-themed fun Shop Greenwich Shepherd Gate 45cm Wall Clock, 24-Hour Analogue Dial £150.00 Own a Shepherd Gate 45cm clock, exclusively available from the home of Greenwich Mean Time. A stylish 24-hour analogue clock that will make a statement on any wall, with its bold monochrome face, and matte black metal casing... Buy Now Shop About Time Too: A Miscellany of Time by Royal Observatory Greenwich £12.99 How old is Earth? How fast can you think? How long is a light year and how short is a femtosecond? What does Greenwich Mean Time mean? Can you tell the time with flowers? When did time begin? This light-hearted, illustrated miscellany from Royal Observatory Greenwich goes a long way to answering some of these questions and also presents a whole range of other amazing facts and figures which show the influence of time on our daily lives... Buy Now Shop On the Line: The Story of the Greenwich Meridian £8.99 The Royal Observatory at Greenwich is the home of time and space, the Prime Meridian and Greenwich Mean Time (GMT). But have you ever stopped to ask what is the Prime Meridian and why it is at Greenwich? Why are all time zones across the world based on GMT? What is longitude and why is the meridian moving? Written by Dr Louise Devoy, Senior Curator of the Royal Observatory at Royal Museums Greenwich... Buy Now Royal Museums Greenwich Close Choose your tickets Royal Observatory Walk the Prime Meridian line See the best view in London Guaranteed entry time Audio guide included Planetarium shows not included Adult £18 Child £9 BOOK NOW Royal Museums Greenwich Day Pass Save 25% with combo ticket Cutty Sark Royal Observatory Guaranteed entry time Planetarium shows not included Adult £27 Child £13.50 BOOK NOW Member tickets Free and fast-track Museums entry Priority booking Access using your membership card Membership card number required BOOK NOW Become a Member Unlimited entry all year Royal Observatory Cutty Sark Planetarium Shows Special exhibitions Direct Debit One-off Individual: £50 Individual: £60 Family: from £60 Family: from £70 JOIN TODAY