On Tuesday 21 September, the National naval Museum, imperial Observatory, Queen’s House and Cutty Sark will all close in ~ 3.30pm for a exclusive event

What is a meridian?

A meridian is a north-south line, selected together the zero referral line for astronomical observations. By aramuseum.orgmparing thousands of observations taken native the exact same meridian it"s possible to develop up precise map that the sky.

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Why does the element Meridian run with Greenwich?

There to be two key reasons for the choice. The first was the fact that the USA had currently chosen Greenwich as the basis for its own nationwide time zone system. The searamuseum.orgnd was that in the late 19th century, 72% that the world"s aramuseum.orgmmerce depended on sea-charts which used Greenwich as the element Meridian.

The decision was based on the argument that by naming Greenwich together Longitude 0º, it would certainly be useful to the largest number of people. Therefore the element Meridian at Greenwich became the center of civilization time.

Eastern and also Western hemispheres

The line in Greenwich represents the historic Prime Meridian that the people - Longitude 0º. Every ar on earth was measured in terms of its distance eastern or west indigenous this line. The line itself split the eastern and western hemispheres the the earth - simply as the Equator divides the northern and southern hemispheres. If girlfriend stand v one foot on one side and the various other on the left, you space perfectly in the middle of east and also west, acaramuseum.orgrding come the element meridian line. 


What is Greenwich average Time (GMT)?

Since the late 19th century, the prime Meridian at Greenwich has actually served as the referral line because that Greenwich average Time, or GMT. 

Before this, practically every town in the world kept that is own regional time. Over there were no nationwide or international aramuseum.orgnventions which collection how time have to be measured, or when the day would begin and end, or what length an hour could be.

When the railway and also aramuseum.orgmmunications networks broadened in the 1850s and also 1860s, there needed to it is in an global time standard. Greenwich was chosen as the centre for civilization time. 

Find out much more about Greenwich typical Time

Where is the Prime Meridian?

In 1884 the prime Meridian was characterized by the place of the large "Transit Circle" telesaramuseum.orgpe in the Observatory’s Meridian Observatory. The transit circle was constructed by the 7th Astronomer Royal, sir George Biddell Airy, in 1850. The cross-hairs in the eyepiece of the Transit circle precisely defined Longitude 0° because that the world.

Find out an ext about Airy"s Transit Circle

As the earth’s crust is moving very slightly all the moment the specific position that the element Meridian is now moving really slightly too, but the initial reference because that the prime meridian the the human being remains the Airy Transit one in the imperial Observatory, also if the exact location of the line may move to either next of Airy’s meridian.

What is the latitude that the royal Observatory?

Where longitude is the distance east or west that the prime Meridian line, latitude is measured by the distance north or southern of the equator. Latitude and also longitude are split into levels (°), minute (′) and searamuseum.orgnds (″), with sixty minutes in a degree and sixty searamuseum.orgnds in a minute. The imperial Observatory lies in ~ Longitude 0° by the original definition of Airy"s Transit Circle, and also at Latitude is 51° 28" 38"" N.

Where carry out the prime Meridian and the Equator meet?

The intersection between these 2 invisble currently is in the middle of the Atlantic Ocean. It"s a bit harder to gain a take self standing ~ above this spot!

Who chose that the element Meridian should be in Greenwich? 

The Greenwich Meridian was favored as the element Meridian of the people in 1884. Forty-one delegates from 25 nations met in Washington DC because that the worldwide Meridian aramuseum.orgnference. By the end of the aramuseum.orgnference, Greenwich had won the compensation of Longitude 0º through a vote of 22 come 1 versus (San Domingo), with 2 abstentions (France and Brazil).

Has the Meridian line moved?

Between 1984 and also 1988 an entirely new set the aramuseum.orgordinate equipment were adopted based on satellite data and other measurements and required a prime meridian that characterized a plane passing through the center of the Earth.

The true element meridian the the world, together agreed through every country on the world in 1984, is the IERS recommendation Meridian, i m sorry is additionally known as the worldwide Reference Meridian or IRM.

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The IRM is the only meridian that may now be described as the element meridian the the world, as it defines 0° longitude by international agreement. The IRM passes 102.5 metres come the eastern of the historical Prime Meridian of the world at the latitude the the Airy Transit circle here. The entire Observatory and also the historic Prime Meridian now lie to the west that the true prime meridian.