Liberation Day Holiday: visit to Greenwich meridian

It's almost time until the 25th April weekend and Visceglia offers you an original journey to discover London, making a stop at the Royal Observatory in Greenwich.

Greenwich is a neighborhood in south London, where the meridian of the same name passes. Also called zero meridian, since it is equal to zero longitude, it is an imaginary circumferential arc that divides planet Earth into two hemispheres and is considered an important international standard, a geographical and temporal reference point for the various countries of the world. In fact, through the meridian, the Earth's surface is ideally divided into 24 segments or spindles: each segment corresponds to a different hour of the 24 hours taken by the Earth to complete an entire rotation around its axis.

The idea of ​​a meridian that divided the Earth in two exploded again in 1675, when King Charles II of England commissioned the astronomer royal Sir Christopher Wren and his assistant Sir Robert Hooke to solve the problem of longitude in navigation. Until then, the Iron Island Meridian, developed by Ptolemy and corresponding to the Canary Islands, 20° west of Paris, was in force. The Iron Island meridian lost credibility when it was realized that it did not pass exactly 20° west of Paris, but rather at 20° 29′ 5″.

The question was resolved in the second half of the nineteenth century: on 13 October 1884, in Washington, 41 delegates from 25 countries, in the presence of the President of the United States of America, identified the imaginary circumference passing through Greenwich as the zero meridian. This meridian was useful for orienting oneself with nautical charts and obtaining a universal reference time.

The decision to make the zero meridian coincide with Greenwich depended on the presence of the Royal Observatory on the site, an observatory with a long tradition in the analysis and development of solutions in the cartographic and nautical fields. Today, interesting exhibitions for astronomy and cartography enthusiasts are held at the Royal Observatory in Greenwich, an attraction not to be missed on your visit to the city of Big Ben.

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