Great sailing across the Prime Meridian under fair northerly winds and good weather.
It is 1761. Harrison has solved the problem of accurately keeping track of time at sea. His watches have been proven seaworthy and tested on long sea voyages.
Accurate positioning using latitude and longitude measurements wasn’t feasible at sea until then, when it became possible to determine the exact time when a celestial body’s projection hits the Earth’s surface, after measurements taken by instruments such as the sextant.
To calculate the longitude, it was then possible to specify the time difference between a determined location and a Coordinated Universal Time (UTC), which represents the world’s standard to regulate clocks.
The accurate timing problem solved, it still wasn’t all clear. Navigators, chart and map makers used different meridians as the starting position for time and longitude measurements. Along with the political situation throughout history, several of them have been taken as this main reference, such as the lines passing through the Canary Islands, Paris, Antwerp, London, or Berlin, amongst others.
To choose a world reference was becoming necessary. And it was in 1851 when the British mathematician and astronomer Sir George Airy proposed as Prime Meridian the one that passed by the Greenwich Royal Observatory. It was not accepted straight away, but just about 33 years later, when the International Meridian Conference was held to choose a "meridian to be employed as a common zero of longitude and standard time reckoning throughout the world."
This afternoon, with squares up to royals, lower staysails, all the headrig, and spanker, Europa sailed across this Greenwich Meridian, easting her way towards Namibia. Western Hemisphere now lays behind, in front the Eastern one. And by midnight, 1000 nm to sail to Walvis Bay.
