The Prime Meridian is 125 years old this week. That's the imaginary north-south line through Greenwich which divides the world into western and eastern hemispheres, and from which longitude and universal time are measured. It passes less than a kilometre from my house. And we'd be lost without it.
Noon was once simply the time when the sun was directly overhead. The advent of rail travel in the 19th century forced many countries to standardise time based on a national meridian. The UK adopted Greenwich Mean Time in 1880, while the French preferred their own meridien through Paris instead. A global standard was required, so in 1884 US President Chester Arthur invited delegates from around the world to Washington to attend the first (and last) InternationalMeridianConference.
There are an infinite number of possible meridians, each stretching from the North to the South Pole, and any one of these could have been chosen. However, the Greenwich Meridian was pre-eminent because it had already been adopted by both the UK and USA and was therefore being used by 72% of the world's shipping. The French eventually backed down, but only in return for the rest of the world agreeing to think about adopting their system of metric measures. The crucial conference vote was taken on 13 October 1884, with France and Brazil abstaining and only San Domingo in opposition. And so time began at Greenwich (latitude 51°28'38"N, longitude 0°).
To celebrate tomorrow's anniversary I'm taking you on a week-long journey down the zero degree line of longitude, south from Greenwich, stopping off at all the places where the meridian has been marked in some way. There are plaques and monuments, bollards and arches, plus an awful lot of random everyday objects that just happen to lie on this most special of lines. I did exactly the same thing five years ago, but travelled north from Greenwich instead [words][photos]. There aren't quite so many official markers on the trek south towards the edge of London, but there's a lot more than zero.