I had an interesting visit this weekend to the Royal Observatory at Greenwich in London - the place where East meets West!
Until quite recently (150 years ago!) every town in the world kept its own local time. There was no formal way which set how time should be measured, or when the day would begin and end, or what length an hour might be.
With the expansion of railway and communications networks in the mid-1800s, there needed to be an international time standard for all these towns across the world so Greenwich was chosen as the centre for world time. Since 1884, the Prime Meridian at Greenwich in London, UK, has served as the reference line for Greenwich Mean Time (GMT). But why London? The USA had already chosen Greenwich as its national time zone system and also in the late 19th century, over 70% of the world’s commerce depended on sea-charts which used Greenwich as the Prime Meridian.
Just over 100 years later a new set of coordinate systems were adopted based on satellite data and other measurements. The true prime meridian of the world, as agreed by every nation on the planet in 1984, is the IERS Reference Meridian, which is also known as the International Reference Meridian or IRM that passes 102.5 metres to the east of the historic Prime Meridian. The entire Observatory and the historic Prime Meridian now lie to the west of the true prime meridian… this is why the reference on the Google map only gave a reading of 0° 0° 2° when I walked the original line!