Sailing the River Thames to London, a memorable moment occurs when you sail past the Prime Meridian. It is marked by several plaques, monuments, and statues throughout the city. It is even marked by a powerful green laser shining north across the London night sky. But it is unlikely you will catch any of these landmarks, as you are likely to be gazing at the magnificence of the London sky line. Your GPS receiver can tell you exactly when it happens. As you can clearly see in the picture below, it showed me that I just missed the moment.
The Prime Meridian is an imaginary north-south line, which was once calculated, using the Greenwich observatory. It divides the world into western and eastern hemispheres, and from which longitude and universal time are measured. The Greenwich Meridian was most likely to be adopted by the rest of the world as most of the world's shipping was already referring to it. However, many countries’ had their own Meridian. In the year 1884 a international Meridian Conference was held in Washington DC. Attended by 41 delegates from 25 countries, it was decided that the meridian passing through Greenwich would be the official Prime Meridian.