London, part 2 - The Prime Meridian

Here is the Prime Meridian, the imaginary line that cuts the world in half vertically. The official marker for the Prime Meridian is located at London's Royal Observatory.
This is the new Prime Meridian. It was created in 2000. Pretty artsy, huh?

On the ground, there is a list of major world cities and their longitudes.

Here is the old Prime Meridian. This is what I saw in 1994, the first time I came to London. It has been demoted. It lies behind a gate and there is no sign pointing toward its existence.