So, I mentioned that the prime meridian which runs through Greenwich England. So, it goes from the North Pole right through the plane of the earth actually. But you can think of it as a line across the surface down to the South Pole. So, it goes through this beautiful town in England just outside of London called Greenwich. So, why Greenwich? Well, it was chosen in 1884. It's interesting because before that time, there were lots of different prime meridians that were being used. Different countries had adopted their own prime meridian. So that, for example, France had their own prime meridian because they wanted to use a system that related to their country and they all we're in a way, I think, competing for who was going to become the standard. So, the United Kingdom had their own prime meridian. I think some other countries did as well. As sea navigation became more common and became faster, people decided that well we have to standardize on a system of navigation and maps. So, they were all working off the same framework. So, they said, okay, we have to get together, we've to come up with one prime meridian that we can all agree on and then we'll just use that. So, that's what they did. They got together. There was 41 delegates from 25 countries. They met in Washington DC for the International Meridian Conference. I'll bet that was a heck of a party. Just saying. So, the US had already chosen Greenwich as the basis for their time zone system, and 72% of the world's commerce at the time depended on see charts, which had already adopted Greenwich as the prime meridian. So, in other words, it was the fact old standard already, and it seemed a no-brain for them to say well, most people are using this one anyway. So, let's all just adopt the British standard and go with Greenwich, and so that's what they did. So, that's why it's in Greenwich. But where in Greenwich? Where is this line? So, they just said, okay we're going to have the prime meridian go through Greenwich. But where in Greenwich? I'm the type of person that wants to know these things. Well, it goes through the Royal Observatory in Greenwich. Okay. That's good. But where in the Royal Observatory? Well, it actually goes through the Airy Transit, okay, which is a special telescope. It doesn't just go through Airy Transit. Where in the Transit? It's basically this telescope. Well, the thing that I find amazing, I don't know, I just love this little bit of trivia, is that it actually, the prime meridian for the entire world goes through the eyepiece of this telescope, basically. But where in the eyepiece? Are you getting tired of this yet? There's actually a spiderweb cross hair through the eyepiece of the telescope in the Royal Observatory in Greenwich England and where are those two spider webs cross is the definition of the prime meridian for the entire world. Pretty cool. At least it was the definition at that time. It's shifted. It gets into more complex ways of describing things that we'll mention a bit later. But at this time, that was how they defined all of the navigation and all the longitude and latitude coordinates for everyone to use everywhere in the world, was based on the cross hairs in the eyepiece of this telescope. Pretty awesome. So, why was it called the Airy Transit? It was developed by Sir George Airy in 1850. So, you can see him here. He's admiring, looking at his Transit that he built. He actually designed and built this thing himself for observing the stars and watching how the stars move across the sky. I won't go into the details of this. But a different kind of telescope than you might normally see is that the telescope doesn't actually move around to look at different parts of the sky. It just opens up and looks at one section of the sky and looks at the stars and the planets as they move across it, as they make a transit across the sky from one part of the telescope to the other. So, that's where I gets the name the Transit. So, this is the rather unassuming building that it's in. So, these photos I took while I was there, I was visiting Greenwich a few years ago. I took a couple of photos for me. This was like a big moment to actually see the the prime meridian. If you notice, you can just see here that this is actually the line, that's the prime meridian. So, they have this metal line that goes out on to the pavement. The top of this actually opens up this building just like a hatch that opens up, and that's how the Transit is able to see the sky. So, great place to visit if you ever have a chance at least if you're a geo nerd like me.
