If you have ever looked at a globe, you have seen the vertical lines running from the North Pole to the South Pole. The most important of these is the —specifically, the Prime Meridian .
A meridian is a . Unlike lines of latitude (which run parallel like steps on a ladder), meridians are not parallel. They all converge at the North and South Poles. Every point on Earth lies on a specific meridian, defining its east-west position. meridian line
You don’t just have to imagine it. At the Royal Observatory in Greenwich, you can stand with one foot in the Eastern Hemisphere and one foot in the Western Hemisphere. A physical brass line (and a powerful green laser at night) marks the for tourists. If you have ever looked at a globe,