Ancient Skies

NARRATOR

But how did builders achieve such an astonishing level of accuracy, over 4,500 years ago? It's easy to think that ancient people didn't really know how to do any of this stuff, but in fact, they understood the way the sun moved, they understood the way the shadows moved. They had the knowledge of astronomy and geometry and engineering that was fine for doing this sort of thing. They were able to find the directions of north, south, east and west pretty accurately. And all you need......is a long stick......a plumb bob... and a hammer. This long stick is called a gnomon, and if you stick it in the ground straight up and down, it will cast a shadow due to the sunlight. Yeah, that's not bad. Now that we have our gnomon in the ground and it's straight up and down, it's casting a shadow due to sunlight. Now all we have to do is mark the end of that shadow several times over the course of the day. That's going to make an arc on the ground as the sun rises and sets. And that's what's going to help me find east and west. Once we have the arc in the ground representing the length of the shadow over the course of the day, we could take a piece of string and tie it to this gnomon, move out a certain distance, and then just use that to draw a circle in the ground. That circle will intersect the arc in two spots. Draw a line connecting those two points... That points east and west.

NARRATOR

Experts believe this is how the ancient Egyptians used the sun to align the pyramids of Giza to north, south, east and west.