Setting Out: Building Pyramids
Many claims are made for the 'unusual accuracy' of the construction ofthe great pyramid.
Many of those who make the claims seem to ignore simple maths and surveying techniques.
Flat leather measuring tape is fairly inelastic, and can be used to draw a circle with a radius of the corners of the pyramid. You can measure distances extremely accurately with a long pole with a sharp pin fixed at right angles at each end, to confirm the important corners of the pyramid.
The obvious way to find true North South is to use the shadow of the sunfrom a tall pole. I tried this and it doesn't work. The tip of the shadow is too fuzzy because the sun is not a point, and you get slightly different shadows from each side of the sun.
The trick is to use a star at night. Select a star low enough in the sky so that its shadow( if it cast one) crosses your circle that encloses the base a couple of hours each side of its highest point. Now a star wont cast a shadow, but if you place a mirror (shallow bowl of mercury or water) flat on the ground, you can easily sight the star against the sharp top point ofthe center pole, and mark the ground as its shadow moves.
You should be able to mark the point of the shadow to an accuracy of 1mm. These marks will trace a parabola on the ground that will cut the outercircle.
Draw a straight line that joins these two points. This line runs true eastwest.
From each of these two points use the long measuring rod to draw two more circles that overlap. These new circles cross each other exactly on the north south line, accurate to within a few milimetres.
Once you have marked out the corners of the pyramid, you can confirm that these are exact by sighting another, lower star that gives a parabola that crosses the exact point of the corner on the circle. The NW and NE corners should be exact. Any discrepancy is probably due to movement from earthquakes.
This information is copyright Peter Thomson 2001-2004