Great Pyramid Astronomy

I have NASA and Astronomy listed as off topic, but in a way, they are actually a huge part of archaeology, and Egyptology. The Ancient Egyptian who was in charge of the building of the first true pyramid was Imhotep. Imhotep was an astronomer, High Priest of the sun god Ra, and chancellor to the Pharaoh Djoser (Zo-sir)(reigned c.2630 - c.2611 BC).

The pyramid Imhotep built is called the Step Pyramid and is at Saqqara. The pyramid was massive by the standards of the time; the base covered 37 acres (0.05 mi.), which was the size of a fairly large town then. The pyramid has six steps or mastaba, rising to a height of 197ft, with the base 397x358 feet sq. and it contains 11,668,000 cubic feet of clay and stone.

Underground, the pyramid goes down for 3 1/2 miles of tunnel, shafts, stairwells, galleries, vaults, and passages.

How does this relate to astronomy? Well, Djoser's grandson, Pharaoh Khufu (Cheops his Greek name), took his grandfather's tomb to the next level so to speak, and built the Great Pyramid of Giza.

The axis of the pyramid is lined up with what the Egyptians called the "hoof star," in the constellation of the Bull's Foreleg (outlined in black in the image; click for larger view). We call the star Benetnasch or Alkaid, and it is part of Ursa Major--the Great Bear constellation.

The Great Pyramid is the most accurately aligned of all the Egyptian pyramids; the average deviation from True North is a little more than 3 minutes of a degree. That means that the foundation is level to within less than an inch of True North.

In 2000, Kate Spade, a scientist at Cambridge University--pointed out something interesting. When the Great Pyramid was built, it's accuracy was perfect and now it has shifted. She thinks it is because the Earth's axis tilt rotates somewhat like a gyroscope, so the celestial North Pole seems to move. The rate of movement is so slow it is imperceptible to the naked eye since the cycle takes nearly twenty-six thousand years to complete.

However, when the pyramid was built, no one star was aligned to True North. The stars that could potentially have been used weren't in the correct place until seventy years after the pyramid was built, so the debut continues as to which stars were used.


Information from Building the Great Pyramid by Kevin Jackson and Jonathan Stamp pub. 2003 by Firefly Books Ltd.

Image of the Denderah Zodiac is from here. The bold line was added by me for clarity.