ironychan:

It’s not uncommon knowledge that the sides of the Egyptian pyramids are aligned with the compass points: North, South, East, and West, which is mildly impressive since ancient Egyptians didn’t have compasses.

It’s a little more impressive when you stop to think about the fact that there was no north star back then, because over time earth’s axis wobbles with respect to the stars. We’re just lucky to live at a time when there’s a star in about the right spot.

It becomes incredibly impressive when you read the article in a 2000 issue of Nature, in which Egyptologist Kate Spence plots the errors in this alignment and shows that they drift on a predictable pattern. That pattern is the aforementioned polar wobble. This tells us two things:

1) Despite the lack of a stationary north star, the Egyptians used the stars to lay out the bases of their pyramids. They did this so carefully that we can see evidence of a 26,000-year cycle in the orientations of monuments built over a period of a few hundred years. Holy shit.

2) The start dates for the construction of each pyramid. The great pyramid of Khufu was begun in 2478 BC, plus or minus five years. Probably in October, which would have been the best time of year to make the measurement. HOLY FUCKING SHIT.