1-152-344 - Ann Ronan Picture Library/Heritage-Images

Great Pyramid of Cheops at Giza being used as an astronomical observatory. Illustration demonstrating Piazzi Smyth's theory that a passage from the lower of the two subterranean chambers (A) was used to observe the Pole Star at its lowest culmination, while the passage from the higher chamber was used to observe the Pole Star at its upper culmination. British astronomer Charles Piazzi Smyth (1819-1900) travelled to Egypt in the 1860s to undertake measurements of the Great Pyramid. He believed that the dimensions of the pyramid had mystical significance, a theory that failed to gain widespread acceptance.