1-152-291 - Ann Ronan Picture Library/Heritage-Images

Great Pyramid of Cheops at Giza being used as an astronomical observatory, 1891. Artist's reconstruction illustrating Piazzi Smyth's theory, showing ancient Egyptian priests making astronomical observations from a chamber within the Great Pyramid. 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.