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Astronomy and the Great Pyramid

J. Donald Fernie

Pointing at the Heavens

The first modern European astronomer on the scene was probably John Greaves, a professor of geometry at Gresham College. In 1637, Greaves suddenly abandoned the academy in order to undertake measurements of the Great Pyramid. His work was thorough and extensive, and Newton and others scrutinized the published results for data to develop their theories. Upon his return to England in 1640, Greaves's reputation won him the Savilian Professorship of Astronomy at Oxford. Unfortunately, he fell from this lofty position after being fired for misappropriation of funds!

Some two centuries later, a much more famous astronomer named Charles Piazzi Smyth, Astronomer Royal for Scotland, turned his attention to the Pyramid. A curious figure, Smyth produced some first–rate science in other fields, but he lost almost all rationality when it came to this subject. For example, he attributed great significance to the fact that the slope of the Pyramid is near the ratio 10:9, and that its height of 484.9 feet (or 0.09184 mile) multiplied by 109 equaled 91,840,000 miles. Coincidentally, that number is close to the actual distance between the Earth and the Sun. Smyth believed that the coincidence meant that the Pyramid builders must have also known this distance. There was much more along these lines, with liberal doses of religious and prophetic conclusions. He published a three–volume, 1,600–page opus about his findings, which, needless to say, was a great hit among the like–minded, but which was dismissed by one reviewer as containing "more extraordinary hallucinations than has appeared in any other three volumes of the past century." Nevertheless, Smyth was not entirely without redemption. Like a previous investigator, he was intrigued by the extraordinary straightness of the Descending Passage and took care to measure carefully its angle of descent, noting that a person within the passage looking out through the surface opening would see a patch of sky close to the celestial north pole. However, Polaris, the current pole star, would not have been visible to the builders because precession (the slow wobble of the earth's axis of spin) would have placed the pole much farther from Polaris than it is now. A possible (though not very likely) pole star for people of that era is the magnitude 3.7 star Thuban (Alpha Draconis), which, Smyth calculated, would have been visible in the opening at lower culmination (the time of its lowest point in the sky) around the years 2123 and 3440 B.C. He suggested that the Pyramid might have been built near either of those dates, which despite the flimsiness of his argument is not entirely ridiculous when compared to the modern estimate at about 2500 B.C.

Figure 2. The apparent movements of the stars...Click to Enlarge Image

A long–standing problem relating not only to the Great Pyramid but also its smaller cousins is the question of how the builders managed to orient such colossal structures to the cardinal points with surprisingly high accuracy. The eastern side of the Great Pyramid, for example, points only three arcminutes away from a true north–south line, and other pyramids in the group are not much worse. This makes it virtually certain that some astronomical method was used to establish the local meridian. At first thought this does not seem too difficult a problem, even without a bright star close to the north celestial pole during the millennia of interest. (Even today, Polaris is some 43 arcminutes from the pole, and during this time it was about 25 degrees away.)

Still, other possibilities spring to mind. An obvious method would be to note the directions of sunrise and sunset on a given day and bisect the angle between the two—the result marks the meridian. But this, and other seemingly straightforward methods, while fine in principle, turn out to be unsatisfactory in practice, at least when accuracies of a small fraction of a degree are called for. For instance, in this case the rising and setting sun must be seen over an absolutely flat horizon, which Giza lacks. Then there is refraction in the earth's atmosphere: When one sees the lower edge of the setting sun just touching the horizon it has in fact already set. The light rays are bent to produce an image above the horizon, thereby shifting the direction in which the sun appears to set. And since the amount of refraction depends on air temperature, pressure and other factors, all of which can differ between morning and evening, the effect may not be consistent between rising and setting. Furthermore, the sun's celestial coordinates will change during the course of the day, spoiling the symmetry of the method. All in all, these practical hurdles have stymied modern astronomers who tried to figure out just how the early Egyptians managed to orient their pyramids as precisely as they did.

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