The Great Pyramid

R. A. Proctor

[Extracted from Knowledge, vol. 1, 10/3/1882, p. 400.]

WE have seen that the Great Pyramid is so perfectly oriented as to show that astronomical observations of great accuracy were made by its architects. No astronomer can doubt this, for the simple reason that every astronomer knows the exceeding difficulty of the task which the architects solved so satisfactorily, and that nothing short of the most careful observation would have enabled the builders to secure anything like the accuracy which, as a matter of fact, they did secure. Many, not acquainted with the nature of the problem, imagine that all the builders had to do was to use some of those methods of taking shadows, as, for instance, at solar noon (which has to be first determined, be it noticed), or before and after noon, noting when shadows are equal (which is not an exact method, and requires considerable care even to give what it can give—imperfect orientation), and so forth. But to give the accuracy which the builders obtained, not only in the orientation, but in getting the Pyramid very close to latitude 30° (which was evidently what they wanted), only very exact observations would serve. Indeed, if a modern astronomer, knowing nothing about the Pyramid, were asked how the thing could be done without telescopic aid, he would be apt to say that no greater accuracy than (for instance) Tycho Brahe obtained with his great quadrant at Uranienburg could have been secured. Now, the orientation of the Great Pyramid approaches much closer to exactness than the best observations by Tycho Brahe with that justly celebrated instrument.

The Pyramid Observatory, showing the object-end of the great observing tube.


Seeing this, and observing that the ascending and descending passages are just such as the astronomer would make to secure such a result, we may accept, without a particle of doubt, the belief that they were made for that purpose.

Then we saw that the features of the Great Ascending Gallery were not such as would be essential, or even desirable, to increase or maintain the accuracy of the orientation, as layer after layer was added to the Pyramid, but are precisely such as would be essential if the Pyramid was meant to subserve (as one, at least, of its objects) the purpose of an observatory.

But persons unfamiliar with astronomy will say (several have said so in letters addressed to me). This great ascending gallery would only enable astronomers to observe stars when due south, or nearly so, and only those which, when due south, were within a certain distance above or below the point towards which the axis of the Great Gallery is directed. Were all the other stars left unobserved? And again, we know that the Egyptians, like all ancient astronomers, paid great attention to the rising and setting of the heavenly bodies, and especially to what was called the heliacal rising and setting of the stars. In what way would the Great Gallery help them here?

Now, with regard to the first point, we note that the chief instrument of exact observation in modern observatories, the one which, as it were, governs all the others, has precisely this quality—it is always directed to the meridian, and has, indeed, a very much narrower range of view on either side of the meridian than the Great Gallery had. And though it is indeed free to range over the whole are of the meridian from the south horizon point through the point overhead to the north horizon point, it is mainly employed over about that range north and south of the celestial equator which was commanded by the Great Gallery. The visitor at Greenwich sees the great equatorial, and imagines that to be the chief observing instrument. The comparatively unobtrusive transit circle seems far less important. But the time observations, which are far and away the most important observations made at Greenwich, are all made, or at least, all regulated, by the transit observations. So are the observations for determining the positions of stars.

When the equatorial is used to make a time or position observation, it is used as a differential instrument, it is employed to determine how far east or west a star may be (theoretically, how much it differs in right ascension measured by time) from another; and again, to show how far north or south a star may be (theoretically how much it differs in declination) from another, whose right ascension and declination have already been determined by repeated observations with the transit circle. Similarly, the altitude and azimuth instrument is used in direct subordination to the transit circle.

Vertical Section of the Pyramid Observatory through the plane of the passages and gallery,
 showing the range of view of the great observing tube.

The astronomers who observed from the Great Pyramid doubtless made many more observations off the meridian than on it. They made multitudinous observations of the rising and setting of stars, and especially of their heliacal risings and settings (which last, however, though we hear so much of them, belonged ex necessitate to but a very rough class of observations). They no doubt often used astrolabes and similar instruments to determine the positions of stars, planets, comets, &c., when off the meridian, with reference to stars whose places were already determined by the use of their great meridional instrument. But all those observations were regulated by, and derived their value from, the work done in the Great Ascending Gallery. The modern astronomer sees that this was the only way in which exact observations of the heavenly bodies all over the star-sphere could possibly have been made; and seeing the extreme care, the most marvellous pains, which the astronomers of the Great Pyramid took to [p.400] secure good meridional work, the astronomer recognises in him a fellow-worker. He says, with the poet:—

I am as old as Egypt to myself,
Brother to them that squared the Pyramids:
By the same stars I watch.

And now consider what was this great observatory of ancient Egypt—the most perfect ever made till telescopic art revealed a way of exact observation without those massive structures. A mighty mass, having a base larger than the square of Lincoln's Inn, rising by just fifty layers to a height of about 112 feet, and presenting towards the south the appearance shown in Fig. 1, where the mouth of the Great Gallery is seen opening southwards, and the lines are shown which have been already indicated as "observing directions" in the picture on p. 315. The Pyramid observatory is shown in section in Fig. 2. It will be noticed that the successive layers are not of equal thickness. There arc just fifty between the base and plane of the floor of the Kings Chamber. The direction lines for the mid-day sun at midsummer, midwinter, and the equinoxes are shown; also the lines to the two stars, Alpha Draconis and Alpha Centauri, are given at the subpolar meridional passage of the former and the meridional passage of the latter, at the date when the descending and ascending passages thus commanded both these stars. Within fifty years or so on either side of this date, the Pyramid must, I should think, have been built. The later date when Alpha Draconis was at the right distance from the Pole, 2170 B.C.,* is absolutely rejected by Egyptologists—not one being ready to admit that the date of the Pyramid King can have been anywhere near so late.

* Some may be disposed to reject a change which they may imagine displaces the Pleiades from the position which Professor Piazzi Smyth assigned to that interesting group at the date when he supposed the Pyramid was built. But there never was the least real significance in that position. If the mistaken idea entertained by many, and repeated by Flammarion, Haliburton, and others, that the Pleiades at their meridian shone down the Great Gallery at the very time when the Pole Star of 2170 B.C. shone down the descending Gallery, had been correct, there might have been some reason to be struck by the coincidence. But it should hardly be necessary to tell the reader what every astronomer knows, that the Pleiades never did or could shine down the Great Gallery, and in the year 2170 B.C. were thirty-eight degrees (!) north of that position.