The shafts of the Great Pyramid: do they look at the stars?

Looking through the shaft

Choose a shaft, slide through the years and watch how the proposed stars move along the axis of the shaft. The dotted ring in the viewing hole is our margin of 0.5°: a star inside it would be ‘in the shaft’. Below the viewing hole you see, for each star, how many degrees too high or too low it stands, and in the graph how that changes over the centuries.

What we know, and what is disputed

• Established in broad terms: the four shafts have angles of 45° (King’s Chamber, south), about 32.5° (King’s Chamber, north; measured at 32° 36′ 08″, the shaft bends) and about 39.5° (Queen’s Chamber, south and north; the sources give 39.1° to 39.6°). All angles come from secondary sources, and we found no measurement uncertainty anywhere.
• Only the two shafts of the King’s Chamber come out on the outside of the pyramid. The two shafts of the Queen’s Chamber are closed. The south shaft ends after about 60 m at a limestone slab with two copper pins (Gantenbrink, with a robot, 1993); the Pyramid Rover (2002) saw a second door behind it. The north shaft, which has bends, ends at a door with copper pins (Pyramid Rover). A closed shaft cannot have served as a sighting tube.
• Proposed stars: for the King’s Chamber south, the belt of Orion (Alnitak); for the King’s Chamber north, Thuban; for the Queen’s Chamber south, Sirius; and for the Queen’s Chamber north, Kochab. What exactly was proposed in 1964 and what Bauval added later is not the same in all sources (the Queen’s Chamber shafts were only measured properly in 1993). All of these assignments are disputed.
• Orion correlation: Bauval also proposed that the layout of the three great pyramids of Giza imitates the three stars of Orion’s belt. That is disputed: Edwin Krupp pointed out that the line of the pyramids bends differently from that of the belt, and Bauval disputes this. It is a different question from the one about the shafts, and we do not calculate it here.
• Whether the shafts were ever meant to be looked along is disputed. They are narrow, they have bends, and those of the Queen’s Chamber are closed; ventilation and a symbolic meaning have also been proposed. J. J. Wall wrote an article in 2007 on exactly this hypothesis (Journal for the History of Astronomy 38); we have not been able to read it yet.

Our calculation

For each star: in which year did it stand at the height of the shaft, and by how many degrees was it too high (+) or too low (−) in 2560 BC (the usual building date)? The construction window is 2560 BC ± 100 years.

The angle fixes a date poorly. If the angle is 0.5° larger or smaller, the year in which the star reaches it shifts by about 100 years (Alnitak), 90 years (Thuban), 140 years (Kochab) or 165 years (Sirius): as much as the width of the whole construction window. The margin of 0.5° is our own assumption.

What this says, and what it does not

• Orion fits best, but not exactly. Around 2560 BC Alnilam stands within 0.04° of the 45° of the King’s Chamber shaft, Alnitak 0.33° below it and Mintaka 0.44° above it: all three stars of the belt lie within our margin of 0.5°. So the angle does not pick out one star of the belt, and it does not show which one might have been meant.
• Kochab and Sirius fit roughly: Kochab stands 0.24° above the north shaft of the Queen’s Chamber, Sirius 0.50° below the south shaft, right at the edge of the margin. But those two shafts are closed.
• Thuban does not fit. Around 2560 BC it stands 1.2° below the north shaft of the King’s Chamber (with the measured 32° 36′ 08″ even 1.3°), well outside the margin. It reaches the angle only in 3243 or 2351 BC: the second time more than 200 years after 2560 BC, so outside the construction window.
• Only the two shafts of the King’s Chamber come out on the outside, so only those two could have served as a line of sight. Whether the builders intended that does not follow from angles: that remains disputed.
• Planets and the Moon are often at the height of a south shaft. Such a hit is ordinary and proves nothing, and they can never hit a north shaft (see the layer in the picture above).

How we calculate

For each star we use our model for ancient star positions (precession after Vondrák et al., proper motion from Hipparcos) to calculate where it crosses the meridian. At the latitude of the pyramid, 29° 58′ 45″ north, a star that crosses the meridian south of the zenith does so at a height of 90° minus the latitude plus the declination. For a star in the north it is 90° plus the latitude minus the declination.

We assume that the shafts lie exactly in the north–south plane and leave out refraction and nutation (together at most about 0.03°). The path of the star in the viewing hole is shown as a flat projection around the axis of the shaft.

The margin of 0.5° is our own assumption: the sources we read give no measurement uncertainty, and the shafts are narrow, bend and are partly walled up. That is why we also say how many years the result shifts if the angle is 0.5° larger or smaller.

The planets and the Moon are not calculated in the browser. We calculated the meridian transit for every day from 3500 to 1500 BC in advance with JPL’s DE441 ephemeris (via Skyfield), and checked that against JPL Horizons and against independent analytical theories. The time scale (the Earth’s rotation, ΔT) is uncertain in that period: two ΔT models already differ by about 27 minutes in 2560 BC. That is why the days in the planet layer are approximate, and not historical dates.

What we don’t know

• The angles come from secondary sources and we found no measurement uncertainty anywhere. The margin of 0.5° is our assumption.
• The angle of the north shaft of the King’s Chamber (32.5° or 32° 36′ 08″) and those of the Queen’s Chamber shafts (39.1° to 39.6°) differ from source to source. We use 32.5° and 39.5°.
• We have not been able to check in the original articles exactly what Trimble and Badawy proposed in 1964 and what Bauval added later.
• We have not yet read the article by Wall (2007). We leave out the deviation of the shafts from true north and the course of the bent shafts.
• What lies behind the doors in the Queen’s Chamber shafts, and whether the outer openings of the King’s Chamber shafts were originally open, we have not been able to check in primary sources.
• The section is schematic. The dimensions come from one secondary source (Alison, after Petrie and Gantenbrink); the passages and the bent parts of the north shafts are not drawn.
• The building date, around 2560 BC, is the usual dating. We did not determine it ourselves.