The Blair Cuspids

On 2 November 1966, NASA published a photograph of a region towards the western edge of the Sea of Tranquillity taken by Lunar Orbiter II (reference number LO2-61H3 [i]) at approximately 15.5ºE 5.1ºN. William Blair of the Boeing Institute of Biotechnology drew attention to a number of apparently anomalous features in the photograph, mainly a series of objects that cast long, clear shadows, contrasting them with the shorter shadows cast by objects that were more obviously boulders. Blair compared the shadows with those cast by Egyptian obelisks, causing him to suggest that the photograph shows a series of spires. Moreover, the seven objects are arranged in a geometric pattern, with right-angled and isosceles triangles. Close to the ‘spires’ was a feature that resembled an eroded rectangular trench. The photograph seems to have attracted little attention at the time, although it has been reproduced—poorly—in a number of publications. A second photograph of the site was subsequently located  by Lan Fleming (reference number LO2-62H3), taken 2.2 seconds after the first. This shows that the largest of the cuspids, number 5, is considerably broader at the base than was originally thought.

It is possible to work out the apparent height of the ‘spires’ by calculating the length of the shadow and the elevation of the sun above the horizon (which may be expressed mathematically as Height = Length of shadow × the tangent of the sun’s elevation). The largest of the objects (Cuspid 5) casts a shadow some 110 m long; given a solar elevation of 10.9º, the tallest object ought to be 21.2 m high (David Childress gives the height as 213 m!). This assumes that the lunar surface across which the shadows fall is perfectly flat, but topographical maps for the moon suggest that there is a general trend of between one and two degrees rise to the west, the direction from which the sun was shining at the time of the photograph. This means that the top of the cuspid is 21.2 m above the top of the shadow, but also that the base of the cuspid is itself up to 3.8 m higher than the tip of the shadow. The cuspid’s triangulated height should therefore be reduced by this amount, to around 17.4 m. However, that is not the only problem. These calculations also depend on the sun being a single point of light, whereas it is a disk, causing shadows to have two parts, an umbra (the region in which none of the sun may be seen) and a penumbra (the region of shadow in which a part of the sun’s disk may be seen). The angular diameter of the sun, as seen from the earth/moon system, is about half a degree, which means that the tip of the penumbra (which is what is measured as 100 m away from the cuspid) was cast by the lower limb of the sun, 0.25º lower than the 10.9º elevation already considered. Taking this into consideration, the height of the cuspid must be reduced to about 16.9 m. Furthermore, the cuspid stands on the rim of a highly eroded crater, the shadow falling into its interior. A photometric analysis undertaken by Lan Fleming suggests that the height of the cuspid is 12% of the length of its shadow, in other words 13.2 m. This makes it more or less square in profile and not at all anomalous for a lunar boulder. The remaining cuspids, all of which were suspected to be smaller, fare even less well in Fleming’s analysis.

The second frame shows a similar feature to the largest of the cuspids inside the rim of a crater, which despite Fleming’s analysis, raises the question about sloping terrain and the distortion of shadows. Indeed, it is apparent from the photographs that the shadow of Cuspid 5 falls into part of an eroded crater, identified by Blair as a rectangular trench. The trench, in fact, appears to be an optical illusion caused by the overlapping of two extremely eroded craters.

All in all, the claims made for the Blair Cuspids cannot be substantiated. Whilst their height was originally overestimated, it is evident that they are unusually large boulders, although boulders of comparable size were recorded close up by the Apollo astronauts. However, there is nothing about their recoverable shape that suggests artificiality. Their arrangement is another matter. It is undeniable that Cuspids 4 and 6 form the base of three isosceles triangles with their apices at Cuspids 1, 2 and 3, Cuspids 1, 3 and 7 form a right-angled triangle and Cuspids 4 and 5 form the base of an isosceles triangle with its apex at Cuspid 6. This might be evidence for artificiality if similar arrangements were to be found elsewhere on the moon. One can only suspect that it is a coincidence, as it does not seem to be repeated elsewhere on the lunar surface. Moreover, given the width of some of these boulders relative to their heights, claims of mathematical precision in their arrangement depend on which point on their surface is chosen for analysis. In other words, this arrangement falls well within the mathematical probabilities of occurring by chance rather than design.


[i] All satellite imagery is © Malin Space Science Systems/NASA/JPL (various dates) and is reproduced with permission.