converging shadows
Home page

Fig. 1 - Apollo 11 commander Neil Armstrong photographs Tranquility Base from some distance behind the lunar module. (NASA: AS11-40-5961)

In Fig. 1 the photographer's shadow falls directly away from him, but the shadows of the rocks in the lower right fall at an angle, and some of them seem to fall almost horizontally. Since the light rays from the sun are parallel, the shadows must also be parallel. Clearly this was photographed using several artificial lights.

See the detailed discussion about perspective through the camera. While it's true that the shadows cast by sunlit objects are roughly parallel over flat, level ground, it is not true that they will always appear parallel when photographed. In fact, they will appear parallel to the eye or camera only under very special circumstances.

Fig. 2 - Converging shadows of objects lit by the sun. A combination of terrain and perspective produces shadows in the upper right of the image that appear to lie almost at right angles to the shadow of the photographer.

An easily-seen feature of perspective is its tendency to make shadows appear more horizontal the farther they are away from the viewer. This affects many of the photographs conspiracists say show anomalous shadows.

Fig. 3 - The close-up surface camera resting at an angle. Its handle casts the narrow foreground shadow in Fig. 1. (NASA: AS11-40-5957)

In a real photograph, perspective requires the shadow to point to the photographer's feet, which must be underneath the horizontal center of the frame. [Colin Rourke (Aulis PDF), after Jack White and John Costella]

Neither Rourke nor White and Costella before him offers any sort of example, argument, computation, or line of reasoning for this assertion. In fact there is no such "rule" of perspective. Figs. 2 and 4 were specifically taken to address this claim and show photographer shadows that align with the left edge of the frame.

Yes, terrain and camera rotation affect the appearance of the shadow, but the terrain here is flat and the cammera cannot be rotated because it is fixed to the "breastplate." [Rourke, Ibid.]

No, this famous photograph was taken from the rim of Little West crater. The ground slopes downward and away to the left. What Rourke inaccurately calls the "breastplate" is the RCU, the remote control unit for the space suit equipment. Contrary to popular belief, it hung loosely from the backpack straps on two hooks. There was ample play in the mounting hardware to aim the camera.

Perspective cannot explain the extreme angle of the shadow at bottom center.

Probably not, but in analyzing photographs one cannot presume that the object casting it is perfectly vertical. Objects will only cast parallel shadows if they themselves are parallel along the line of illumination. As seen in Fig. 3, which was taken just prior to Fig. 1, the close-up surface camera, whose handle is casting the shadow in Fig. 1, is tilted at an angle.

There is a peculiar halo around the shadow of the astronaut's head. This is obviously a "hot spot" caused by studio light meant to emphasize the shadow.

It would be strange to introduce such an artificial lighting scenario in a photograph intended to depict a natural circumstance. In fact the "halo" is the response of the textured lunar surface to a phase angle of zero. At that point in the photograph, the photographer is looking right down the direction from which the light is coming, hence his shadow. The shadows of objects -- rocks, craters, grains of dust -- are being hidden by the objects themselves.

This, instead, confirms that sunlight is the only significant source of light in this photograph. You do not get such phase-dependent effects from studio lighting of any kind.

Fig. 4 - An approximation of Fig. 1 reproduced on earth. The surface is six-month-old asphalt concrete. Note the shadows of rocks placed by the photographer at upper right and the shadows of the nearby cars.

Fig. 5 - The same photo as Fig. 4 modified to amplify the contrast. This has the effect of darkening shadows in order to better approximate the stark shadows of the lunar surface. Note the halo around the shadow of the photographer's head.
Figures 4 and 5 depict a rough reconstruction of Fig. 1, photographed using only sunlight on a reasonably flat and level surface. (It is obvious that the surface in Fig. 1 is neither flat nor level.) The sun elevation was approximately 12°, or approximately 3° higher than at Tranquility Base.

Fig. 5 has been modified by adjusting the contrast digitally. This artificially amplifies the difference between light and shadow. Because scenes on Earth are also lit by light scattered by the atmosphere, it is impossible to duplicate exactly on Earth using only sunlight the lighting conditions on the moon. This contrast-enhancing technique gives more visual emphasis to shadows cast directly by the sun and de-emphasizes the effect of scattered light. It is not intended to exactly duplicate sunlighting on the moon.

Notwithstanding the inaccuracy of the approximation, the same optical principles produce a "halo" around the photographer in Fig. 5, for the same reason. The roadway is textured according to normal asphalt concrete construction, and at low sun angles the shadows cast by elements of that texture have a cumulative effect that is increasingly visible as phase angle increases. At a phase angle of 0°, none of those shadows can be seen, and the cumulative effect is that of a zone of increased brilliance.

It's not just an optical illusion. There actually is more lighting reaching the camera from that part of the surface than from other parts. This is the "zero phase angle effect" which renders the full moon four times brighter than a half moon, as seen from earth.

The camera is tilted downward in Figs. 4 and 5 more than in Fig. 1. In Fig. 1 the optical axis is at a shallower angle than the illumination angle. In Figs. 4 and 5 the optical axis is deeper than the illumination angle. Nevertheless a reasonably representative set of lines of sight can be correlated between the photos.

Prev Next