ABSTRACT
In another application of the time-lapse photographic method, the author examined the not very well-named Straight Wall which is, however, well-known to lunar observers because, at some 112 km long, it is an easily recognisable step in relatively level, uncluttered terrain. The overall strike of the Straight Wall is always inclined to the plane of the Sun's path and, for a short time each lunar morning, this leads to eye-catching shadows. Measuring these shadows on film that the author exposed at the Pic-du-Midi led him to estimate the heights of points, distributed along the top of the Wall, above the terrain to the west of the Wall. Digital photography has largely supplanted traditional photographic methods but lunar land profiles drawn from time-lapse studies using the methods described are still useful: even a digital time-lapse method will encounter some of the difficulties that the author have listed in connexion with the estimation of the true lengths of lunar shadows.
