A winter view of the eastern Grand Canyon and the man-made reservoir of Lake Powell (dark blue, in the upper right of the image). This natural-colour photograph, taken from the Skylab Space Station, shows snow dusting the higher elevations. The dark, snow-free floor of the winding Canyon (left), far below and considerably warmer than the general land surface, stands out in stark contrast - a colourful indication of the three-dimensional nature of the land surface that would otherwise be hard to deduce from a vertical shot such as this.