Up becomes down. Sky becomes earth. What first appears to be a sky streaked with cloud is something else entirely: a frozen lake in northern British Columbia, seen from a helicopter above. The shadows of spruce, pine and fir trees sweep across the ice in near-perfect parallel lines. Shot in the depths of a Canadian winter, this fleeting world exists only at one precise angle of sun, for perhaps half an hour each day, before the light shifts and the shadow world disappears.