James Houston (Member 63,170) spotted a burst of rays emanating from Altocumulus clouds over the skyline of Vancouver, Canada. The rays of light and shadow show up like this when the sunlight is scattered by atmospheric haze in the air beneath the clouds. Such rays are always present when clouds obscure the sunlight, but we only see their paths when the light’s scattered – like the beam of a projector in a cigar-smoke-filled movie theatre of old.

Where the analogy of a movie projector breaks down is how the light fans out like this. While the beam projecting the flickering image of the silent movie splays out due to the projector’s lens spreading the light across the screen, crepuscular rays like James’s do not in reality spread out at all. In fact, light rays from our distant Sun are almost completely parallel. They only appear to fan out due to the effect of perspective. In the same way, the projector beam would also appear to fan out much more if you stood up and looked into its dazzling light. Hey, can you sit down, please – you’re casting a shadow on the screen.