Ask Ethan: Why Aren’t Rays Of Sunshine P…

Ask Ethan: Why Aren’t Rays Of Sunshine Parallel?

“I understand the sun is a really long distance from the earth, such that the paths photons take that strike the earth are pretty much in parallel. So why, when I see “rays of sunshine”, produced (I assume) by the sun shining through differing cloud densities, are they radial with their point of origin being at the apparent location of the sun in our sky?”

Seen poking through a cloud, trees or other opaque materials, sunbeams are one of the most surprising natural phenomena, when you think about it. There’s always scattered, ambient sunlight in all directions, and the bright sunshine is never visible as a ray when there aren’t clouds. Moreover, the light almost always appears to diverge away from the beam’s point of origin, rather than seeming to be the parallel rays you’d expect. So why is this the case? Why aren’t rays of sunshine parallel, like you’d expect? The fact of the matter is that the rays actually are parallel, even if they don’t appear so to your eyes. 

Seeing is believing, sure, but you won’t want to miss the actual physics of what’s happening!