Vanishing Point: Crepuscular Rays

Sun rays, also known as crepuscular rays, usually appear to converge on their source, the sun.  Crepuscular rays can also appear to come from the moon.

But sometimes they appear to come from, and converge on, a point on the opposite horizon. Known as anticrepuscular rays, their appearance of coming from some distant point on or just over the horizon is very convincing. Yet it’s an illusion. They’re actually nearly parallel beams of light.

So why do they appear to converge towards a point in the distance?  It’s all a matter of perspective.   Railroad tracks appear to converge towards a vanishing point in the distance, and painters use this concept, having parallel things converge towards a distant point to create realistic scenes.  So in this photo the light rays do connect with the hills, since they’re lit by the sun, but the light is not radiating out from them, as it appears. The hills are simply so far enough away that the more or less parallel beams of light have that illusion of convergence.

The image below was taken in the town of Wellington, looking across Smith Valley in Lyon County, Nevada.

Anticrepuscular rays over Smith Valley, Nevada.

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