The streaks of light and shadow that often accompany Wyoming sunrises and sunsets have a name — crepuscular rays.

Stemming from the Latin “crepusculum,” meaning twilight, the sunbeams can appear at any time of day, but are most noticeable as the sky changes at dawn or dusk, as photographed on Tuesday evening in Laramie. 

Sunlight shooting through gaps in clouds or other features of the horizon causes the optical phenomenon, while tiny particles like dust, water vapor or pollen, suspended in the air, scatter the light, making it visible to our eyes. 

Though the beams appear to fan outward from the sun, crepuscular rays are parallel. It’s similar to how lines on a highway or railroad tracks appear to narrow in the distance. 

The next time you spot crepuscular rays, turn your back to the sunset for a chance to see a more elusive phenomenon. Though less vibrant, anticrepuscular rays appear in the opposite direction of the sun and can give the effect of the horizon being cut in half, visible in the photo below. 

Anticrepuscular rays appear in the opposite direction of the sun and can give the effect of the horizon being cut in half, as pictured the evening of July 29, 2025 in Laramie. (Maggie Mullen/WyoFile)

Maggie Mullen reports on state government and politics. Before joining WyoFile in 2022, she spent five years at Wyoming Public Radio.

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