Crepuscular rays are sunrays in twilight skies

What are crepuscular rays?

Crepuscular means resembling twilight or dim. This phenomenon occurs around sunrise or sunset, when the sun is below the horizon. And you can also see crepuscular rays when the sun is hiding behind clouds. They’re more noticeable when the sky is a bit darker and there is greater contrast between dark and light. We can see the rays of light thanks to dust, smoke or water droplets that scatter the light toward our eyes.

The darker streaks beside the sunrays are due to shadows, where the terrain or clouds block the sunlight from coming through. Sometimes those obstructions are below the horizon from your point of view, so it may not seem immediately clear what’s causing the darker rays.

When crepuscular rays extend from behind a cloud toward the ground, they also go by the nickname Jacob’s Ladder. The term comes from a story in the Bible where Jacob has a dream in which he sees a ladder leading up to the golden light of heaven with angels ascending and descending.

Parallel lines that seem to converge

Crepuscular rays appear to fan across the sky. But these sunrays are really parallel to each other. In fact, sometimes you can trace them all the way across the sky to the point on the horizon opposite the sunset. So, the next time you see them, remember to turn around. You might spot the fainter and less noticeable anticrepuscular rays. The illusion is similar to standing on train tracks and seeing how they appear to converge in the far distance in front of and behind you.

Photo gallery of crepuscular rays

All of these photos were contributed by EarthSky friends. Thanks for sharing your awesome photos with us! Would you like to contribute? Submit your image here.

Moon rays or moonbeams

Bottom line: Crepuscular rays are shadows in the sky of distant terrain or clouds. They form around twilight when particles in the atmosphere reflect the sun’s light beams toward our eyes. Sometimes you can see anticrepuscular rays on the horizon opposite the sun.

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