What are Crepuscular rays?

Thanks to Phil KrauseCrepuscular rays, in atmospheric optics, are rays of sunlight that appear to radiate from a single point in the sky. These rays, which stream through gaps in clouds or between other objects, are columns of sunlit air separated by darker cloud-shadowed regions. The name comes from their frequent occurrences during crepuscular hours (those around dawn and dusk), when the contrasts between light and dark are the most obvious.

Crepuscular rays are near-parallel, but appear to diverge because of linear perspective. They often occur when objects such as mountain peaks or clouds partially shadow the sun’s rays like a cloud cover. Various airborne compounds scatter the sunlight and make these rays visible, due to diffraction, reflection, and scattering.

Crepuscular rays can also occasionally be viewed underwater, particularly in arctic areas, appearing from ice shelves or cracks in the ice.

There are three primary forms of crepuscular rays:

  • Rays of light penetrating holes in low clouds (also called “Jacob’s Ladder”).
  • Beams of light diverging from behind a cloud.
  • Pale, pinkish or reddish rays that radiate from below the horizon. These are often mistaken for light pillars.

They are commonly seen near sunrise and sunset, when tall clouds such as cumulonimbus and mountains can be most effective at creating these rays.

via Wikipedia

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9 Responses to What are Crepuscular rays?

  1. Steve Barker says:

    I’ve just worked out that rays of light impacting the earth from the sun will have a maximum angle of divergence of 0.0048 degrees.

  2. deskarati says:

    Have you got an App for that? Did you take into account the width of the sun, not all rays come from the same place!

  3. Steve Ashcroft says:

    I would love a copy of this picture if it’s possible. Where or who could I contact for that? (the one with the rays shining onto the lake by Phil Krause)

  4. Phil Krause says:

    I still find it hard to believe that this effect is caused by perspectives when the light is almost exactly parallel. I do know that when light passes through water vapour it forms a three dimensional shadow. Could this have something to do with it?

    • Deskarati says:

      If you look at the picture above and imagine that the clouds are not there. Surely the light would still start and finish in the same place?

  5. Phil Krause says:

    That’s my problem, I can’t imagine the rays finishing in the same place as you see in the photo. You never see crepuscular rays when there are no clouds, whys that? Remember that even allowing for the size of the sun, the rays never diverge more than one hundredth of a degree from each other.

  6. Phil Krause says:

    In photography, you can make your own star filter using a fine mess grille. This doesn’t work by perspective, it works because the light is split up into coming through separate holes.

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