Corrugated Shadows

Last updated on September 16, 2023

Corrugated Shadows: Unraveling the Mysteries

Shadows have always captivated our imagination with their enigmatic qualities. One particular type of shadow that piques our curiosity is the corrugated shadow. These shadows possess intriguing features that beg for an explanation. In this article, we will delve into the mesmerizing world of corrugated shadows and attempt to unravel their mysteries.

Two Superimposed Shadow Types

When observing corrugated shadows, we are actually witnessing the interplay of two distinct types of shadows. The first type is a 2D ridge shadow cast onto the opposite valley wall. If you mentally flip the small insert image, you can align it with the shadow features. The second type is a series of solid, 3D shadows cast into the air itself. It is these three-dimensional shadows that give rise to the captivating characteristics we observe.

The Dark Void of Shadowed Air

The air within the shadowed region appears as a dark void. At its top, parallel corrugations can be observed, corresponding to the profile of the ridge. To visualize this, try creating parallel folds in a sheet of paper. The camera captures these corrugations as it follows the sharp fold originating from the pinnacle top, represented by the red spot in the diagram.

Shades of Blue in Shadows

Have you ever wondered why corrugated shadows exhibit various shades of blue? The answer lies in the path of our line of sight along the shadow of the pinnacle. As we gaze across to the parallel shadow of an adjacent peak, our line of sight traverses sunlit air. The scattered light from this sunlit air brightens the appearance of the shadow. Consequently, the shadow of the next peak appears even lighter due to two bands of intervening sunlit air.

The Knife-Like Pinnacle Shadow

In contrast to the 2D ridge shadow on the valley wall, the dark shadow we observe in the air is a 3D air shadow. From the red spot mentioned earlier, the pinnacle's 3D shadow void manifests as a sharp wedge shape. This knife-like appearance adds to the mystique of corrugated shadows.

Convergence of Shadow Edges

If you closely examine the uppermost ridges of the shadows, you will notice that they are parallel. However, from the perspective of the red spot, these ridges appear to converge towards the antisolar point, which is directly opposite the sun. This point is marked by the shadow of the pinnacle peak on the opposite valley wall, indicated by the blue spot. To experience this phenomenon firsthand, try looking along a parallel folded sheet of paper with your eye positioned at the red spot.

Unveiling Nature's Artistry

Corrugated shadows showcase nature's artistic prowess, offering us a glimpse into the intricate interplay of light and shadow. By unraveling their mysteries, we gain a deeper understanding of the atmospheric optics at play. The ethereal shades of blue, the knife-like silhouette, and the convergence of shadow edges all contribute to the captivating beauty of these unique phenomena.

Conclusion

Corrugated shadows have fascinated observers for centuries. Their complex interplay of 2D ridge shadows and 3D air shadows creates a visual spectacle that challenges our understanding of light and perception. By studying these shadows and their characteristics, we can unlock the secrets of nature's artistry and gain a greater appreciation for the wonders that surround us. So next time you find yourself in the presence of corrugated shadows, take a moment to marvel at their enigmatic allure and embrace the beauty that lies within.

The pinnacle of Aguille de la Tsa, casts its morning shadow across a valley. Imaged in the Swiss Valais by James Osborn August '07 from the pinnacle top (see lower insert view) . Large image ©James Osborn, insert summitpost.org.

The shadows have several intriguing features. Why are they several shades of blue? Why is the pinnacle shadow knife-like and inky dark? Why do the shadow edges converge towards the tip of the pinnacle shadow?

We are looking at two superimposed shadow types. The first is the 2D ridge shadow cast onto the opposite valley wall (mentally flip the small insert image left to right to match the shadow features). The second series of shadows are solid, 3D, cast into the intervening air itself. It is these that create the interesting features.

The shadowed air is a dark void. Its top has parallel corrugations corresponding to the ridge profile. Make some parallel folds in a sheet of paper to model it. The camera sees the corrugations from the sharp fold coming from the pinnacle top - the red spot in the diagram.

Shadow blues - Look from the red spot along the shadow of the pinnacle. All the air in the path is in complete shadow and is dark. Look across to the parallel shadow of the adjacent peak. Your line of sight crosses intervening sunlit air. Scattered light from the sunlit air lightens the appearance of the shadow. The next peak's shadow is lightened even more by two bands of intervening sunlit air.

Sharp pinnacle shadow - the dark shadow is in the air. it is a 3D air shadow, not the 2D one on the valley wall. From the red spot the pinnacle's 3D shadow void appears as a sharp wedge shape.

Converging shadow edges - The uppermost ridges of the shadows are all parallel. But from the red spot they appear, by perspective, to converge on the antisolar point directly opposite the sun and marked by the shadow of the pinnacle peak on the opposite valley wall (blue spot). To see the effect 'live' try looking along a parallel folded sheet of paper with your eye at the red spot position.

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Reference Atmospheric Optics

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