Mont Blanc Shadow & Spike

Jakub Badelek (photography) took this image of his fellow climbers Remek, Tomek and Lukasz.   Mont Blanc at 4810m is the highest of the Alps. The freshly risen sun casts a miles long shadow tube from the mountain towards the antisolar point.  Perspective makes the darkened air appear as a triangular apparition.
    All images ©Jakub Badelek, shown with permission
A non-intuitive shadow spike jets upwards and leftwards from the top of the mountain shadow.

The near full moon slides downwards in the west.

Shadow spikes appear when climbers are below the summit.

Imagine the mountain sliced in two at the climber's level. The mass of rock beneath casts a long shadow. Looking along and through it makes it appear as the 'conventional' triangular mountain shadow with its point upwards.

What about the mountain slice above the climber? It too casts a long shadow tube just like the lower mountain. When the eye looks along it, the upper shadow also has a triangular shape - but pointing downwards. If the summit is to the right then there will be a stronger spike in that direction.

Alternatively, think of the mountain above as a rather weighty cloud casting anticrepuscular rays!

To see a substantial upper shadow spike the climber must be at some distance below the peak.  Jakub and his companions were at that point only about 250 m below the summit - hence the faint spike.

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The shadow is almost parallel. Perspective makes it appear to converge to a point when it is viewed from the mountain. The climber is then looking along its length.

Imagine standing in a long corridor - the geometry is the same.