Why the solar eclipse caused such fascinating shadows to appear on the ground

The solar eclipse captured the imagination and gaze of millions across the United States, but for some it was what was on the ground rather than in the sky that was fascinating.

Take a look at this video taken in Oklahoma for example.

What David Montero here had spotted was that the moon’s passing between Earth and sun affected the shape of shadows caused by our star – but only in certain conditions.

So why were these crescent-shaped shadows only available through tree tops? Well, another person who spotted the phenomenon had the answer.

Jayme Fraser rightly suggested the small gaps between the leaves act as pinhole cameras – causing the image of the sun to appear on the ground as if from a projector.

Light passing through a small point causes a projection of the light from the other side to appear upside-down on the other side – in a quirk of physics known as the camera obscura effect.

What people have been seeing then are inverted versions of the image of the sun which they could see in the sky, if say they were to look at it through protective glasses.

This concept of a pinhole camera is in fact the basic principle on which a human eye works, minus a lens, aperture and other enhancing details – but the human brain automatically flips the image so we experience it the right way up.

So, for those of you a little disorganised and caught out with no protective glasses next time there’s an eclipse, find yourself a suitable tree and try looking down instead of up.

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