Why are shadows never sharp?

Question

Why are shadows never sharp?

In: Physics

Answer 1

this article is about pyranometers but it has everything about the mechanics involved (see figure 13)

[Measuring sunlight: what instrument to use? (hukseflux.com)](https://www.hukseflux.com/library/measuring-sunlight-what-instrument-to-use)

The thing to be aware of is that sunlight scatters as it passes through the atmosphere, on everything it touches. clouds. the trees around you. Even clear air scatters sunlight; that’s your blue sky.

So you can think of sunlight that falls on your body as being in two buckets: (1) direct sunlight and (2) diffuse sunlight. There’s more direct sunlight than diffuse, BUT, light is coming from all directions.

All that light, even the diffuse light, casts shadows. That’s why your shadow is blurry, it’s because of diffuse sunlight. That light from many directions also casts shadow, which gives all shadows a fuzzy edge.