How come shadows get blurrier the farther it is from an object?

Question

The contact point in which the shadow touches the object is way sharper than say 5 metres from the object that’s casting a shadow. How come?

In: Physics

Answer 1

Because the sun is not a point source; it has a visible disc. That means that the light from the sun doesn’t come from exactly one direction but from a small range of directions. So shadows due to the sun have blurry edges to match the apparent size of the sun, which as about half a degree across. The farther the shadow from the object that’s casting it, the larger the burred region caused by the half-a-degree angle. The same effect works for other lights that cast shadows too. If you want sharp shadows, use a tiny light source; you can use a lens instead, like a projector, but then you have to focus.