Here's why:

* Angle of Light: As the sun gets lower, the angle of the sunlight hitting the earth becomes more shallow.

* Projection: This shallower angle causes the shadow to stretch out further, making it longer.

Think of it like this: imagine shining a flashlight straight down onto a wall. The shadow will be small and compact. Now, shine the flashlight at a lower angle, and the shadow will stretch out much longer on the wall.