A shadow forms when an object blocks light from reaching a surface.
That sounds simple, but the size of the shadow can change dramatically depending on where the light source is, where the object is, and where the shadow lands.
The Sun changes angle during the day
Early in the morning, the Sun is low in the sky.
Sunlight reaches you at a shallow angle.
Your body blocks that angled light, so the shadow stretches a long distance across the ground.
Near the middle of the day, the Sun is much higher.
The light comes down at a steeper angle and the shadow stays closer to your feet.
Later in the afternoon, the Sun drops lower again and shadows grow longer.
Why can a small object make a huge shadow?
Put a small object close to a lamp and far from a wall.
The object blocks a wide cone of light before that light reaches the wall.
Its shadow can become much larger than the object itself.
Move the same object close to the wall and farther from the lamp, and the shadow usually becomes smaller.
Nothing about the object changed.
The geometry did.
Does distance from the light always matter?
Yes, although the effect depends on the kind of light source.
A nearby lamp behaves differently from the Sun because the lamp is much closer and light spreads outward strongly from it.
The Sun is so far away that its rays reaching a small area on Earth are nearly parallel.
That is why moving your hand a few inches toward the Sun does not make the same dramatic difference as moving it toward a desk lamp.
Why do shadows sometimes look blurry?
Real light sources have size.
A large light source sends rays from many slightly different directions.
At the edge of a shadow, some rays may be blocked while others still reach the surface.
That creates a softer edge.
A small or distant light source tends to make sharper shadows.
Can a shadow be bigger than the object?
Absolutely.
It can also be smaller.
The result depends on the positions of the source, object, and receiving surface.
This is the same basic reason hand-shadow puppets can grow or shrink on a wall as you move your hands.
Why do your shadows point in different directions?
The shadow forms on the side opposite the light source.
As the Sun appears to move across the sky, the shadow rotates around the object.
So your shadow is not stretching because it had a long day.
It is just geometry responding to where the light happens to be.
A related explanation is Why does a straw look bent in water?, which looks at another familiar effect from the same general system.
And that’s the short explanation.
Related explanations: Why does a straw look bent in water?, Why do mirrors reverse images?, and Why do we see lightning before thunder?