Why do I see my shadow on the sidewalk on a sunny day?
Whenever light hits an object, it casts a shadow. A shadow forms when an object blocks light from its light source, creating an area behind the object that the light cannot reach. A screen placed behind the object will be dark where it lies in the shadow. When you stand on the sidewalk, the screen is the cement surface on which you are standing. The Sun is your light source. As the Sun moves in the sky, the shadow—since it is the part of space “behind” you as viewed from the Sun—will move as well. Because the sidewalk touches your feet, the shadow will always form an image connected to your feet. It will extend from there in a direction opposite to the direction to the Sun. When the Sun is in the East, in the morning, the shadow will extend to the West, and when the Sun is in the West, in the evening, the shadow will extend to the East.