Light can travel through some materials. Materials that allow light to pass through them are ‘transparent’. When light shines onto an opaque object, like wood or bricks, a shadow is formed.
You can make shadows yourself by shining a torch onto the wall of a dark room. An opaque object, such as a pen, placed between the torch and the wall, will cast a shadow on the wall. On a sunny day, you can see clear shadows outside. Shadows fall wherever the light of the Sun is blocked by any opaque object.
Shadows can be used to tell the time. When the Sun shines, the pencil casts a shadow onto the base of the ‘sundial’. As the Sun appears to move across the sky, the shadow falls in a different direction and points to the correct time.