Shadows and the Sun

A shadow forms when an opaque object blocks light. Light travels in straight lines, so it cannot bend around the object, and a dark area forms behind it. A shadow has the same outline shape as the object. Transparent objects make almost no shadow; translucent objects make a faint one.

Shadows change size. Moving an object closer to the light makes its shadow bigger. During the day the Sun seems to move across the sky because the Earth spins. In the morning and evening the Sun is low and shadows are long. At midday the Sun is highest and shadows are shortest. A sundial uses a shadow to tell the time.