Light and Shadows

Light is a form of energy that travels incredibly fast — about 300,000 kilometres every second — always in straight lines. The Sun is our biggest natural source of light, but we also make light with torches, candles, and light bulbs. Things that give out their own light are called light sources.

We see objects when light bounces off them and travels into our eyes. The Moon is a great example: it does not make its own light at all. It only looks bright because it reflects light from the Sun. A common mistake is to think the Moon glows by itself — it does not.

Materials behave differently when light hits them. Transparent materials, like clear glass or clean water, let nearly all the light pass straight through. Opaque materials, like wood, metal or stone, block light completely. Translucent materials, like frosted glass or tracing paper, let some light through but you cannot see clearly through them.

When light travelling in a straight line is blocked by an opaque object, a shadow forms on the other side. The shadow is the dark area where the light could not reach. Because light moves in straight lines, a shadow is always the same basic shape as the object blocking the light.

Mirrors are very smooth and shiny, so they reflect light neatly. The light bounces off at the same angle it arrived, which is why you see a clear reflection of yourself. Rough surfaces also reflect light, but they scatter it in all directions, so you do not see a clear picture.

White light is not really white at all — it is a mixture of many colours. When white light passes through a glass prism or a tiny raindrop, it splits into all its colours: red, orange, yellow, green, blue, indigo and violet. That is exactly how a rainbow is made when sunlight shines through rain.