Grade 5 · Unit 4: The way we see things

Light travels from a source

We see things when light enters our eyes.

The Sun is our most important light source.

Light sources

A light source gives out its own light. It is luminous. The Sun, stars, fire, lamps and screens are light sources. Most things we see are not light sources – they reflect light.

Some animals are light sources too. Fireflies and some deep-sea fish make their own light through a chemical reaction.

How we see

Light travels from a source in straight lines. It hits an object and some of it bounces off. The reflected light enters our eyes, and we see the object.

We see coloured objects because they reflect some colours of light and absorb the rest. A green leaf reflects green light.

Drawing rays

Scientists draw light as straight lines called rays. Arrows on the rays show the direction the light travels. Rays go from the source, to the object, to the eye – never from the eye.

Long ago, some people thought eyes sent out rays to see things. The scientist Ibn al-Haytham showed about 1,000 years ago that light comes into our eyes.

The Moon shines?

The Moon is not a light source. It looks bright because it reflects light from the Sun.

The Moon’s phases change because we see different amounts of its sunlit side as it orbits the Earth.

What I learnt