Why do stars change colour when they twinkle?

In one line

The rule

Stars appear to twinkle and change colour because their light passes through Earth's atmosphere, which bends (refracts) the light unevenly, causing quick changes in brightness and colour.

Let's understand it simply

Imagine you are looking at a Diwali rocket far away through the hot air above a tandoor. The rocket looks shaky and sometimes changes colour. This is because the hot air bends the light in different directions. The same thing happens with starlight. When you look at a star, its light travels through layers of air. Each layer can be hotter, colder, or moving. This makes the light bend (refract) in many ways. Sometimes, the light spreads out into different colours, like a mini rainbow. That is why stars seem to twinkle and change colour.

How it works

1. Starlight travels a long way through space, which is empty and clear.
2. When the light enters Earth's atmosphere (the air around us), it passes through many layers of moving air.
3. Each layer bends the light a little differently (refraction).
4. Sometimes, the bending splits the light into colours (like a prism).
5. This makes the star look like it is changing colour and brightness quickly.

The story behind it

Long ago, people noticed that stars twinkle but planets do not. Scientists later found out that this is because stars are so far away, they look like tiny points of light. Their light is easily disturbed by the air. Planets look bigger in the sky, so their light is steadier. The study of how light bends in air is called atmospheric refraction.

Where you see it in real life

• Looking at stars on a hot summer night → stars seem to dance and change colour → this is because of the moving air.
• Seeing a coin at the bottom of a well → the coin looks bent or shifted → light bends in water, just like starlight bends in air.
• Watching a Diwali rocket through smoke → the rocket looks shaky and colourful → smoke bends the light, just like the atmosphere.
• Rainbow in the sky → sunlight splits into many colours by raindrops → starlight can also split a little in air.

Why it matters

• Helps astronomers understand why stars twinkle and how to get clearer pictures using telescopes.
• Explains why stars look different from planets in the night sky.
• Shows how our atmosphere affects what we see in the sky.
• Important for science exams and for understanding weather and light.

Common mistakes

• Thinking stars themselves are changing colour → actually, it is Earth's air causing the effect.
• Believing planets twinkle just like stars → planets usually shine steadily because they appear bigger.
• Mixing up twinkling with blinking → twinkling is a fast, random change, not turning on and off.

Remember it

Stars twinkle and change colour because Earth's air bends their light in many ways, like looking through moving water.