Why do stars change colour when they twinkle?

In one line

The rule

The twinkling and color-changing of stars (called scintillation) happens because Earth's atmosphere bends and scatters the starlight in different ways as it moves.

Let's understand it simply

Imagine you are looking at a streetlight through a hot tandoor or over a fire. The light looks shaky and sometimes changes color. This is because the hot air bends the light in different directions. The same thing happens with starlight. The air above us is always moving and has layers of different temperatures. When starlight passes through this air, it bends, splits, and sometimes changes color before reaching your eyes.

How it works

1. Starlight travels a long distance through space, straight and unchanged.
2. When it enters Earth's atmosphere, it passes through layers of air with different temperatures and densities.
3. These layers act like tiny lenses, bending (refracting) the light in different ways.
4. Sometimes, the light bends more, sometimes less, and sometimes it splits into different colors (like a prism).
5. This makes the star look like it is twinkling and changing color, especially when it is low in the sky.

The story behind it

Long ago, people noticed stars twinkling and changing color, but they did not know why. Scientists later found that it is Earth's atmosphere that causes this effect, not the stars themselves. The word for this effect is "scintillation." Astronomers use telescopes above the atmosphere (in space) to avoid this problem.

Where you see it in real life

• Looking at stars from your terrace at night → They seem to blink and change color → This is scintillation.
• Watching a Diwali rocket's spark in the air → The light flickers and sometimes looks colorful → Air movement bends the light.
• Seeing car headlights through heat waves on a hot road → The lights look wavy and colorful → Hot air bends the light, just like the atmosphere does to starlight.
• Sunsets → The Sun looks redder and sometimes changes color as it sets → The atmosphere bends and scatters its light.

Why it matters

• Astronomers need to know about this effect to get clear pictures of stars.
• It explains why planets do not twinkle as much as stars (planets look bigger, so their light is less affected).
• Understanding this helps us learn about Earth's atmosphere.
• It is a reason why some observatories are built on mountains or in space.

Common mistakes

• Thinking stars themselves are changing color (the change happens in our atmosphere, not in the star).
• Believing all twinkling is the same (planets usually do not twinkle or change color much).
• Mixing up twinkling with blinking (stars do not turn on and off; their light just bends and splits).

Remember it

Stars twinkle and change color because Earth's air bends and splits their light, not because the stars are changing.