Do Stars Twinkle?

You’ve heard the song Twinkle Twinkle Little Star, but is it true?

When you look into the night sky, the starlight above flickers. Set up a quick test to explore what happens to light as it travels from a star to Earth.

Catch the video below to see a walk through of this activity and hear a scientifically accurate version of Twinkle Twinkle Little Star!

What’s the Science?

When light leaves a star, the light is not moving. However, when we look up at the night sky from Earth, that same starlight seems to twinkle. The illusion of moving light occurs because of these three things:

First, star light bends as it moves through the layers of Earth’s atmosphere.

Earth’s atmosphere is made of 5 layers. The outer most layer is called the Exosphere and the air there is very thin. As you get closer and closer to Earth’s surface, the atmosphere becomes more and more dense.

When light travels from one substance to another it bends. This is called refraction. Each time starlight moves into a new layer of Earth’s atmosphere, it bends. By the time light from a distant star travels all the way from outer space to Earth’s surface, it has been refracted many times. So much so that the place we THINK we see the star is not the real position of the star!

Try This! Place a pencil in a clear glass of water. When you look at the glass from the side, what do you notice? The pencil appears broken because of refraction. Light is bending differently as it travels through the water, which is denser than the air, making the pencil look disconnected.

Second, stars are very far away from Earth.

Stars are huge, but they are so far away that we only see a little speck of light in the sky. This is true even when we look at stars through a telescope!

The effect of light refraction is much larger on a small amount of light than a big source of light. Planets, which are generally smaller than stars but much closer to Earth, do not appear to twinkle because the larger amount of light is not as visually effected by refraction. If stars were closer, they would not twinkle!

Third, Earth’s atmosphere is always moving.

In our experiment, we needed to tap our bowl of water to observe twinkling light. Earth’s atmosphere does the same thing! Air in our atmosphere is always moving and shifting, causing the distant starlight to appear to move even more than with refraction alone.

So is Twinkle Twinkle Little Star right or wrong?

To humans on Earth, stars do twinkle! But they twinkle as a result of their distance, light refraction, and Earth’s moving atmosphere. The starlight, when viewed in space, does not twinkle.

Thanks to Our Sponsors

This project is made possible by a grant from the Marie Lamfrom Charitable Foundation.