When you gaze up at the night sky, you’ll notice that stars appear to twinkle, while planets shine with a steadier glow. This charming shimmer has inspired poetry and songs, but the reason why stars twinkle is rooted in physics and our atmosphere. It’s not the stars themselves that are changing, but rather the way their light travels to us.
What Is Twinkling?
The scientific term for twinkling is stellar scintillation. It refers to the rapid changes in brightness and position of a star’s light as seen from Earth. These changes happen because starlight is distorted as it passes through the layers of Earth’s atmosphere.
This effect is most noticeable when stars are near the horizon or when the air is especially turbulent.
The Role of Earth’s Atmosphere
As starlight travels through space, it moves in a straight line. But once it hits Earth’s atmosphere, it encounters different layers of air with varying temperatures, densities, and moisture levels. These air layers constantly shift, bending the light in multiple directions through a process called refraction.
This causes the star’s light to jiggle slightly and vary in brightness as it reaches your eyes, giving the appearance of a “twinkle.”
Why Planets Don’t Twinkle (As Much)
You might notice that planets shine more steadily than stars. That’s because stars are extremely far away and appear as tiny points of light. Even slight changes in air cause noticeable flickering.
Planets, on the other hand, are closer and appear as small disks in the sky. The light from a disk averages out more as it passes through the atmosphere, so the twinkling effect is greatly reduced or not visible at all.
Twinkling and Star Colors
Sometimes, twinkling stars seem to change colors—flashing red, blue, or green. This happens for the same reason: the atmosphere bends different wavelengths of light differently, especially when stars are low in the sky. It’s not the star itself changing color but the atmosphere playing tricks on your eyes.
Where Twinkling Disappears
If you were to leave Earth’s atmosphere—say, aboard a spacecraft—the stars would stop twinkling entirely. In space, without air to distort the light, stars shine steadily and clearly. That’s why space telescopes like Hubble capture such sharp, detailed images of distant stars.
Glossary
- Stellar scintillation – The scientific name for the twinkling of stars.
- Refraction – The bending of light as it passes through substances of different densities.
- Atmosphere – The layer of gases surrounding Earth.
- Wavelengths – The distances between peaks in waves of light, which determine color.
- Disk – The round shape of a planet as seen from Earth, as opposed to a point.
