Why Do Stars Twinkle

When you look at stars at night, they seem to flicker and twinkle. But stars do not really twinkle. They shine with a steady light. The twinkling happens because their light passes through Earth's atmosphere. Moving air bends the starlight back and forth, making stars appear to shimmer.

How the Atmosphere Causes Twinkling

Earth's atmosphere has many layers of air at different temperatures. Warm air and cool air bend light differently. As starlight travels through these layers, it gets bent back and forth. This makes the star look like it is jumping around slightly. The scientific name for this effect is scintillation.

Why Planets Do Not Twinkle

Planets are much closer to Earth than stars. Because they are closer, they look like tiny discs instead of single points of light. Light from different parts of the disc averages out the bending. This is why planets usually shine with a steady light and do not twinkle like stars.

Fun Facts

• Stars twinkle more when they are near the horizon because their light passes through more atmosphere.
• In outer space, stars do not twinkle at all because there is no atmosphere to bend the light.
• Astronomers build telescopes on mountaintops where there is less atmosphere to reduce twinkling.

Did You Know?

The Hubble Space Telescope orbits above Earth's atmosphere, so it never has to deal with twinkling. This is one reason it can take such sharp and clear pictures of distant stars and galaxies!