Why do stars twinkle?
The answer lies in Earth's own air.Stars seem to twinkle because, as starlight passes through Earth's atmosphere, it is bent a little by moving pockets of air with different temperatures and densities. The light keeps alternating between reaching our eyes and veering slightly away, so the brightness seems to flicker. The stars themselves are not blinking on and off.
Wobbling air bends light
In Earth's atmosphere, air with different temperatures and densities (how tightly packed the air is) is always moving. Each time starlight passes through it, the direction of the light is bent ever so slightly. According to a NASA explanation for kids, as a result, some of the light reaches our eyes directly while some veers slightly away. This is why stars seem to flicker and twinkle.
Stars are points of light, so they wobble easily
Stars are so far away that they look like points of light with almost no size in the sky. An astronomer at the University of Wisconsin–Madison explains that starlight reaches our eyes as a thin beam, so when that beam wobbles, the star seems to twinkle. According to Encyclopaedia Britannica, the scientific name for this effect is scintillation.
Planets don't twinkle much
Planets are much closer to Earth than stars, so through a telescope they look like small disks. Light from different parts of the disk travels through the atmosphere along slightly different paths, so the wobbles average out. That is why planets usually don't twinkle as much as stars.
Stars twinkle more near the horizon
Stars near the horizon shine through more air than stars directly overhead, so they twinkle more strongly. When you look up at the night sky, try comparing stars high in the sky with stars low in the sky. You might notice the difference.
Want to know more?
- Seen from the Moon, which has no atmosphere, stars don't twinkle at all.
- The Hubble Space Telescope orbits about 483 km above the ground. Because it isn't affected by wobbling air, it can take sharper images than telescopes on the ground.
- On a clear, dark night, it is said that about 6000 stars can be seen with the naked eye.
Quick quiz: test yourself
Why do stars twinkle?
Show the answer
- The air bends their light
- The stars flicker on and off
- The stars are spinning
The air bends their light Moving air of different temperatures and densities bends starlight slightly, so the light keeps reaching our eyes and then missing them, making the brightness flicker.
Moving air of different temperatures and densities bends starlight slightly, so the light keeps reaching our eyes and then missing them, making the brightness flicker.
Next quiz ›Sources
- Why do stars twinkle?NASA StarChild (NASA Goddard Space Flight Center)
- Why Do Stars Twinkle?Encyclopaedia Britannica
- Curiosities: Why do stars appear to twinkle in the night sky?University of Wisconsin–Madison
- Why Have a Telescope in Space?NASA Science
This article was written after checking the sources above as of 2026-10-03. Explanations may change as research progresses. Photo credits are shown below each photo.
