Looking up · ages 4 to 9

Why do stars twinkle?

It is one of the first space questions kids ask. Here is an answer a four-year-old can repeat, a deeper one for older kids, and an experiment you can do at the kitchen table tonight.

Lia, Leo and Pixel the robot looking up at a starry night sky
Lia, Leo and Pixel stargazing, from 100 Whys About Space.
Pixel the robot guessed first: “Stars twinkle because they are blinking at us!” Was Pixel right? Not quite.
The short answer: a star shines with a steady light. The twinkle happens near us, when moving air wiggles that light on its way to our eyes.

The longer answer for older kids

A star is a huge ball of hot, glowing gas, very far away. Its light travels in a straight line across space for years. The wiggle is added only at the very end of the trip, in the few miles of air right above your head.

All night, pockets of warm air and cool air slide past each other. Warm and cool air bend light slightly differently, so each time they move, the starlight gets a tiny nudge. By the time it reaches your eye, the point of light seems to dance and flicker. Astronomers call this scintillation.

Why don’t planets twinkle as much?

Stars are so far away that they look like single points of light, so every nudge shows. Planets are much closer and look like tiny discs. The wobbles from different parts of the disc average out, so planets usually shine more steadily. That is a handy way to spot a planet: if a bright “star” is not twinkling, it may be Venus, Jupiter or Mars.

Telescopes in space, above the air, see perfectly steady stars. That is one reason astronomers put telescopes up there.

Try it tonight: the twinkle machine
  1. Put a coin on the table behind a clear glass of water.
  2. Look at the coin through the glass.
  3. Gently poke the water with a finger.

The coin seems to wobble, but it never moved. The water moved, and moving water bends light, just like moving air does to starlight.

Your turn: pick one bright star and watch it for a minute. Does it wiggle more near the horizon? (It usually does, because you are looking through more air.)

Want 99 more space whys?

This question comes from 100 Whys About Space, a full-color Lia & Leo Explore book for ages 4 to 9: 100 real questions, a bold one-line answer for little ones, a deeper answer for older kids, and 8 try-it-tonight experiments.

See it on AmazonFree Space Explorer printables

Sources: NASA Space Place, “Why do stars twinkle?”; NASA Webb Space Telescope mission pages on observing from above the atmosphere.