“Why does that one blink and that one doesn’t?”
“Which ones do you mean?”
“That one up there, it’s blinking like a light bulb about to die. But that other bright one is just… solid.”
“Good eye. The blinking one’s a star. The steady one’s actually a planet.”
“Wait, stars blink and planets don’t? Why?”
“It’s not really the star’s fault. It’s actually our own air playing tricks on us.”
“Our AIR does that?”
“Yep. Starlight travels for years, sometimes centuries, before it reaches us. By the time it gets here, it’s basically one single, perfect point of light hitting your eye.”
“So?”
“So when that one tiny point finally punches through our messy, moving atmosphere, all those layers of warm and cool air swirling around, it gets bounced around just slightly. Bent one way, then another.”
“So it LOOKS like it’s blinking, but it’s actually just… us? Our air?”
“Basically. The star itself is shining perfectly steady, the whole time.”
“Then why doesn’t the planet do that too?”
“Because a planet’s actually really close to us, relatively speaking. Close enough that it’s not one single point, it’s technically a tiny little disk, even if your eyes can’t quite tell.”
“So it’s not just ONE point of light?”
“Right, it’s like hundreds of tiny points bundled together. When our messy air jiggles one of them, all the others are still holding steady. It kind of averages out. So the planet just glows calm and steady.”
“So the blinky one is actually really far, and the calm one is actually pretty close?”
“Exactly backwards from what you’d guess, right?”
“So the flashiest, blinkiest lights in the sky are actually just quietly telling on themselves, that’s how you know they’re really, truly far away.”
Now It’s Your Turn
Find someone tonight and see what you both remember.
- What actually causes stars to twinkle?
- Do planets secretly twinkle too, up close?
- How can you tell a star from a planet just by looking?
(Whenever you’re ready: 1. Earth’s moving atmosphere bending a tiny point of light. 2. No, they’re really many points of light bundled together, which cancels out the wobble. 3. Twinkly usually means star, steady usually means planet.)
Maybe tonight, find one light that twinkles and one that doesn’t, and guess which is which before you check.
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