On a warm night this summer on Edisto Island, SC, my friends and I took to the beach to go shrimping. The after-dark escapade turned into a feeding frenzy, reaping monstrous crustaceans with beady, red eyes. The younger kids eventually took turns in the water, and I sat on a sand dune and looked up at the clear sky. I could make out the outline of our galaxy, thousands of stars, and what I thought might be planets.
Planets don’t twinkle, right? Stars do. But satellites definitely blink. Wait, what’s the difference between twinkling and blinking? Maybe if I stop blinking my eyelids I’ll be able to tell.
I sat on that dune for two hours trying to figure out which white dots in the sky were stars or planets, based on whether they scintillated or not.
What I didn’t understand is that, in reality, stars don’t twinkle at all.
Light penetrates Earth’s atmosphere and makes its way toward us. Yet, the way down is a pretty bumpy ride, all because our atmosphere is so alive. “Turbulence” occurs when the air above us is constantly moving and mixing in different ways. The light we see from stars and planets gets twisted in that turbulence, hence our “twinkling” or shaking image of stars. The longer the light has to travel through Earth’s atmosphere to get to you, the more chance the light has to experience turbulence, and the more twinkly it might be. Then why doesn’t everything we see twinkle? Our Sun doesn’t blink or vibrate in the sky, and that’s because its angular size is very big compared to that of stars far away from Earth. Similar reasoning explains why planets, to the naked eye, don’t seem to twinkle (or experience scintillation) as much as stars. Planets also have a significant angular size from our point of view, so they stay pretty still. Though it’s less poetic to say, stars don’t twinkle – our atmosphere just jiggles.
