eli5 Why does light around stars flicker when you look at them in the night sky?


eli5 Why does light around stars flicker when you look at them in the night sky?

In: Physics

Same reason the bottom of a pool dances around and flickers when you look at it from above the water. The star’s light passed through the layers of our atmosphere which makes it dance around a little bit.

Atmospheric shimmer.

The atmosphere isn’t static, and isn’t *perfectly* transparent. Different densities, wind currents, small dust particles, etc etc all add up to make light shift around slightly as it passes through.

This is why space telescopes are so useful, it eliminates this concern

One of my favourite scientific terms: atmospheric scintillation

You know the heat haze you get above a fire/radiator/hob? That’s because air at different temperatures can cause light to bend (refract).

The atmosphere has lots of small pockets of air with slightly different temperatures, and they’re all swirling and bubbling around each other, constantly moving. When you look at a star, there is a ray that should reach you as the light shines through the atmosphere. Sometimes, the atmosphere shifts in such a way that the ray misses you completely. This makes it briefly flicker out for a second. Then another instant, a ray that should miss you gets bent towards you and it looks extra bright for a second. This is why they twinkle.

Planets are big enough in the sky (because they’re much closer) that this shimmer doesn’t usually make them blink out. Instead, they just jitter about slightly, which is easier to see through a telescope. The moon can be seen in enough detail that you can really see the heat haze effect on the craters.