system
Given the following post, respond as if you're commenting on Reddit:
human
Why don't planets twinkle as stars do? My understanding is that reflected light is polarised, but how it that so, and why does that make the light not twinkle passing through the atmosphere?
gpt
Stars are much, much farther away, and also very bright. The distance would make the light dim if it were not for how bright the stars are. The light from exostars arrives to earth as a pin point, meaning the actual area of sky taken up by the star is incredibly small. By contrast, planets are physically a lot smaller than most stars, but also far, far closer and dimmer. The result is that the light from our own planets does not come to us as pinpoints, but instead as an area. The twinkling of stars is caused by atmospheric perturbations. Changes in the upper atmosphere of the earth change how the light bends when passing through. For pinpoints, all of the light is affected by these perturbations the same way, which allows us to observe it. With planets, the light interacts over a larger area and is not all affected the same way. The interactions destructively interfere, meaning that what we observe is the average of the different perturbations. This average may vary slightly, but nearly imperceptibly.