While you look in the (for me at the moment grey) sky, it’s almost like you don’t see just what you’d draw on a painting. It’s like a million (or so) tiny light particles flicker around. And in general it’s not like looking for example on the ground where you see everything ‚normal‘, looking at the sky feels more like watching something on an old tv.
What’s that?
In: 4
This is (probably) the [blue field entopic phenomenon](https://en.wikipedia.org/wiki/Blue_field_entoptic_phenomenon) (“entopic” means “on the inside”, in this case “inside of your eye”).
Your eye contains a bunch of blood vessels. You’ve probably seen them before at the eye doctor, when a bright light got shined into your eye, as a weird-looking web covering most of your vision. But under normal circumstances, adaptations in your eye and brain edit those blood vessels out because they’re always present. Specifically, since they’re filled with blood, they’re usually red, so your eye effectively says “okay, that area is brighter and isn’t as red as it looks”.
But once in a while, a *white* blood cell squeezes through those blood vessels. And since white blood cells are both big and, as their name implies, white and not red, they briefly let a lot more blue light through than the blood vessels normally do. So for a brief moment, the shadow of the blood vessel in your vision disappears, and the edits your eye and brain make to compensate for it make that spot look especially bright.
There are other possibilities that match what you describe, like [visual snow](https://en.wikipedia.org/wiki/Visual_snow_syndrome), but that’s the most likely reason.
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