When you look at the blue sky, you can see some white dots flying. why is that?

 When you look at the blue sky, you can see some white dots flying.

When you look at the blue sky, you can see some white dots flying.

What you actually see is your own white blood cells (WBC).

It is the white blood cells that go in the blood capillaries in our retina that can be seen. Most of this happens in an environment with blue light.

In other places, little happens. That's why when you look at the blue sky, you can see a lot.

What happens there is that the red blood cells absorb the blue light, but the white blood cells do not.

It is the incoming light that can be seen. It is called blue field entoptic phenomena.