Whenever I see some fog, it usually is very opaque when I am far away, like cloud, but when I am it, it’s far more transparent, though obviously visibility is decreased
In: Physics
Fog is a cloud that is visiting the ground. Clouds are water floating in the sky that hasn’t formed droplets in order to make rain yet.
Water in any form refracts light; that is, when light hits some water, it redirects a bit. If this was a solid (or rather liquid) wall of water and you shone a light through it, you could measure a change in trajectory. The thicker the wall, the more drastic the redirection. But because the water is suspended in air in a vapor, rather than a uniform change in direction, it is a more random scattering as any given photon makes its way through air and hits water and adjusts course accordingly.
Your eyes see by absorbing light that reflects off of other objects. So combining everything: when you’re outside of the fog, you have more water being bent away from your eyes on that return trip. Since the light isn’t a constant angle when it bounces off of things inside the fog, it all scatters and mixes every which way and all the colors of light that hit the fog and reflect and refract within the fog mix together to that grey blob that fog is, unless you’re close enough to something so that the light reflecting off of it hasn’t scattered too much. Because all that scattering is effectively random, the light going in does scatter but it evens out enough that enough light hits whatever is in the fog to reflect off of it so that if you’re not having that light scatter too much on the trip off that object your brain can piece together what that light is bouncing off of.
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