Take the 2-minute tour ×
Physics Stack Exchange is a question and answer site for active researchers, academics and students of physics. It's 100% free, no registration required.

There is quite foggy day today here, I cannot see end of the street. This made me think about how much worse can it be.

So here is my question: how thick a fog can be? What's the smallest visibility distance possible?

By visibility distance I mean how far I can see a black object against a white background in the fog.


There were some nitpicks, so let me clarify a bit:

  • I think of water/ice fog.
  • It's said that angular size matters, so let's say an object whose angular size as big as the full moon.
  • Whiteout doesn't count, assume the soil remains dark.
share|improve this question
Is your fog restricted to $ H_2O $ ? Just ask the Chinese how far they can see in their smog! Another nit: there's this thing called the NIIRS scale for visibility. How big is your black object, in angular space? –  Carl Witthoft Feb 7 '14 at 16:58
@CarlWitthoft I think of the usual water fog. Does angular size matter? I think of usual landscape elements: houses, trees, pylons, etc. –  Calmarius Feb 7 '14 at 17:03
Yes - rather obviously, the larger the item, the easier it is to see some sort of contrast even when badly blurred. –  Carl Witthoft Feb 7 '14 at 17:53
I am sure it can be less tham 3 meters. –  Optionparty Feb 7 '14 at 21:12
Does a whiteout (snow) count? And you're mentioning water fog, but ice fog can be much denser. –  gerrit Feb 9 '14 at 17:06

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Browse other questions tagged or ask your own question.