I have been told that darkness is better to use than blackness; that blackness is not correct.
But what about this intellectual giant Carl Sagan here (0:52):
He said "blackness" with the stress on that word and he certainly is aware of English.
So, my question is: why couldn't I use the word blackness instead of the word darkness if it is more logical (reference to the black color instead of vague dark which can also be dark-brown, dark-red etc.) and Carl Sagan use it too?
I am really curious about that, because when I used word "blackness" on several occasions people smiled at me and told me it is wrong.
Is it OK to use that word in the academic world and just stay away from it when dealing with casual people who speak English?