Why do clouds have distinct edges?

[Rev. Green]

- rather than gradually fading into the sky?

[factor-fiction]

Maybe because they are a distinct mass of water vapour and a bit of dust.

[RATTER15]

Im sure they do fade into the sky but due to the distance involved you are only seeing the more dense parts of the cloud.

[bookbinder]

This might help:
http://www.scientific...do-clouds-always-appe