Matrix...

I feel sorry for your students.

I wish all you people would apply logic. What you see in the sky is just water vapour. I have a masters degree in thermodynamics, so I'd know.

The liquid sprayed is precooled so as to prevent any vapor formation. What I'm telling you, and this is correct (from my personal experience) is that any liquid sprayed from planes (also NOT commercial planes, spraying is strictly a military operation) is invisible.