1 Passing clouds 
One of the pleasures of flying is seeing clouds close up. Even though they seem insubstantial they carry a considerable weight of water – around 500 tonnes in a small cumulus cloud. And water is denser than air. So why don’t clouds fall out of the sky like rain? They do. But the droplets take a long time to sink. An average cloud would take a year to fall one metre. 
2 On cloud nine 
Most of us are happy to label clouds “fluffy ones” or “nasty black ones ”, but meteorologists identify more than 50 cloud types based on shape and altitude. These fit into categories given numbers from one to nine. Cloud nine is the vast, towering cumulonimbus, so to be “on cloud nine” implies being on top of the world. 
3 Around the rainbow