Question

When John woke up in the morning, he saw a white trail left by a plane. He wonders why he is not seeing it every time when a plane flies by. Can you explain this phenomenon to John

Answer 1

Answer:

Jets leave white trails, or contrails, in their wakes for the same reason you can sometimes see your breath. The hot, humid exhaust from jet engines mixes with the atmosphere, which at high altitude is of much lower vapor pressure and temperature than the exhaust gas.