You’ve probably looked up one clear morning and seen those long white lines streaking behind an airplane. Sometimes they intersect, as if someone were playfully tracing secret patterns against a bright blue background. Why do they appear some days and vanish just as quickly on others? Behind these luminous streaks lies a very real phenomenon… but the key to the story is never what you’d expect at first.

Where do the white trails of airplanes really come from?

The starting point is actually quite simple: when an airplane flies at high altitude, the air is extremely cold and dry. At the same time, the engines release hot steam which, upon encountering this intense cold, instantly transforms into tiny ice crystals. It’s a bit like when your breath becomes visible in winter: the same magic, but on a much larger scale.

These tiny crystals reflect sunlight, which explains their brilliance and pristine white color that gives the impression of delicate brushstrokes in the sky. They are nothing more than small, ephemeral clouds, created by the passage of airplanes.