ROCHESTER, N.Y. – You know that beautiful, clear blue sky over Rochester? It’s always a welcome sight—when it happens. But have you ever noticed the thin white streaks that sometimes crisscross the sky? Many people wonder what they are, and while they add to the beauty of the atmosphere (at least from my perspective), there’s actually a simple scientific explanation for them.

These streaks are called contrails, short for condensation trails. They are man-made clouds, formed by jets flying at altitudes of 30,000 to 40,000 feet, where temperatures can drop as low as -25 to -30°F. When jet engines burn fuel, they release hot exhaust, which contains water vapor. As this vapor meets the extremely cold air, it condenses almost instantly, forming tiny ice crystals. This process creates the visible white trails we see in the sky.

The lifespan of a contrail depends on humidity, wind speed, and direction. Some fade quickly, while others linger for a long time, spreading out to form thin, wispy clouds.

For years, meteorologists have heard conspiracy theories suggesting that contrails are actually “chemtrails”—deliberate chemical sprays released into the atmosphere for unknown but sinister purposes. However, there is no scientific evidence supporting this claim. Contrails are simply a byproduct of modern air travel and follow well-understood atmospheric physics.

So the next time you see contrails painting the sky, you can appreciate them for what they are: A natural interaction between jet exhaust and the upper atmosphere.