If you've seen videos of airplanes taking off or landing, you may have spotted something shocking: what appears to be smoke trailing off the wings of landing planes. The good news is that vapor is certainly not smoke—it's wake turbulence.
“The smoke-like appearance is the result of compressing gas into solid (moist air into water vapor),” commerical airline pilot Chris Cooke tells Travel + Leisure. “The more relative humidity there is, the more vapor you'll see. In most circumstances, wake turbulence and wingtip vortices are invisible to the naked eye. When atmospherics are favorable, those vortices will be visible for a short period of time.”
Related: What Exactly is Turbulence?
And though the wake isn’t dangerous for the plane creating it, it can cause some problems if another plane gets too close, especially a smaller one. “It can be dangerous to follow too closely behind an aircraft due to wingtip vortices and wake turbulence,” adds Cooke. “Large commercial aircraft are always separated during takeoffs and landings due to the danger of wake turbulence created during the creation of lift. ... It takes a few minutes for those vortices to dissipate. Sometimes, you can be flying along and feel a jolt because you've come across somebody's old wake, just like a boat on the lake.”