Contrail

Aircraft contrail.
Aeroplane producing a contrail, or vapour trail, in a clear sky.

Contrails are artificial clouds formed from frozen water droplets from the exhaust of the engines of an aircraft.
They form when aircraft are flying at altitudes exceeding 5000 metres and when the upper atmosphere is nearly saturated with moisture.
In dry air the contrail quickly dissipates.

Photographed over the Cairngorms National Park, Scotland, in winter.

Location: Highland Region, Scotland.