The contrail was moulded by winds - shaping its unusual right angles
But those looking for a sensational or supernatural explanation for the water vapour suspended in the shape of Aladdin's flying carpet are set to be disappointed. A Met Office spokesman reassured residents that the cloud just an oddly-shaped contrail - the man-made clouds formed by the water vapour blasted from a plane's jet engine as it moves through the air. But while contrails normally appear as two thin stripes tracing a plane's progress through the sky - a mixture of atmospheric conditions transformed this example into a floating rectangle.
The Met Office spokesman said: "In this case an aircraft has moved through a pocket of air with the right conditions for the contrail to form, meaning there is just a short section. The wind is blowing at right angles to the contrail, and due to the right atmospheric conditions this is causing the ice crystals in that trail to spread outwards - creating this rectangular shaped cloud.
It's unusual to see the cloud edges quite so well-defined as in this example but the processes involved are very common"
http://www.sott.net/article/283035-Bizarre-square-cloud-photographed-over-Exeter-UK