Residents of Exeter posted photos on Facebook and agitated Twitter messages about the flying carpet cloud hanging over the city.
The sharp-edged cloud formation was first spotted Saturday afternoon, but the hype was tweeted by Laura Gilchrist, a Met Office employee.
Tweet from Met Office employee Gilchrist: "A diamond cloud was seen over Exeter this evening."
But those looking for sensational or supernatural explanations will be disappointed. A Met Office spokesman assured residents that the cloud is simply a strangely formed contrail - an artificial cloud formed by water vapor from an airplane's jet engine as it moves through the air.
True, inversion clouds usually appear as two thin stripes diverging in the sky, and in this case, the combination of unusual atmospheric conditions has transformed the emissions from the engine into a floating rectangle.
A Met Office spokesperson said, "In this case, the aircraft was passing through an air pocket where conditions were created to form a rectangular inversion shape, it was a very brief moment."
»The wind was blowing at right angles to the contrail and this resulted in the correct atmospheric conditions. The movement of air caused ice crystals in this trail to spread outward, creating a rectangular cloud.
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"It is unusual to see a cloud with sharp edges as in this example, but the processes involved in the formation of the flying carpet are very common."