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		The Moon, Jupiter, an aircraft contrail, its shadow cast by the moon and a 22º ice halo. Imaged by Jean-Marie Maillard (site) of Belgium in October 2000. Contrail shadows sometimes appear counter-intuitive. This one seems cast by a low altitude bright light shining upwards and casting the contrail shadow on a higher cloud. The reverse is the case. The aircraft and its trail are high up and seen through a lower level thin layer of cirrus haze. The Moon has cast a shadow of the contrail downwards onto the haze layer. And quite independently of aircraft and shadows, ice crystals in the haze layer have created the 22º halo. Image ©J-M Maillard, shown with permission   Contrails are clouds of small water droplets and ice crystals condensed from the engine exhaust and from water vapour already in the air cooled by rarefaction over the wings and fuselage. Like other clouds they cast shadows. In the photograph the shadow falls on a thin lower layer of cirrus cloud. We see the shadow from the other side of the layer, like looking through the back of a screen. The shadow appears to the right of the line of sight between the contrail itself and the eye.