Video posted by the rebel forces shows a jet framed in a cloudless sky being shot at, catching fire and falling out of frame.

CNN: STORY HIGHLIGHTS

But there might be an even more animalistic explanation why a cloudless sky buoys us up: "When it's good weather there's much more flesh on show, which cheers most people up, " says Dr Workman.

BBC: Call that a summer?

But a clear, cloudless day-time sky is blue because molecules in the air scatter blue light from the sun more easily than they do red light.

BBC: rainbow

The sky is still a perfect cloudless blue and the forecasters have dropped their previous prediction of rain by the weekend.

BBC: US crops tell story of future world food prices

A. hospital, sending nicotine clouds into the cloudless sky, wondering whether it would be better to have one leg and no arms or, if you were lucky enough to have an arm and a leg left, whether it would be better to have them on opposite sides, for balance.

NEWYORKER: The Visitor