A top Cambridge astronomer has warned that star-gazing will be impossible by the middle of this century. Professor Gerry Gilmore said ground-based telescopes would be "worthless" if cheap air travel continues to boom and climate change increases cloud cover as predicted.

He said to reporters: "You either give up your cheap trips to Majorca, or you give up astronomy. You can't do both."

Condensation from jets - contrails - contributes to the overall murkiness of the atmosphere, Gilmore said: "The rate at which they're expanding in terms of their fractional cover of the stratosphere is so large that if predictions are right, in 40 years it won't be worth having telescopes on Earth anymore - it's that soon."

Optical and infra-red astronomy on Earth will be the casualties - radio telescopes will continue to peer through cloud cover. ®

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