Captain Eugene A. Cernan, Apollo 17 Mission Commander, said Neil Armstrong was a "world icon, a nation hero of unimaginable proportion, and a legend whose name will live in history long after all here today have been forgotten."
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Temperatures will remain close to freezing.
The prime minister's announcement came as international leaders gather in Paris on the second anniversary of the climate change plan.
Prime Minister Theresa May said in October the Government will shift towards an organ donation system in England which presumes consent.