Answer:
Radio beeps from a highly polished aluminium-alloy sphere barely bigger than a beachball signalled to the world, on the evening of 4 October, 1957 (GMT), that humanity had crossed a monumental threshold. We had entered the space age.
In successfully launching and placing Sputnik 1 into a low elliptical orbit, the Soviet Union took first honours in the space race. This was the stage-setting opening chapter in a saga in which scientists and their nations reached for the stars while simultaneously fearing that enemy rockets might fall upon them.