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Sputnik 1
 

   

Sputnik 1  was the first artificial Earth satellite.
The Soviet Union launched it into an elliptical low Earth orbit on 4 October 1957.
It was a 58 cm (23 in) diameter polished metal sphere,
with four external radio antennas to broadcast radio pulses.
It was visible all around the Earth and its radio pulses were detectable.