Sputnik 1 (/ˈspʌtnɪk/; Russian: Спутник-1 [ˈsputnʲɪk] "Satellite-1", or ПС-1 ["PS-1", i.e. Russian: Простейший Спутник-1 "Elementary Satellite 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.
(Wikipedia)