Sputnik 1 launched on October 4, 1957.
Besides cold war speculation, this was one of the greatest events in space race that sparkled competition, scientific/technical achievements and – eventually, led to 1969 Moon Landing.
The satellite was 58 cm (about 23 in) in diameter and weighed approximately 83.6 kg (about 183 lb). Each of its elliptical orbits around the Earth took about 96 minutes. Monitoring of the satellite was done by many amateur radio operators and the Jodrell Bank Observatory. Sputnik’s R-7 booster had previously proven itself more than one month earlier as the world’s first ICBM in the successful long-range test flight of August 21 (with the accomplishment published in Aviation Week). Sputnik 1 was not visible from Earth but the casing of the R-7 booster, traveling behind it, was.
You can check some very detailed technical informations about the Sputnik satellite here: