Amateur astronomers observing Sputnik 1 from Kazakhstan. Sputnik 1, the world's first artificial satellite, was launched by an R-7 Semyorka rocket from Tyuratam military range (now Baikonur Cosmodrome), Kazakhstan, on 4 October 1957. The satellite consisted of an aluminium ball, with a diameter of 58 centimetres, carrying four whip-like antennas. It weighed 83.5 kilograms. It orbited the Earth at a height of 250 kilometres for 21 days, gathering information about the electron density of the ionosphere. The launch of Sputnik 1 prompted the USA to enter the Space Race with the launch of the Explorer-1 satellite four months later.