The first man-made satellite was Sputnik 1. Launched by the Soviet Union on October 4, 1957, Sputnik 1 marked a significant milestone in the Space Age and initiated the space race between the United States and the Soviet Union. The satellite was a metal sphere, about 58 centimeters in diameter, and transmitted radio signals back to Earth, which could be received by amateur radio operators and scientists alike. Its successful launch demonstrated the feasibility of satellite technology and inspired further advancements in space exploration, leading to the eventual development of more complex satellites and long-term space missions.