Sputnik 1 was launched by the Soviet Union on 4 October 1957 and became the first artificial satellite to orbit Earth. Its radio transmitter sent out a simple beep-beep signal that amateur radio operators around the world could pick up, turning a technical transmission into a public event. The sound became a symbol of the start of the Space Race and the Cold War competition in space. Decades later it remains instantly recognisable in documentaries, classrooms and online edits about space history.