On what date did Sputnik 1 become the first artificial satellite?

Sputnik 1 became the first artificial satellite on October 4, 1957.

The Soviet Union launched Sputnik 1 from Baikonur at the start of the Space Age. The polished satellite transmitted a regular radio signal that could be detected by receivers around the world, making its presence immediately evident.

Sputnik 1 orbited Earth about every 96 minutes. Its success demonstrated that a rocket could place an object into orbit and that a satellite could operate above the atmosphere. The satellite eventually reentered the atmosphere on January 4, 1958.

Sputnik 1 is sometimes confused with Sputnik 2, which launched the dog Laika on November 3, 1957. Sputnik 1 carried instruments and a transmitter but no living passenger. Its launch intensified the United States–Soviet space competition.