Sputnik 1 was the first artificial satellite to be put into Earth's orbit. It was launched into an elliptical low Earth orbit

Low Earth orbit

A low Earth orbit is generally defined as an orbit within the locus extending from the Earth’s surface up to an altitude of 2,000 km...

 by the Soviet Union

Soviet Union

The Soviet Union , officially the Union of Soviet Socialist Republics , was a constitutionally socialist state that existed in Eurasia between 1922 and 1991....

 on 4 October 1957. The unanticipated announcement of Sputnik 1s success precipitated the Sputnik crisis

Sputnik crisis

The Sputnik crisis is the name for the American reaction to the success of the Sputnik program. It was a key event during the Cold War that began on October 4, 1957 when the Soviet Union launched Sputnik 1, the first artificial Earth satellite....

 in the United States

United States

The United States of America is a federal constitutional republic comprising fifty states and a federal district...

 and ignited the Space Race

Space Race

The Space Race was a mid-to-late 20th century competition between the Soviet Union and the United States for supremacy in space exploration. Between 1957 and 1975, Cold War rivalry between the two nations focused on attaining firsts in space exploration, which were seen as necessary for national...

, a part of the larger Cold War

Cold War

The Cold War was the continuing state from roughly 1946 to 1991 of political conflict, military tension, proxy wars, and economic competition between the Communist World—primarily the Soviet Union and its satellite states and allies—and the powers of the Western world, primarily the United States...

. The launch ushered in new political, military, technological, and scientific developments. While the Sputnik launch was a single event, it marked the start of the Space Age

Space Age

The Space Age is a time period encompassing the activities related to the Space Race, space exploration, space technology, and the cultural developments influenced by these events. The Space Age is generally considered to have begun with Sputnik...

.

Apart from its value as a technological first, Sputnik also helped to identify the upper atmospheric layer's density, through measuring the satellite's orbital changes.