1957: Sputnik launched

History.com has this for 4 October:

The then-Soviet Union inaugurated the Space Age with its launch of Sputnik (photo), the world’s first artificial satellite. The spacecraft, named Sputnik after the Russian word for “satellite”, was launched from the Tyuratam launch base in the Kazakh Republic. Sputnik had a diameter of 22 inches, weighed 184 pounds, and circled Earth once every hour and 36 minutes. Traveling at eighteen thousand miles an hour, its elliptical orbit had an apogee (the farthest point from Earth) of 584 miles and a perigee (the nearest point) of 143 miles. Visible with binoculars before sunrise or after sunset, Sputnik transmitted radio signals back to Earth strong enough to be picked up by amateur radio operators. Those in the United States with access to such equipment tuned in and listened in awe as the beeping Soviet spacecraft passed over America several times a day. In January of 1958, Sputnik’s orbit deteriorated, as expected, and the spacecraft burned up in the atmosphere.
Officially, Sputnik was launched to correspond with the International Geophysical Year, a solar period that the International Council of Scientific Unions declared would be ideal for the launching of artificial satellites to study Earth and the solar system. However, many Americans feared more sinister uses of the Soviets’ new rocket and satellite technology, which was apparently strides ahead of the American space effort. Sputnik was some ten times the size of the first planned American satellite, which was not scheduled to be launched until the next year. The US government, military, and scientific community were caught off guard by the Soviet technological achievement, and their united efforts to catch up with the Soviets heralded the beginning of the “space race”.
The first US satellite, Explorer, was launched on 31 January 1958. By then, the Soviets had already achieved another ideological victory when they launched a dog into orbit aboard Sputnik 2; it died when the satellite reentered the atmosphere. The Soviet space program went on to achieve a series of other space firsts in the late 1950s and early 1960s: first man in space, first woman, first three men, first space walk, first spacecraft to impact the moon, first to orbit the moon, first to impact Venus, and first craft to soft-land on the Moon. However, the United States took a giant leap ahead in the space race in the late 1960s with the Apollo lunar-landing program, which successfully landed two Apollo 11 astronauts on the surface of the moon in July of 1969.