Pluto's discovery begins a new classification story

The 100-inch telescope recorded faint points in Andromeda that could be compared across nights.

The photographic plate later helped establish that Andromeda lies outside the Milky Way; this conclusion was later, not on the exposure date.

Clyde Tombaugh found a moving point in the photographic plates he had been comparing.

By comparing images of the same star field, Tombaugh detected the movement of the object later named Pluto.

The discovery itself took place on 18 February; public announcement and naming came later.

The Soviet Union launched the first artificial Earth satellite from a spaceport in the Kazakh Soviet Republic.

Sputnik 1 began transmitting radio beeps as it orbited Earth, opening new possibilities for tracking a satellite.

Radio signals from Sputnik could be received outside the launch program, making the orbit publicly observable.

The successful launch created a new platform for studying Earth and, later, the wider universe.

The spacecraft became the first successful interplanetary probe to visit another planet.