A satellite broadcast reaches ground listeners

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 object initially joined the planetary list and was reclassified as a dwarf planet many decades afterward.

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.

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.

Mariner 2 measured properties of the planet while passing it without entering orbit.

Mariner 2 showed that interplanetary spacecraft could return measurements from distant worlds.

The flyby provided direct data to compare with Earth-based astronomical observations.