A blink comparator reveals a distant object

On the night of 5–6 October Hubble photographed a spiral arm of Andromeda.

Hubble initially marked three suspected novae on the image; later comparisons revealed one was variable.

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.

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.

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