Which astronomer was the first person to find observational evidence for the expansion of the universe?

The expansion of the universe is recognized and conventionally defined as the increase in distance between any two given gravitationally unbound parts of the observable universe with time. In practical language, the universe does not expand “into” anything and does not require space to exist “outside” it. Technically, neither space nor objects in space move. Instead, it is the metric (which govern the size and geometry of space itself) that changes in scale.

Swedish astronomer Knut Lundmark (1889-1958) was the first person to find observational evidence for the expansion of the universe in 1924. In addition to being an astronomer, he was a professor of astronomy and head of the observatory at Lund University from 1929 to 1955. Lund University is a public research university, one of northern Europe’s oldest, located in the city of Lund in the province of Scania, Sweden.

He received his astronomical education at the observatory of Uppsala University. During the 1920s, Lundmark worked at several observatories in the USA, mainly the Lick Observatory outside San Jose, California and the Mount Wilson Observatory, located in Los Angeles County, California.

Lundmark was a pioneer in the modern study of galaxies and their distances. He studied light distribution in the galaxies and was one of the first to suspect that galaxies are remote stellar systems at vast distances, not nearby objects belonging to our own galaxy, the Milky Way.