Vesto Slipher, an astronomer at the Lowell Observatory in Arizona, made a groundbreaking observation that changed our understanding of the universe. He discovered that distant galaxies were moving away from Earth, which indicated that the universe was dynamic rather than static, overturning a long-held belief among scientists. This finding was critical in shaping modern cosmology and contributed to the development of the Big Bang theory.

Slipher's work laid the foundation for further research into the universe's expansion, prompting scientists to explore the implications of a constantly changing cosmos. His initial observations opened up new avenues of inquiry, leading to a deeper understanding of the nature of galaxies and the overall structure of the universe.