1. The Expanding Universe: Hubble observed that galaxies were moving away from each other, and the farther away they were, the faster they were receding. This led to the groundbreaking realization that the universe is expanding. This discovery, based on the redshift of light from distant galaxies, completely changed our understanding of the universe's structure and evolution. It provided strong support for the Big Bang theory.
2. Classification of Galaxies: Hubble created a system for classifying galaxies based on their shape and structure. He categorized them into elliptical, spiral, and irregular galaxies. This classification scheme, still widely used today, enabled astronomers to study the diversity of galaxies and understand their evolution.
These two discoveries cemented Hubble's place as one of the most important astronomers of the 20th century. His work laid the foundation for modern cosmology and helped us understand the vast and dynamic nature of the universe.
