Observational cosmology is a branch of astronomy that focuses on collecting and analyzing data from telescopes and other instruments to study the large-scale structure and evolution of the universe. This field aims to understand the fundamental properties of the universe, such as its age, size, composition, and how it has changed over time. Observational cosmologists study phenomena such as the cosmic microwave background radiation, galaxy clusters, supernovae, and the distribution of galaxies to uncover the mysteries of the universe's origins and evolution. They use advanced telescopes and data analysis techniques to gather information about the universe and test theories of cosmology.