Jan Oort was a Dutch astronomer born on April 28, 1900, and he is best known for his work in the field of astrophysics. He made significant contributions to our understanding of the Milky Way galaxy, particularly in mapping its structure and dynamics. Oort proposed the existence of a galactic halo and was instrumental in the discovery of the Oort Cloud, a region of icy bodies surrounding the solar system. Oort's research also extended to the study of comets. He formulated the Oort Cloud hypothesis, suggesting that comets originate from this distant area. His work has had a lasting impact on astronomy, influencing how scientists study celestial objects and the formation of the solar system.