Today in the history of astronomy, the man behind the Oort Cloud is born. | Published: April 28, 2026 Jan Oort poses in front of an image of M81. Oort studied M81 (and several other galaxies) in his research into the structure and rotation of spiral galaxies. Credit: Joop van Bilsen, CC0, via Wikimedia Commons Dutch astronomer Jan Oort , born April 28, 1900, studied physics and astronomy and went on to a long career at Leiden University. Oort was a pioneer in 20th-century astronomy, revolutionizing our understanding of galaxy rotation, radio astronomy, and dark matter. In 1950, Oort proposed the existence of a huge group of trillions of pieces of icy debris at the outer edge of our solar system. This massive collection, which we today call the Oort Cloud , begins 1,000-5,000 astronomical units from the Sun, and extends almost halfway to Alpha Centauri.…