Jan Oort

It’s the birthday of Jan Oort, who was born in 1900 in Franeker, the Netherlands. Oort studied physics Groningen University and earned a PhD in astronomy at Yale University. Over his long career at Leiden University he made several important discoveries. Using stellar velocity data, he determined the dynamic structure of the Milky Way. He and Hendrik van de Hulst sought and detected the 21-cm hydrogen line, which they used to observe the center of our galaxy for the first time. Oort also studied comets. He proposed in 1950 that the Solar System is surrounded by a massive spherical cloud consisting of billions of comets far beyond the orbits of Neptune and Pluto. Oort had the distinction of observing Halley’s comet twice -- as a child in 1910 and as a professional astronomer in 1986.

Date in History: 28 April 1900