Jan Oort is the founder of the Oort cloud. Jan was born April 28, 1900, and then passed away on November 5, 1992. He was big in the 20th Century for understanding the Milky Way Galaxy nature. He studies at the University of Groningen. After the University of Groningen, he was appointed astronomer to the Leiden Observatory in 1924. He worked his way up to professor at the University of Leiden and vice-director of the observatory. world war 2 he left everything for a protest for the Jewish professors in the university in 1942 he spent the war on the countryside. 1945 is when the war ended and came back to the university and became the director of the observatory where he remained till 1970. He came up with a new method of mapping the spiral structure of the galaxy using 21-cm radio waves that used hydrogen. 21-centimeter radiation, electromagnetic radiation of radio wavelength emitted by cold, neutral, interstellar hydrogen atoms. He believed that comets that had a long period came from a vast cloud of small objects which become known as the Oort cloud.
