1677: Birth of Jacques Cassini, French astronomer and son of Giovanni Cassini, who confirmed that Saturn has rings.

1815: Birth of Jean-Baptiste Liagre. A professor of topography at the Military School, he refused the position of director after Quetelet's death and other senior appointments. He served on the executive committee between Houzeau's departure and François Folie's appointment and was also a prominent member of the scientific council of the Observatory.

1930: Clyde Tombaugh discovers Pluto when studying photographs taken in January.