20th-century Belgian astronomers

Georges Henri Joseph Édouard Lemaître ( lə-MET-rə; French: [ʒɔʁʒ ləmɛːtʁ] ; 17 July 1894 – 20 June 1966) was a Belgian Catholic priest, theoretical physicist, mathematician, astronomer, and professor of physics at the Catholic University of Louvain. He was the first to theorize that the recession of nearby galaxies can be explained by an expanding universe, which was observationally confirmed soon afterwards by Edwin Hubble. He first derived "Hubble's law", now called the Hubble–Lemaître law by the IAU, and published the first estimation of the Hubble constant in 1927, two years before Hubble's article. Lemaître also proposed the "Big Bang theory" of the origin of the universe, calling it the "hypothesis of the primeval atom", and later calling it "the beginning of the world".

Constantin Marie Le Paige (9 March 1852 – 26 January 1929) was a Belgian mathematician.
Born in Liège, Belgium, Le Paige began studying mathematics in 1869 at the University of Liège. After studying analysis under Professor Eugène Charles Catalan, Le Paige became a professor at the Université de Liège in 1882.
While interested in astronomy and the history of mathematics, Le Paige mainly worked on the theory of algebraic form, especially algebraic curves and surfaces and more particularly for his work on the construction of cubic surfaces. Le Paige remained at the university until his retirement in 1922.

Louis Zimmer (8 September 1888 – 12 December 1970) was an astronomer and clockmaker to the King of Belgium. Most notably in 1930 he built the Jubilee (or Centenary) Clock, which is displayed on the front of the Zimmer tower. The Zimmer tower (Dutch: Zimmertoren) is a tower in Lier, Belgium, also known as the Cornelius tower, that was originally a keep of Lier's fourteenth-century city fortifications. In the museum near the tower in addition to many of Zimmer's other clock is the huge clock he constructed for the 1935 Brussels International Exposition. This is the clock was sent to the United States for the 1939 New York World's Fair. In June 1970 he was proclaimed Honorary Citizen of Lier. The asteroid Zimmer (№ 3064)(1984 BB1), was named after him in 1984.