Albert Einstein was a German-born theoretical physicist. Einstein developed the theory of relativity, one of the two pillars of modern physics (alongside quantum mechanics). Einstein's work is also known for its influence on the philosophy...

Alexander Alexandrovich Friedman or Friedmann was a Russian and Soviet cosmologist and mathematician. He discovered the expanding-universe solution to the general relativity field equations in 1922, which was corroborated by Edwin Hubble's...

Edwin Powell Hubble was an American astronomer who played a crucial role in establishing the field of extragalactic astronomy and is generally regarded as one of the most important observational cosmologists of the 20th century. Hubble is k...

Georges Lemaître was a Belgian Roman Catholic priest, honorary prelate, professor of physics and astronomer at the Catholic University of Leuven. He sometimes used the title Abbé or Monseigneur. Lemaître proposed what became known as the Bi...

Fritz Zwicky was a Swiss astronomer. He worked most of his life at the California Institute of Technology in the United States of America, where he made many important contributions in theoretical and observational astronomy. In 1933, Zwick...

Jan Hendrik Oort was a Dutch astronomer who made significant contributions to the understanding of the Milky Way and who was a pioneer in the field of radio astronomy. His New York Times obituary called him “one of the century's foremost ex...

Kuiper is considered to be the father of modern planetary science for his wide ranging studies of the solar system. Although he contributed to astrophysics, established the atmosphere of Saturn's moon Titan, and discovered Saturn's moon Mir...

Clyde William Tombaugh was an American astronomer. Although he is best known for discovering the dwarf planet Pluto in 1930, the first object to be discovered in what would later be identified as the Kuiper belt, Tombaugh also discovered ma...