Imre Gyula Izsák (Zalaegerszeg, Hungary, February 21, 1929 – Paris, France, April 21, 1965) was a Hungarian mathematician, physicist, astronomer, and celestial mechanician.
After his mother's early death, he continued his studies at the Lower Real School in Kőszeg, where he was particularly influenced by his geography and science teacher, Szilárd Zerinváry, who later gained national fame with his writings on astronomy and the stars.
Because of his outstanding mathematical abilities, Izsák was sent on to study at the Artúr Görgey Military Cadet Engineering School in Esztergom.
He earned his college degree in mathematics and physics at the Loránd Eötvös University of Arts and Sciences in Budapest.
After defending his doctorate and ignoring the prevailing wisdom that celestial mechanics was a resolved field, he returned to his favorite topic and started working on the trajectories of rockets and satellites.
The ultimate goal of his computations was the determination of the precise shape of the Earth, which had long been known to be approximately an ellipsoid of revolution.
He used harmonic approximation in his computations, i.e. he reconstructed the Earth's gravitational field from monopoles, dipoles, quadrupoles, etc.
He continued to work hard, agreeing to write a college textbook on the motions of satellites while lecturing at Harvard University.
Izsák was married on June 7, 1962, to Emily Kuempel Brady, a teacher of English literature at Boston University.
In 1965, he traveled to a conference on satellite-geodesics in Paris, where he died of a heart attack in his hotel room on April 21, 1965, at the age of 36.