Imre Gyula Izsák (Zalaegerszeg, Hungary, February 21, 1929 – Paris, France, April 21, 1965) was a Hungarian mathematician, physicist, astronomer, and celestial mechanician.
Imre Izsák's father, Gyula Izsák taught geography and biology in Zalaegerszeg. His mother, Aranka Pálfi, was a mathematics and physics teacher. His uncle, Tibor Szele, was a professor of mathematics in Szeged.
He got his basic schooling in Zalaegerszeg. After his mother's tragic and early death, he continued his studies at the Lower Real School in Kőszeg. There, 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, he was sent on to study at the Artúr Görgey Military Cadet Engineering School in Esztergom. Near the end of the Second World War, his entire class of military cadets was taken to Germany, where he became a prisoner of war.
Upon his return to his native town from a prisoner-of-war camp in the fall of 1945, he enrolled in the 6th grade of Ferenc Deák High School (currently Miklós Zrínyi High School). The following year, he simultaneously completed 7th and 8th grade with outstanding results, while he ranked 1st and 2nd in national mathematics competitions.
He earned his college degree in mathematics and physics at the Loránd Eötvös University of Arts and Sciences in Budapest. While there, he was a resident of Eötvös College (a residential college for elite students within the Loránd Eötvös University). During his second year, he published a paper which stirred up some controversy, as some could not believe that such a paper on differential geometry was written by a young student. Attending lectures by István Földes raised his interest in celestial mechanics. Already during his college years, he was an assistant at the observatory founded by Miklós Konkoly-Thege. He continued working there after earning his degree in the summer of 1951. In the observatory, he worked under the supervision of László Detre and Júlia Balázs, and started working on his advanced degree at the young age of 22.
In 1953, he joined the Szabadsághegyi Observatory. Subsequently, he taught at the University of Arts and Sciences in Szeged.
He was interested in the three-body problem and the n-body problem. He studied the light emissions of quasars. After defending his doctorate—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. Putting his work to practice would have been possible only in the Soviet Union or the USA. However, current international connections in Hungary were unfortunately limited to the occasional conference in the Soviet Union. Therefore in November 1956, during the Hungarian revolution, he took advantage of the open borders and emigrated to Austria.
Soon thereafter, he traveled to Switzerland, where the director of the Zürich Observatory offered him a position. He arrived in Zürich on January 9, 1957. By April, he was a full-time researcher at the institute for solar physics. Besides his research, he taught celestial navigation and time measurement to college students. He started learning English and became part of the international scientific community. His results on computing satellite orbits earned him an invitation to Cincinnati, Ohio. Soon he became one of the most respected authorities on the topic. He got a new offer for a position at the Smithsonian Astrophysical Observatory in Cambridge, Massachusetts. This was the primary institute for processing the orbital data of U.S. satellites. The work he started in Cambridge in 1959 brought the greatest successes of his short life. He had access to computers, which he needed to carry out much more precise computations than previously. The pace of the work was intense. He and his collaborators published one paper after another, and extended their work to the geodesic applications of satellites too.
The ultimate goal of his computations was the determination of the precise shape of the Earth. It had long been known that the shape of the Earth was approximately an ellipsoid of revolution. He used observations of satellite orbits to compute deviations from this shape. The classic problem of celestial mechanics is to compute the orbit of a moon given a known distribution of mass. He solved the inverse problem. He used harmonic approximation in his computations, i.e. he reconstructed the Earth's gravitational field from monopoles, dipoles, quadrupoles, etc. The shape that results from such a computation may not match the shape of the Earth exactly, but has exactly the same gravitational field. He found that the shape of the equator was not exactly a circle, but deviated from that by about 400 meters. This result was magnitudes better than any previous approximation.
On June 1, 1961, he officially announced his computations of the shape of the Earth and its surface. These brought him to the center of scientific attention, and earned him international fame practically overnight. He kept receiving invitations and gave lectures all over the world. He continued to work hard; agreed to write a college textbook on the motions of satellites, while lecturing at Harvard University. As an acknowledgment his accomplishments, he became a chief scientist at NASA.
He got married on June 7, 1962. His wife, Emily Kuempel Brady taught English literature at Boston University. He became a U.S. citizen on February 24, 1964. That fall, his son named Andrew was born.
In 1965, he traveled to a conference on satellite-geodesics in Paris. One morning, he failed to show up at the conference. He died of a heart attack in his hotel room on April 21, 1965, at the age of 36. He was buried in Cambridge, MA, on April 28.