Presidents of the International Astronomical Union

Catherine Jeanne Cesarsky (born Catherine Jeanne Gattegno on 24 February 1943) is an Argentine and French astronomer, known for her research activities in astrophysics and for her leadership in astronomy and atomic energy. She is the current chairperson of the Square Kilometre Array's governing body, SKAO Council. She was the first female president of the International Astronomical Union (2006-2009) and the first female director general of the European Southern Observatory (1999-2007).

Édouard Benjamin Baillaud (14 February 1848 – 8 July 1934) was a French astronomer.

Robert Paul Kraft (June 16, 1927 – May 26, 2015) was an American astronomer. He performed pioneering work on Cepheid variables, stellar rotation, novae, and the chemical evolution of the Milky Way. His name is also associated with the Kraft break: the abrupt change in the average rotation rate of main sequence stars around spectral type F8.

André-Louis Danjon (French: [ɑ̃dʁelwi dɑ̃ʒɔ̃]; 6 April 1890 – 21 April 1967) was a French astronomer born in Caen to Louis Dominique Danjon and Marie Justine Binet.Danjon devised a method to measure "earthshine" on the Moon using a telescope in which a prism split the Moon's image into two identical side-by-side images. By adjusting a diaphragm to dim one of the images until the sunlit portion had the same apparent brightness as the earthlit portion on the unadjusted image, he could quantify the diaphragm adjustment, and thus had a real measurement for the brightness of earthshine. He recorded the measurements using his method (now known as the Danjon scale, on which zero equates to a barely visible Moon) from 1925 until the 1950s.
Among his notable contributions to astronomy was the design of the impersonal (prismatic) astrolabe based on an earlier prismatic astrolabe developed by François Auguste Claude which is now known as the Danjon astrolabe, which led to an improvement in the accuracy of fundamental optical astrometry. An account of this instrument, and of the results of some early years of its operation, are given in Danjon's 1958 George Darwin Lecture to the Royal Astronomical Society.He also developed the "Danjon limit", a proposed measure of the minimum angular separation between the Sun and the Moon at which a lunar crescent is visible. However, this limit may not exist.
He was Director of the Observatory of Strasbourg from 1930 to 1945 and of the Paris Observatory from 1945 to 1963.Danjon was the President of the Société astronomique de France (SAF), the French astronomical society, during two periods: 1947–49 and 1962–64.He was awarded the Prix Jules Janssen of the Société astronomique de France in 1950, and the Gold Medal of the Royal Astronomical Society in 1958.
Danjon died in 1967 in Suresnes, Hauts-de-Seine.

Ernest Benjamin Esclangon (17 March 1876 – 28 January 1954) was a French astronomer and mathematician.
Born in Mison, Alpes-de-Haute-Provence, in 1895 he started to study mathematics at the École Normale Supérieure, graduating in 1898. Looking for some means of financial support while he completed his doctorate on quasi-periodic functions, he took a post at the Bordeaux Observatory, teaching some mathematics at the university.
During World War I, he worked on ballistics and developed a novel method for precisely locating enemy artillery. When a gun is fired, it initiates a spherical shock wave but the projectile also generates a conical wave. By using the sound of distant guns to compare the two waves, Escaglon was able to make accurate predictions of gun locations.
After the armistice in 1919, Esclangon became director of the Strasbourg Observatory and professor of astronomy at the university the following year. In 1929, he was appointed director of the Paris Observatory and of the International Time Bureau, and elected to the Bureau des Longitudes in 1932. He is perhaps best remembered for initiating in 1933 the first speaking clock service, reportedly to relieve the observatory staff from the numerous telephone calls requesting the exact time. He was elected to the Académie des Sciences in 1939.
Esclangon was the President of the Société astronomique de France (SAF), the French astronomical society, from 1933–1935. In 1935, he received the Prix Jules Janssen, the society's highest award.
Serving as director of the Paris Observatory throughout World War II and the German occupation of Paris, he retired in 1944. He died in Eyrenville, France.
The binary asteroid 1509 Esclangona is named after him.
The lunar crater Esclangon is named after him.
His doctoral students include Daniel Barbier, Édmée Chandon, Louis Couffignal, André-Louis Danjon, and Nicolas Stoyko.