Vocation : Science : Astronomy

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.

Prof Giorgio Abetti HFRSE (5 October 1882 – 24 August 1982) was an Italian solar astronomer.

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.

Henri Alexandre Deslandres (24 July 1853 – 15 January 1948) was a French astronomer, director of the Meudon and Paris Observatories, who carried out intensive studies on the behaviour of the atmosphere of the Sun.

Nicolas Camille Flammarion FRAS (French: [nikɔla kamij flamaʁjɔ̃]; 26 February 1842 – 3 June 1925) was a French astronomer and author. He was a prolific author of more than fifty titles, including popular science works about astronomy, several notable early science fiction novels, and works on psychical research and related topics. He also published the magazine L'Astronomie, starting in 1882. He maintained a private observatory at Juvisy-sur-Orge, France.

Pierre Jules César Janssen (22 February 1824 – 23 December 1907), usually known as Jules Janssen, was a French astronomer who, along with English scientist Joseph Norman Lockyer, is credited with discovering the gaseous nature of the solar chromosphere, and with some justification the element helium.

Johann Elert Bode (German: [ˈboːdə]; 19 January 1747 – 23 November 1826) was a German astronomer known for his reformulation and popularisation of the Titius–Bode law. Bode determined the orbit of Uranus and suggested the planet's name.

Heinrich Rantzau or Ranzow (Ranzovius) (11 March 1526 – 31 December 1598) was a German humanist writer and statesman, a prolific astrologer and an associate of Tycho Brahe. He was son of Johan Rantzau.
He was Governor of the Danish royal share in the Duchy of Holstein, a rich man and celebrated book collector. Rantzau is perhaps best remembered as a patron of scholars. His own Tractatus astrologicus de genethliacorum thematum appeared in 1597, and went through five editions by 1615. In his own time, he was regarded as a generous supporter of artists and writers in Lübeck, many of whom he engaged to write memorials of his father. Rantzau was also a successful merchant with trading interests in the east-west trade through Husum and Lübeck.Rantzau was awarded the Danish Order of the Elephant in 1580 by King Frederick II of Denmark.
His oldest son Breide Rantzau was a councillor of the Danish realm, and a younger son, Gert Rantzau, was Captain of the castles of Kronborg and Flensburg.He was the great-uncle of Josias von Rantzau, Marshal of France.