André-Louis Danjon (French:[ɑ̃dʁelwidɑ̃ʒɔ̃]; 6 April 1890 – 21 April 1967) was a French astronomer born in Caen to Louis Dominique Danjon and Marie Justine Binet.[1]
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.[2]
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.
^Hockey, Thomas (2009). Hockey, Thomas; Trimble, Virginia; Williams, Thomas R.; Bracher, Katherine; Jarrell, Richard A.; Marché, Jordan D.; Ragep, F. Jamil; Palmeri, Joann; Bolt, Marvin (eds.). The Biographical Encyclopedia of Astronomers. Springer Publishing. doi:10.1007/978-0-387-30400-7. ISBN978-0-387-31022-0.
^"George Darwin Lecture". Monthly Notices of the Royal Astronomical Society. 118: 411–31. 1958.
andré, louis, danjon, french, dʁelwi, ʒɔ, april, 1890, april, 1967, french, astronomer, born, caen, louis, dominique, danjon, marie, justine, binet, born, 1890, april, 1890caendied21, april, 1967, 1967, aged, suresnesnationalityfrenchknown, fordanjon, scaleawa. Andre Louis Danjon French ɑ dʁelwi dɑ ʒɔ 6 April 1890 21 April 1967 was a French astronomer born in Caen to Louis Dominique Danjon and Marie Justine Binet 1 Andre Louis DanjonBorn 1890 04 06 6 April 1890CaenDied21 April 1967 1967 04 21 aged 77 SuresnesNationalityFrenchKnown forDanjon scaleAwardsGold Medal of the Royal Astronomical Society in 1958Scientific careerFieldsastronomyDoctoral advisorErnest Esclangon 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 Francois 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 2 Danjon Prismatic Astrolabe OPL 1954 Quito Astronomical Observatory 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 3 Danjon was the President of the Societe astronomique de France SAF the French astronomical society during two periods 1947 49 and 1962 64 4 5 He was awarded the Prix Jules Janssen of the Societe 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 6 References edit Hockey Thomas 2009 Hockey Thomas Trimble Virginia Williams Thomas R Bracher Katherine Jarrell Richard A Marche Jordan D Ragep F Jamil Palmeri Joann Bolt Marvin eds The Biographical Encyclopedia of Astronomers Springer Publishing doi 10 1007 978 0 387 30400 7 ISBN 978 0 387 31022 0 George Darwin Lecture Monthly Notices of the Royal Astronomical Society 118 411 31 1958 direction de Danjon 1945 1963 Observatoire de Paris Archived from the original on 2011 09 27 List of presidents of the Societe astronomique de France Fehrenbach C Un grand astronome Andre Danjon L Astronomie 1967 Vol 81 pp 323 331 Bibliotheque nationale de France Danjon Andre nbsp nbsp nbsp This article about a French astronomer is a stub You can help Wikipedia by expanding it vte Retrieved from https en wikipedia org w index php title Andre Louis Danjon amp oldid 1220124142, wikipedia, wiki, book, books, library,
