|Died||21 April 1967 (aged 77)|
|Known for||Danjon scale|
|Awards||Gold Medal of the Royal Astronomical Society in 1958|
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 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.
- Hockey, Thomas (2009). 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 RAS. 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 Société astronomique de France
- Fehrenbach, C. "Un grand astronome : André Danjon." L'Astronomie, 1967, Vol. 81, pp. 323-331.
- Bibliothèque nationale de France: Danjon André
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