André-Louis Danjon (April 6, 1890 – April 21, 1967) was a French astronomer born in Caen, France. April 6 is the 96th day of the year in the Gregorian calendar (97th in leap years). ... 1890 was a common year starting on Wednesday (see link for calendar). ... April 21 is the 111th day of the year in the Gregorian calendar (112th in leap years). ... 1967 was a common year starting on Sunday (the link is to a full 1967 calendar). ... An astronomer or astrophysicist is a scientist whose area of research is astronomy or astrophysics. ... Location within France Caen is a city and a commune of northwestern France. ...

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. Leonardo da Vincis sketch of crescent Moon with earthshine as part of his Codex Leicester, written between 1506 and 1510. ... Crust composition Oxygen 43% Silicon 21% Aluminium 10% Calcium 9% Iron 9% Magnesium 5% Titanium 2% Nickel 0. ... 50 cm refracting telescope at Nice Observatory. ... Prism splitting light In optics, a prism is a device used to refract light, reflect it or break it up (to disperse it) into its constituent spectral colors (colors of the rainbow), traditionally built in the shape of a right prism with triangular base. ... A diaphragm is some sort of separating membrane. ... The Danjon Scale of lunar eclipse brightness is a five-point scale useful for measuring the appearance and luminosity of the Moon during a lunar eclipse. ... 1925 was a common year starting on Thursday (link will take you to calendar). ... 1950 was a common year starting on Sunday (link will take you to calendar). ...

He won the Gold Medal of the Royal Astronomical Society in 1958. The Gold Medal is the highest award of the Royal Astronomical Society. ... 1958 was a common year starting on Wednesday (link will take you to calendar). ...

Danjon died in 1967 in Paris, France. 1967 was a common year starting on Sunday (the link is to a full 1967 calendar). ... The Eiffel Tower has become the symbol of Paris throughout the world. ...