He studied at the Lyce Malherbe and then went to the Ecole Normale Superieure during which time he worked at the observatory of the Societe Astronomique de France.

He extended similar methods to study the albedo of Venus and Mercury which became the subject of his doctoral dissertation Recherches de photometrie astronomique (1928) at Paris University.

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.

[3] The "Danjon limit", a proposed measure of the minimum angular separation between the Sun and the Moon at which a lunar crescent is visible is named after him.

[citation needed] The Danjon effect is a name given for his observation that there is an increase in the number of "dark" total lunar eclipses during the 11 year solar sunspot maxima.

[5][6] Danjon was the President of the Société astronomique de France (SAF), the French astronomical society, during two periods: 1947–49 and 1962–64.

[7][8] 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.