Born Paris, France, 21 January 1884
French solar astronomer Lucien d’Azambuja inaugurated an 80-year-long sequence of daily images of the solar surface and chromosphere that is a unique data resource for studies of changes in the Sun and their correlations with other phenomena. At the age of only 15, he began working as an assistant at the Observatory of Meudon, near Paris, under Henri Deslandres , earning a doctoral degree there many years later, in 1930, for his work on the structure of the chromosphere. In 1908, d’Azambuja was promoted to “astronomer,” and he built a large spectroheliograph, which had been designed by Deslandres to study chromospheric structures. The instrument allowed convenient imaging and radial velocity measurements of the different layers in the solar chromosphere. It is especially useful for the study of the solar prominences. Solar prominences – bright clouds on the Sun’s limb – were eventually proved to be identical to the dark filaments that can be seen on the Sun’s disk with the spectroheliograph each day.
After 1913, when Deslandres and d’Azambuja were convinced that filaments are one of the most important elements of the upper layer of the chromosphere, they proposed a graphic representation that would allow convenient study of individual filaments and of filaments’ global distribution. This was the first draft of a synoptic map for following the chromospheric structures during each 27-day solar rotation. Determining the velocity of rotation and the height of filaments was one of d’Azambuja’s scientific passions.
In 1927, the observatories of Paris and Meudon were unified, and Deslandres became the director, leaving the responsibility of the solar department on d’Azambuja. The principal program of the department became the daily survey of the Sun using the spectroheliograph, starting in 1919 and continuing until the present. Every day, three spectroheliograms are obtained in the red line of hydrogen at 6,563 Å; in the continuum at 6,548 Å; and in the blue line of Ca II, K at 3,933 Å. These images are used to make the synoptic charts. More than 100,000 spectroheliograms are collected at the Meudon Observatory. They provide a unique data resource for retrospective solar research and are a tribute to d’Azambuja’s dedication.
Research at Meudon was suspended during World War II, but afterward, d’Azambuja and his wife Marguerite Roumens, who had originally been his assistant at the observatory, continued their research, making the first measurement of the rotation of the Sun from the positions of long-lived filaments, rather than from sunspots. Their work, “A Comprehensive Study of Solar Prominences and Their Evolution from Spectroheliograms Obtained at the Observatory and from Synoptic Maps of the Chromosphere Published at the Observatory” (Ann. de l’Observatoire de Meudon, Vol. 6, part 7) was published in 1948. This work was a standard reference work in solar physics for many years.
D’Azambuja worked at Meudon until 1959. He published more than 80 papers. His remarkable 60-year career bridged the period from the classical work of Jules Janssen and Deslandres to the birth of solar radio astronomy and the space age.
D’Azambuja was president of the Commission on Solar Physics of the International Astronomical Union from 1932 to 1958 and of the Astronomical Society of France (1949–1951). He also presided over a joint commission of the International Council of Scientific Unions established to study solar-terrestrial relations in the 1940s, and was elected to the French Legion of Honor, among other awards.