French physicist and astronomer. His work in spectroscopy led to his construction of the spectroheliograph for his solar studies. In 1902 he predicted that the Sun would be found to be a source of radio waves, and 40 years later this was confirmed.
Deslandres was born and educated in Paris. In 1897 he moved to the observatory at Meudon, where he became director 1907. The Paris and Meudon Observatories were combined in 1926. Deslandres retired 1929.
Deslandres's early scientific work in spectroscopy led to the formulation of two simple empirical laws describing the banding patterns in molecular spectra; the laws were later found to be easily explained using quantum mechanics.
In 1891 US astronomer George Ellery Hale and Deslandres independently constructed a photographic device for studying the solar spectrum in detail. Deslandres's spectroheliograph was finished a year later than Hale's spectrograph but was particularly well adapted to studying the solar chromosphere.