Johannes Franz Hartmann was born on January, 11th, 1865 in Erfurt, Germany. His parents were Daniel Hartmann and his wife Sophia, nee Evers.
Hartmann studied in Tuebingen, Berlin and Leipzig. He presented his doctoral thesis in Leipzig in 1891 on the Earth's shadow during moon eclipses (Die Vergroesserung des Erdschattens bei Mondfinsternissen). He worked in Wien, Austria, with de Ball and again in Leipzig with Bruns. 1896 Hartmann moved to Potsdam were he worked with H.C. Vogel and was promoted to 'Observer' in 1898 and to 'Professor' in 1902. During these years he became one of the leading astrophysicists of his time. His main work was on defining standards for wavelengths as well as in instrumentation (microphotometer). During this time the big refractor with a diameter of 80 cm was installed and Hartmann found the photographic telescope to be useless: the lenses were not good enough. Then he developed a method of testing telescope lenses, which is today named after him. After refiguring the main lens according to his recommendations the telescope was in good condition and went to work. Hartmann found clouds of Calcium with this instrument during his spectrographic work. 1907 Hartmann was married in Berlin-Wilmersdorf to Angelika Scherr, born 1881. 1909 he went to Goettingen as Director of the Observatory and Professor at the University there. Since the observing conditions in Goettingen were not to his needs he went to La Plata in 1921, where he developed a theory on Novae and discovered that the minor planet Eros is not a spherical body.
In 1934 Hartmann got very ill and went back to Goettingen. There he died on September, 13th 1936. He had two sons and one daughter.
References: 1. LABITZKE, P., in: Neue Deutsche Biografie, Vol. 7, p. 744-45