Julius Johann Phillipp Ludwig Elster (December 24, 1854 in Blankenburg - April 6, 1920) was a teacher and physicist.
Of the family of the Forstmeisters, Geitel had moved in 1861 to Blankenburg. Elster and Geitel grew up in the neighborhood and attended school and high school together. The personal friendship deepened by the same interest in the natural sciences during the study years in Heidelberg and Berlin. After in Brunswick completed teaching certification went their separate ways for a short time. In 1881 they were active together at the Great School in Wolfenbüttel and used their leisure for experimental research. There had also Karl Bergwitz (1875–1958) as their students. He was awarded a honorary doctorate (1915) along with Geitel at the Technical University of Braunschweig. In 1919, Julius Elster was diagnosed with a disease (diabetes mellitus). In April 1920, the Privy Councilor Julius Elster died in Bad Harzburg during a spa stay.
Together with his friend Hans Geitel, he has well over 100 publications on atmospheric electricity, the intensity of the starlight, ihe problems of ionizing radiation (example: "On the radioactivity of the earth substrate and its possible relationship to the geothermal") and other important areas of research a valuable contribution paid to the development of physics. So Julius Elster 1893 with Geitel invented a modern photoelectric cell, the photocell.
- Rudolf GA Fricke J. Elster & H. Geitel. Childhood friends, high school teachers, scientists from passion. Döring pressure, Braunschweig, 1992, ISBN 3-925268-12-X .
- Rudolf E. Ottmer: Elster, Julius. In: New German Biography (NDB). Volume 4, Duncker & Humblot, Berlin, 1959, ISBN 3-428-00185-0, pp. 468 f (digitized).