Schwarzschild, Karl (1873–1916)

German astronomer and theoreticical physicist. He was the first to substitute a photographic plate at the telescope in place of the eye and then measure densities with a photometer. He designed and constructed some of his own instruments.

He published the first reliable results in photographic photometry, and also made outstanding contributions to celestial mechanics, stellar dynamics, optical theory, and the theory of radiative equilibrium.

Schwarzschild was born in Frankfur-am-Main and studied at Strasbourg and Munich. After his PhD 1896 he joined the Kuffner Observatory in Vienna. In 1902 he was appointed professor at Göttingen and director of the observatory. From 1909 he was director of the Astrophysical Observatory at Potsdam. He joined the army 1914, and fought in Belgium and Russia. He was the father of Martin Schwarzschild.

In 1900 he suggested that the geometry of space was possibly not in conformity with Euclidean principles. (This was 16 years before the publication of Albert Einstein's general theory of relativity.) He later gave the first exact solution of Einstein's field equations.

Schwarzschild introduced the concept of radiative equilibrium in astrophysics and was probably the first to see how radiative processes were important in conveying heat in stellar atmospheres. In 1906 he published work on the transfer of energy at and near the surface of the Sun.

He devised a multi-slit interferometer and used it to measure the separation of close double stars. During a total solar eclipse 1905, he obtained spectrograms that gave information on the chemical composition of regions at various heights on the Sun. He later designed a spectrographic objective that provided a quick, reliable way to determine the radial velocities of stars.