9 October

1873: On 9 October 1873, Karl Schwarzschild was born.

Schwarzschild was a German theoretical astrophysicist who made both practical and theoretical contributions to 20th century astronomy.

He developed the use of photography for measuring variable stars. While on the Russian front during military service, he computed the first two exact solutions of the Einstein Field Equations of General Relativity, which led directly to modern research on black holes.