Friedrich II. Graf von Hahn (July 27, 1742 – October 9, 1805) was a German nobleman, a philosopher and astronomer. He suggested the Doppler effect before Doppler.
Von Hahn was born in Neuhaus, Holstein. In 1793 he started the construction of a private observatory, the first in Mecklenburg, which was well equipped. He owned some of the largest mirrors made by William Herschel and precision instruments for determining the position of stars. In 1800, he discovered the central star in M57, the Ring Nebula in the constellation Lyra.