Otto Hermann Leopold Heckmann was a German astronomer.
He directed the Hamburg Observatory from 1941 to 1962, after which he became the first director of the European Southern Observatory. He actively contributed to the creation of the third issue of the Astronomische Gesellschaft Katalog. He also contributed to cosmology based on the fundamentals of general relativity, and wrote the book Theorien der Kosmologie.
He won the James Craig Watson Medal in 1961 and the Bruce Medal in 1964.
Heckmann also served as President of the International Astronomical Union in 1967, and following a Polish request and under the impression of German acts in Poland during World War II, made the controversial decision to hold an Extraordinary IAU General Assembly in February 1973 in Warsaw, Poland, to commemorate the 500th anniversary of Nicolaus Copernicus, shortly after the regular 1973 GA was held in Australia.
The asteroid 1650 Heckmann is named after him. He married Johanna Topfmeier in 1925 and they had three children together.