Babcock invented and built several astronomical instruments and was the first to propose
adaptive optics in 1953. He specialized in
spectroscopy and the study of
magnetic fields of stars. He proposed the
Babcock Model, a theory for the magnetism of
sunspots. During
World War II, he was engaged in
radiation work at
MIT and
Caltech. After the war, he began a productive collaboration with his father. His undergraduate studies were at
Caltech, and his doctorate was from the
University of California, Berkeley. Babcock's 1938 doctoral thesis contained one of the earliest discoveries of
dark matter. He reported measurements of the rotation curve for the Andromeda galaxy (M31) and wrote, "The velocities therefore indicate a greater mass than that derived from the luminosity. This discrepancy can hardly be explained unless we postulate either a change in the nature of the stellar population in the outer parts of the nebula or a departure from the laws of circular motion," and "the mass-to-light ratio increases markedly at large radii. It is evident that the outer parts of the nebula contain either a great amount of non-luminous matter or that the motions depart significantly from circularity." Babcock considered the possibility that there was more dust in the outer parts of the galaxy than previously thought, thereby increasing the mass-to-light ratio, but did not conclude this was the explanation. Nonetheless, it was not until the work of Morton (Mort) Roberts in the late 1960s, Rubin & Ford, and Freeman in regard to
NGC 300, that attention to spiral galaxy rotation curves was again in the spotlight as an indication of a mass or gravity problem in spiral galaxies. Babcock was director of the
Palomar Observatory for
Caltech from 1964 to 1978. ==Honors==