Development of the Henry Draper Catalog of Stellar Classifications Was

Multiple Choice

Development of the Henry Draper Catalog of stellar classifications was begun in the late nineteenth century.The catalog originally classified stars according to the strengths of their hydrogen lines.By the 1920s,however,the sequence had been reorganized so that the stars were classified by surface temperature.What important scientific development made possible this reinterpretation?

A) the discovery of nuclear physics and how stars generate their energy
B) the discovery of blackbody radiation and the blackbody curve
C) the development of atomic physics and how atoms emit light
D) the development of radio astronomy and the detection of molecules in space