Prof Henry Norris Russell ForMemRS HFRSE FRAS (October 25, 1877 – February 18, 1957) was an American astronomer who, along with Ejnar Hertzsprung, helped create the Hertzsprung–Russell diagram (1910). In 1923, working with Frederick Saunders, he developed Russell–Saunders coupling, which is also known as LS coupling. This concerns the way electrons interact in light atoms.