Upon his return to the United States in 1931, he taught at the University of Minnesota from 1931-1967, then served as astronomer emeritus from 1967 until his death.
Saat kembali ke AS pada tahun 1931, ia mengajar di Universitas Minnesota antara tahun 1931-1967, kemudian menjabat sebagai astronom emeritus hingga saat kematiannya.