Ralph Hamilton Curtiss (8 February 1880 – 25 December 1929) was an American astronomer and a professor of astrophysics at the University of Michigan.
He studied the Cepheid variable W Sagittarii and examined techniques to determine radial velocity from spectrometric data.
His thesis was "Proposed Method for the Measurement and Reduction of Spectrograms for the Determination of the RadiaI Velocities of Celestial Objects.
He joined the Allegheny Observatory in 1905, working with Frank Schlesinger and moved to the University of Michigan in 1907 where he became assistant professor of astrophysics.
In 1918 he became a full professor and in 1927 he succeeded William Hussey, upon his death, as director of the Observatory of the University of Michigan.