He participated in 11 expeditions for the study of solar eclipses,[2] and, as an advocate and theorist that additional galaxies existed outside of the Milky Way, was involved in the 1920 Shapley–Curtis Debate concerning the size and galactic structure of the universe.

From 1902 to 1920 Curtis worked at Lick Observatory, continuing the survey of nebulae initiated by Keeler.

He headed up the Lick southern station in Chile from 1905 until 1909, when he returned to take charge of the Crossley telescope.

In 1918 he observed Messier 87 and was the first to notice the astrophysical jet which he described as a "curious straight ray ... apparently connected with the nucleus by a thin line of matter.

This device is packed in crates and resided at UCO Lick Observatory as of Aug 2011.