Trumpler entered the Universität Zürich but later transferred to the University of Göttingen where he earned his PhD in 1910.

[1] He is most noted for observing that the brightness of the more distant open clusters was lower than expected, and the stars appeared more red.

[2] Trumpler further studied and catalogued open clusters in order to determine the size of the Milky Way galaxy.

At first he thought his analysis placed an upper limit on the Milky Way's diameter of about 10,000 parsecs with the Sun located somewhat near the center although he later revised this.

[4] The following celestial features are named after him: Trumpler's classification method for open star clusters is still currently in use by astronomers.