So in 1922, the McMaths, along with Judge Henry S. Hulbert founded the McMath–Hulbert Observatory in Lake Angelus, Michigan.

It was deeded to the University of Michigan in 1931, McMath served as the director of the McMath–Hulbert Observatory until 1961.

In 1932, McMath extended the functionality of the spectroheliograph so that it could record motion pictures of the Sun.

This machine is known as a spectroheliokinematograph; with it, he took astonishing moving pictures of solar storms, showing features on the Sun's surface that lasted from seconds to days.

In 1933, he and his father received the Franklin Institute's John Price Wetherill Medal.