In the late 1930s he built an observatory for solar research at Climax, CO, using a telescope that mimicked a total eclipse of the sun, allowing him and his colleagues to study the solar corona and to film the spouting flames, called prominences, emitted by the Sun. Menzel initially performed solar research, but later concentrated on studying gaseous nebulae. His work with Lawrence Aller and James Gilbert Baker defined many of the fundamental principles of the study of planetary nebulae. He wrote the first edition (1964) of "A Field Guide to the Stars and Planets", part of the Peterson Field Guides. In one of his last papers, Menzel concluded, based on his analysis of the Schwarzschild equations, that black holes do not exist, and he declared them to be a myth.