We present the analysis of the planetarium usage survey (PLUS), a two-part, mixed-methods initial study investigating planetarium use in the U.S. by undergraduate learners. Seventy-seven planetariums situated on college or university campuses within the U.S. completed an online survey during the fall of 2018 with 11 of those participating in online or phone interviews during the summer of 2019. Planetarium representatives described how their facilities were being used, types of subject materials that were being taught, what content styles are used, and how often learners are attending lessons in the planetarium. Results suggest that undergraduate learners in a planetarium environment are primarily novice, non-STEM (science, technology, engineering, and mathematics) majoring students, learning principally astronomy content, receiving instruction from a live presenter approximately once per month within a given course, for the purpose of receiving visualization-based scaffolding. Audience response systems like iClickers do not appear to be in widespread use in collegiate planetariums, and presented subject matter shows greater variety in planetariums with digital projector capacity as opposed to those with only analog projectors. Refinements to PLUS and future research plans are described.