A mixed-methods study exploring the undergraduate planetarium learning environment was conducted during the 2019--2020 academic year at a western American university. Survey responses from university faculty, observational data using the Classroom Observation Protocol for Undergraduate STEM (COPUS), and faculty interview responses were collected and analyzed to investigate how and why collegiate undergraduates were being instructed in a planetarium environment and how this environment compared to a traditional classroom counterpart. Results suggest that planetarium use is viewed by instructors as an integrated learning experience with the classroom environment, with affective learning outcomes in the planetarium complemented by cognitive learning outcomes in the classroom. COPUS observations of planetarium instruction show broad similarity to classroom instruction; however, reductions in active-learning behavior archetypes measured in the planetarium environment suggest a trade-off between interactive learning strategies and visually immersive content presentation. Implications concerning the collegiate planetarium environment and future work are discussed.