Virtual reality (VR) technologies have the potential to transform astronomy education practices profoundly: new forms of visual representations, perceptual engagement and embodied participation promise authentic learning experiences in formal and informal learning spaces. While a growing body of research studies the educational needs and opportunities of VR astronomy education from the learner's perspective, relatively few studies have explored the perspectives of education and public outreach (EPO) professionals. This study aims to turn our attention to these complementary perspectives and shed light on design considerations for using VR in astronomy education. We unpack design principles as a dialogue between researchers and practitioners, framing this dialogue as an act of reflective practice. The findings and the ensuing dialogue draw on data from two focus group interviews with EPO professionals and scientists from the Australian Research Council Centre of Excellence for Gravitational Wave Discovery. Our design principles centre on aspects of immersion, visualisation, facilitation, and collaboration and can guide astronomy educators who wish to use VR in formal and informal learning environments. Besides, our study contributes to a deeper understanding of the new learning contexts VR technologies can create in astronomy education.