Algarni, Eman. “Distances to Planetary Nebulae Using Astrometric Data of Gaia DR2”. International Journal of Sciences: Basic and Applied Research (IJSBAR) 54, no. 4 (November 6, 2020): 80–110. Accessed April 29, 2024. https://gssrr.org/index.php/JournalOfBasicAndApplied/article/view/11904.