| APA | Smart Define. (2013). extragalactic nebula thesaurus. Retrieved September 24, 2026, from https://smartdefine.org/extragalactic_nebula/thesaurus/narrower |
| Chicago | Smart Define. 2013. "extragalactic nebula thesaurus" https://smartdefine.org/extragalactic_nebula/thesaurus/narrower (accessed September 24, 2026). |
| Harvard | Smart Define 2013, extragalactic nebula thesaurus, Smart Define, viewed 24 September, 2026, <https://smartdefine.org/extragalactic_nebula/thesaurus/narrower>. |
| MLA | Smart Define. "extragalactic nebula thesaurus" 19 May 2013. Web. 24 September 2026. <https://smartdefine.org/extragalactic_nebula/thesaurus/narrower> |