|Observation data: J2000 epoch|
|Right ascension||00h 13m 01.015s|
|Declination||+72° 31′ 19.085″|
|Distance||~3,500 ly (~1.0 kpc) ly|
|Apparent magnitude (V)||10.7, 11.6|
|Apparent dimensions (V)||38″ × 35″|
|Designations||Bow-Tie Nebula, Caldwell 2|
NGC 40 (also known as the Bow-Tie Nebula and Caldwell 2) is a planetary nebula discovered by William Herschel on November 25, 1788, and is composed of hot gas around a dying star. The star has ejected its outer layer which has left behind a smaller, hot star with a temperature on the surface of about 50,000 degrees Celsius. Radiation from the star causes the shed outer layer to heat to about 10,000 degrees Celsius, and is about one light-year across. About 30,000 years from now, scientists theorize that NGC 40 will fade away, leaving only a white dwarf star approximately the size of Earth.
- Media related to NGC 40 at Wikimedia Commons
- NGC 40 on WikiSky: DSS2, SDSS, GALEX, IRAS, Hydrogen α, X-Ray, Astrophoto, Sky Map, Articles and images
- Toalá, J. A.; Ramos-Larios, G.; Guerrero, M. A.; Todt, H. (2019). "Hidden IR structures in NGC 40: Signpost of an ancient born-again event". Monthly Notices of the Royal Astronomical Society. 485 (3): 3360–3369. arXiv:1902.11219. doi:10.1093/mnras/stz624.
- Kameswara Rao, N.; Sutaria, F.; Murthy, J.; Krishna, S.; Mohan, R.; Ray, A. (2018). "Planetary nebulae with UVIT: Far ultra-violet halo around the Bow Tie nebula (NGC 40)". Astronomy & Astrophysics. 609: L1. arXiv:1711.07698. Bibcode:2018A&A...609L...1K. doi:10.1051/0004-6361/201732188. S2CID 55637703.