Editing Eta Carinae (section)

==Distance==
The distance to η&nbsp;Carinae has been determined by several different methods, resulting in a widely accepted value of {{Convert|2330|pc|abbr=off}}, with a margin of error around {{Convert|100|pc|abbr=off}}.<ref name="company"/> The distance to η&nbsp;Carinae itself cannot be measured using [[Stellar parallax|parallax]] due to its surrounding nebulosity, but other stars in the Trumpler 16 cluster are expected to be at a similar distance and are accessible to parallax. [[Gaia Data Release 2]] has provided the parallax for many stars considered to be members of Trumpler 16, finding that the four hottest O-class stars in the region have very similar parallaxes with a mean value of {{val|0.383|0.017|u=milliarcseconds}} (mas), which translates to a distance of {{val|2600|100|u=parsecs|fmt=commas}}. This implies that η&nbsp;Carinae may be more distant than previously thought, and also more luminous, although it is still possible that it is not at the same distance as the cluster or that the parallax measurements have large systematic errors.<ref name="davidson2018">{{cite journal|bibcode=2018RNAAS...2..133D|title=Gaia, Trumpler 16, and Eta Carinae|journal=Research Notes of the American Astronomical Society|volume=2|issue=3|pages=133|last1=Davidson|first1=Kris|last2=Helmel|first2=Greta|last3=Humphreys|first3=Roberta M.|year=2018|doi=10.3847/2515-5172/aad63c|arxiv=1808.02073|s2cid=119030757 |doi-access=free }}</ref>

The distances to star clusters can be estimated by using a [[Hertzsprung–Russell diagram]] or [[colour–colour diagram]] to calibrate the [[absolute magnitude]]s of the stars, for example fitting the [[main sequence]] or identifying features such as a [[horizontal branch]], and hence their distance from Earth. It is also necessary to know the amount of interstellar extinction to the cluster and this can be difficult in regions such as the Carina Nebula.<ref name="the">{{cite journal |bibcode=1980A&AS...41...93T|title=Studies of the Carina Nebula. IV – A new determination of the distances of the open clusters TR 14, TR 15, TR 16 and CR 228 based on Walraven photometry|journal=Astronomy and Astrophysics Supplement Series|volume=41|pages=93|last1=The|first1=P. S.|last2=Bakker|first2=R.|last3=Antalova|first3=A.|year=1980}}</ref> A distance of {{convert|7330|ly|abbr=off|pc}} has been determined from the calibration of [[O-type star]] luminosities in Trumpler 16.<ref name="content">{{cite journal |bibcode=1995RMxAC...2...51W|title=The Stellar Content of the Carina Nebula (Invited Paper)|journal=Revista Mexicana de Astronomía y Astrofísica, Serie de Conferencias |volume=2|pages=51|last1=Walborn|first1=N. R.|year=1995}}</ref> After determining an abnormal reddening correction to the extinction, the distance to both Trumpler 14 and Trumpler 16 has been measured at {{val|9500|1000|fmt=commas|u=light-years}} ({{val|2900|300|fmt=commas|u=parsecs}}).<ref name="hur">{{cite journal|doi=10.1088/0004-6256/143/2/41|title=Distance and the Initial Mass Function of Young Open Clusters in the η Carina Nebula: Tr 14 and Tr 16|journal=The Astronomical Journal|volume=143|issue=2|pages=41|year=2012|last1=Hur|first1=Hyeonoh |last2=Sung|first2=Hwankyung|last3=Bessell|first3=Michael S.|bibcode=2012AJ....143...41H|arxiv = 1201.0623|s2cid=119269671}}</ref>

The known expansion rate of the Homunculus Nebula provides an unusual geometric method for measuring its distance. Assuming that the two lobes of the nebula are symmetrical, the projection of the nebula onto the sky depends on its distance. Values of 2,300, 2,250, and {{val|2300|fmt=commas|u=parsecs}} have been derived for the Homunculus, and η&nbsp;Carinae is clearly at the same distance.<ref name="company">{{cite book|doi=10.1007/978-1-4614-2275-4_2 |chapter=The company Eta Carinae keeps: Stellar and interstellar content of the Carina Nebula |title=Eta Carinae and the Supernova Impostors|volume=384|pages=25–27|series=Astrophysics and Space Science Library|year=2012|last1=Walborn|first1=Nolan R. |isbn=978-1-4614-2274-7|bibcode=2012ASSL..384...25W}}</ref>