NGC 2438
Template:Short description Template:Infobox nebula
NGC 2438 is a planetary nebula in the southern constellation of Puppis.<ref name=APOD>Template:Cite APOD</ref> Parallax measurements by Gaia put the central star at a distance of roughly 1,370 light years.<ref name=GaiaDR2/> It was discovered by William Herschel on March 19, 1786.<ref name="ATLAS"/> NGC 2438 appears to lie within the cluster M46, but it is most likely unrelated since it does not share the cluster's radial velocity.<ref name=majaess2007>Template:Cite journal</ref><ref name=kiss2008>Template:Cite journal</ref>
The object is a multi-shell planetary nebula with a bright inner nebula with a diameter of Template:Val, consisting of two somewhat detached shells.<ref name="Öttl2014" /> It is expanding with a velocity of Template:Val.<ref name="Corradi2000" /> The structure is surrounded by a fainter, mostly circular halo that is more visible on the western half,<ref name="Öttl2014" /> and has a diameter of Template:Val.<ref name="Corradi2000" /> The mass of the main nebula is estimated at Template:Val, while the shell has 0.5–Template:Val.<ref name="Öttl2014" /> The main nebula has a temperature of about 10–13,000 K, rising to 15–17,000 K at the inner edge.<ref name="Dalnodar2012" />
The nebula consists of material ejected from the central star during the asymptotic giant branch stage, beginning about 8,500 years ago. The main nebula was formed at about half that age.<ref name="Corradi2000" /> The central star of this planetary nebula is a 17.7-magnitude white dwarf,<ref name="ATLAS" /> with a surface temperature of about Template:Convert.<ref name="kopernik" />