Editing Crux (section)

===Objects beyond the Local Arm===

Crux is backlit by the multitude of stars of the Scutum-Crux Arm (more commonly called the [[Scutum-Centaurus Arm]]) of the Milky Way.  This is the main inner arm in the local radial quarter of the galaxy.  Part-obscuring this is:
* The [[Coalsack Nebula]] lies partially within Crux and partly in the neighboring constellations of [[Musca]] and [[Centaurus]].{{sfn|Ridpath|Tirion|2017|pp=134–135}} It is the most prominent [[dark nebula]] in the skies, and is easily visible to the naked eye as a prominent dark patch in the southern Milky Way. It can be found 6.5° southeast from the centre of Crux or 3° east from α Crucis. Its large area covers about 7° by 5°, and is {{convert|180|pc|ly|lk=on}} away from [[Earth]].<ref name="Franco2000">{{cite journal
|last1=Franco
|first1=G.P.A.
|year=2000
|title=Interstellar Na I D lines towards the Southern Coalsack
|journal=Monthly Notices of the Royal Astronomical Society
|volume=315
|issue=3
|pages=611–621
|bibcode=2000MNRAS.315..611F
|doi=10.1046/j.1365-8711.2000.03434.x|doi-access=free
}}</ref>

A key feature of the Scutum-Crux Arm is:
* The [[Jewel Box (star cluster)|Jewel Box]], κ Crucis Cluster or NGC 4755, is a small but bright [[open cluster]] that appears as a fuzzy star to the naked eye and is very close to the easternmost boundary of Crux: about 1° southeast of Beta Crucis. The combined or total magnitude is 4.2 and it lies at a distance of {{convert|1.95|kpc|ly|lk=on}} from Earth.{{sfn|Ridpath|Tirion|2017|pp=134–135}} The cluster was given its name by [[John Herschel]],{{sfn|Ridpath|Tirion|2017|pp=134–135}} based on the range of colours visible throughout the star cluster in his telescope. About seven million years old,<ref name="webda">{{cite web
|title=WEBDA Open cluster
|work=Results for NGC 4755
|url=http://www.univie.ac.at/webda/cgi-bin/ocl_page.cgi?dirname=ngc4755
|access-date=30 April 2019}}</ref> it is one of the youngest open clusters in the Milky Way, and it appears to have the shape of a letter 'A'. The Jewel Box Cluster is classified as Shapley class 'g' and Trumpler class 'I 3 r -' cluster; it is a very rich, centrally-concentrated cluster detached from the surrounding star field. It has more than 100 stars that range significantly in brightness.{{sfn|Levy|2005|p=87}} The brightest cluster stars are mostly [[blue supergiant]]s, though the cluster contains at least one [[red supergiant]]. [[Kappa Crucis (star)|Kappa Crucis]] is a true member of the cluster that bears its name, and is one of the brighter stars at magnitude 5.9.{{sfn|Ridpath|Tirion|2017|pp=134–135}}