TBC
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Apparently first applied to η Cassiopeiae in the Skalnate Pleso Atlas of the Heavens published in 1950, but is not known prior to that.
Eta Cassiopeiae (η Cassiopeiae, abbreviated Eta Cas, η Cas) is a binary star system in the northern circumpolar constellation of Cassiopeia. Its binary nature was first discovered by William Herschel in August 1779. Based upon parallax measurements, the distance to this system is 19.42 light-years (5.95 parsecs) from the Sun. The two components are designated Eta Cassiopeiae A (officially named Achird , the traditional name for the system) and B.
η Cassiopeiae (Latinised to Eta Cassiopeiae) is the system's Bayer designation. The designations of the two constituents as Eta Cassiopeiae A and B derive from the convention used by the Washington Multiplicity Catalog (WMC) for multiple star systems, and adopted by the International Astronomical Union (IAU).[13]
