Eta Cassiopeiae
binary star system in the constellation Cassiopeia
Eta Cassiopeiae is a binary star system in the northern constellation of Cassiopeia. Its name is a Bayer designation that is Latinized from η Cassiopeiae and abbreviated Eta Cas or η Cas. The binary nature of this system was first discovered by William Herschel in August 1779. Based upon parallax measurements, the distance to this system is 19.32 light-years (5.92 parsecs). The two components are designated Eta Cassiopeiae A (officially named Achird ) and B.
Nomenclature
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 star systems, and adopted by the International Astronomical Union (IAU).
The proper name Achird was apparently first applied to Eta Cassiopeiae in the Skalnate Pleso Atlas of the Heavens published in 1950, but is not known prior to that. Richard Hinckley Allen gives no historical names for the star in his book Star Names: Their Lore and Meaning. In 2016, the IAU organized a Working Group on Star Names (WGSN) to catalog and standardize proper names for stars. The WGSN decided to attribute proper names to individual stars rather than entire multiple systems.
“Eta Cassiopeiae” enters the record as binary star system in the constellation Cassiopeia. Crown Archives preserves that source wording while asking what Cassiopeiae, binary and star can confirm, complicate or overturn.
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“Eta Cassiopeiae” is worth following because a concise public description often conceals a longer documentary argument. Here, Cassiopeiae, binary and star provides the most credible route into that argument.
The citation trail is more important than the brevity of the summary: it shows where individual claims can be examined in context. The source revision retrieved here is dated Sep 14, 2026. The linked authority identifier is Q131757844. None of the 0 selected statements returned an explicit reference. The first chronological checks are 1779, 1950 and 2016.
The absence of detail may reflect summary conventions rather than a lack of surviving documentation. The lead is largely declarative, so disagreement and counter-evidence require a deliberate search beyond the opening account. Authority statements aid reconciliation but still require their own references, qualifiers and ranks to be checked.
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This entry incorporates text from “Eta Cassiopeiae” on English Wikipedia. Contributors are listed in the page history. Text is available under the Creative Commons Attribution-ShareAlike 4.0 License. Selected authority identifiers and statements are retrieved from Wikidata under CC0; their references and qualifiers remain part of the verification path.