- ACHIRD (Eta Cassiopeiae). At almost fourth magnitude (3.44) and faint to the eye, and not a part of the traditional outline of Cassiopeia, Achird is often neglected.
- Achird is also among the closer stars, its distance a mere 19.4 light years
- The proper name “Achird” seems to have been applied in recent times and has no clear meaning, one unsupported source suggesting “girdle.” Better really to know it by its Greek letter name of Eta Cas.
- Achird is a yellow-white class G hydrogen-fusing dwarf (variously G0 to G3, we adopt the latter) with a surface temperature of 5730 Kelvin, just a bit cooler than the Sun.
- What makes the star really stand out, however, is its eighth- magnitude (just barely, 7.51) companion, an orange class K (K7) dwarf. Star colors are subtle. But put two stars of even somewhat different color together, especially if there is a brightness difference, and the contrast can become quite intense. Eta Cas A (the brighter) and B thus put on a fine show through even a small telescope, the pair an easily-resolvable 11 seconds of arc apart.