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.
The name ‘bird’s foot’ refers to the appearance of the seed pods on their stalk. Five leaflets are present, but with the central three held conspicuously above the others, hence the use of the name ’trefoil’.
