been reported to be a spectroscopic binary, but this has never been confirmed. Eta Cassiopeiae A has a stellar classification of G0 V, which makes it a G-type main-sequence star like the Sun. It therefore resembles what the Sun might look like were humans to observe it from Eta Cassiopeiae. The star has 97% of the mass of the Sun and 101% of the Sun's radius. It is of apparent magnitude 3.44, radiating 129% of the luminosity of the Sun from its outer envelope at an effective temperature of . It appears to be rotating at a leisurely rate, with a projected rotational velocity of . The cooler and dimmer (magnitude 7.51) Eta Cassiopeiae B is of stellar classification K7 V; a K-type main-sequence star. It has only 57% of the mass of the Sun and 66% of the Sun's radius. Smaller stars generate energy more slowly, so this component radiates only 6% of the luminosity of the Sun. Its outer atmosphere has an effective temperature of 4,036 K. Compared to the Sun, both components show only half the abundance of elements other than hydrogen and helium—what astronomers term their metallicity. A necessary condition for the existence of a planet in this system are stable zones where the object can remain in orbit for long intervals. For hypothetical planets in a circular orbit around the individual members of this star system, this maximum orbital radius is computed to be 9.5 AU for the primary and 7.1 AU for the secondary. (Note that the orbit of Mars is 1.5 AU from the Sun.) A planet orbiting outside of both stars would need to be at least 235 AU distant. See also Lists of stars List of stars in Cassiopeia References External links Cassiopeiae, Eta Binary stars Cassiopeia (constellation) G-type main-sequence stars K-type main-sequence stars Cassiopeiae, Eta Cassiopeiae, 24 003821 RS Canum Venaticorum variables 0219 004614 Durchmusterung objects Gliese and GJ objects