viewers in Tasmania, and only low if one were in Cairns. System β Cassiopeiae is a yellow-white hued giant of stellar class F2 III with a surface temperature around . More than three times the size of and 28 times brighter than the Sun, Caph has an absolute magnitude of +1.3. It was once an A-type star with about double the Sun's mass. It is now in the process of cooling and expanding to become a red giant. Its core is likely to have used up its hydrogen and is shrinking and heating, while its outer envelope of hydrogen is expanding and cooling. Stars do not spend much time in this state and are relatively uncommon. Caph's corona is unusually weak. β Cassiopeiae is a variable star of the Delta Scuti type, in fact the second brightest of such stars in the sky after Altair. It is a monoperiodic pulsator, with a brightness that ranges from magnitude +2.25 to +2.31 with a period of 2.5 hours. This type of variable includes subgiant or main sequence stars of spectral classes F5–A0, having masses between 1.5–2.5 solar masses and nearing the end of their core hydrogen fusion lifetime. Their pulsations are related to the same helium instability strip on the Hertzsprung–Russell diagram as that of classical Cepheids. Delta Scuti stars are located at the intersection of the strip with the main sequence. This star is rotating at about 92% of its critical speed, completing 1.12 rotations every day. This is giving the star an oblate spheroid shape with an equatorial bulge that is 24% larger than the polar radius. This shape is causing the polar region to have a higher temperature than the equator: the temperature difference is about 1,000 K. The axis of rotation is inclined about 20° to the line of sight from the Earth. β Cassiopeiae was once considered to be a spectroscopic binary with a faint companion in a 27-day orbit, but it is now thought to be a single star. References External links Cassiopeiae, Beta Cassiopeiae, 11 Cassiopeia (constellation) Delta Scuti variables F-type giants Caph 0021 000432 000746 BD+58 0003 0008