王良四（α Cas /仙后座α）是仙后座的最亮星，虽然有时候策（仙后座γ）比它还亮。王良四的视星等为+2.25，俗名Schedar（也作Shedar, Shadar, Schedir或Shedir），来源于阿拉伯语صدر şadr，意为“乳房”。

王良四是一颗黄巨星（光谱型K0 IIIa），比太阳温度更低但是却更亮。王良四的角直径大约为5.62±0.06弧秒，半径大约是太阳的42.3倍。 根据依巴谷天体测量卫星的测定，王良四距太阳系的距离大约为230光年(70秒差距)。

王良四有时被分类为变星，但直到19世纪才观测到其光度变化。该星的三颗伴星也记录在华盛顿双星表中。

Alpha Cassiopeiae (α Cas, α Cassiopeiae) is a second magnitude star in the constellation Cassiopeia, with the traditional name Schedar, sometimes spelled Shedir. Though listed as the "alpha star" by Johann Bayer, α Cas's visual brightness closely rivals the beta star in the constellation (Beta Cassiopeiae, also known as Caph) and it may appear marginally brighter or dimmer, depending on which passband is used. However, recent calculations from NASA's WISE telescope confirm that α Cas is the brightest in Cassiopeia, with a apparent magnitude of 2.240. Its absolute magnitude is 18 times greater than β Cas, although it is located farther away from Earth (228 light years versus 54).