Shangcheng

A white star in the far northern parts of Cassiopeia, near the point where that constellation borders Camelopardalis to the east, and Cepheus to the north. Shangcheng has approximately 1.8 times the mass of the Sun, and nearly three times its diameter. As a white star, it is considerably hotter than the Sun, and emits nearly thirty times as much light. Shangcheng is some 166 light years from the Solar System, and shines with a magnitude of +4.84 as seen from Earth (making it relatively faint in sky, but still visible to the naked eye under most conditions).

Shangcheng's most notable feature is its extreme rotational velocity. The star turns on its axis at a rate of 250 kilometres per second (more than a hundred times faster than the Sun). This rapid rotation is reflected in its spectrum, in which the absorption lines, which are relatively sharp for typical stellar spectra, are made broader and more 'nebulous' by the rate of Shangcheng's rotation. This rapid rotation has the effect of flattening the star's shape, so that its equator bulges outwards due to its spin.

This star takes its name Shangcheng from Chinese usage, meaning the 'Great Imperial Minister', belonging to the right wall of the Purple Enclosure (Zǐwēi Yuán) in traditional Chinese astronomy. Together with Shaocheng (Errai, or Gamma Cephei), it was conceived as forming the northern gateway of the Enclosure (part of a complex of Mansions and Enclosures used in traditional Chinese astronomy). There is in fact some uncertainty over the intended identity of the specific star that the name Shangcheng originally described. Some sources suggest that it referred to the nearby star BK Camelopardalis, while others prefer this white star, HR 932 or HD 19275 in Cassiopeia. The IAU has officially assigned the name to the latter star.