Cih is the hot blue star at the centre of the W of Cassiopeia, the prototype of a class of spinning stars that throw off discs of gas and flare unpredictably.
At a glance
| type | blue-white star (class B) |
|---|---|
| distance from the Sun | 549 light-years (168 pc) |
| its light left it | 549 years ago |
| luminosity | 54,000 × the Sun |
| radius | 8.6 × the Sun |
| surface temperature | 30,000 K |
| constellation | Cassiopeia (Seated Queen) |
Read off the piece’s own catalogue, the same values it draws with.
About Cih
Cih is a hot, massive star spinning so fast that its equator nearly flings matter away. Gas leaves the star and settles into a flat disc around it, which adds bright emission lines to its spectrum and makes its brightness wander without a regular rhythm. It has been seen to brighten and fade markedly within living memory, at times becoming the brightest star of the W.
It is the prototype of the Gamma Cassiopeiae stars, and it gives off hard X-rays that are still not fully explained. Its traditional name comes from Chinese astronomy, where the star belongs to a figure representing a whip. Astronauts know it as Navi, a nickname used for navigation in the early American space programme, made from an astronaut’s middle name spelled backwards.
What you see in the piece
At the centre of the W, Cih stands out in the piece as the bluest of the five stars. It also lies farther away than Caph and Schedar, so the W loses its middle as soon as you leave the Earth’s viewpoint.
Measured or modelled
Where the hard X-rays come from is debated: the interaction of the star with its disc, or a compact companion such as a white dwarf, are both proposed.
Questions
Why is Gamma Cassiopeiae variable?
Cih spins very fast and sheds gas into a disc around itself; as the disc builds and disperses, the star brightens and fades irregularly.
How far away is Cih?
Cih is 549 light-years (168 pc) from the Sun.