Rho Cassiopeiae
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Cassiopeia |
| Right ascension | 23h 54m 23.0s |
| Declination | +57° 29′ 58″ |
| Apparent magnitude (V) | 4.1 to 6.2 |
| Characteristics | |
| Spectral type | G2 0 (F8pIa – K0pIa-0) |
| U−B color index | 1.15 |
| B−V color index | 1.26 |
| Variable type | SRd |
| Astrometry | |
| Radial velocity (Rv) | −47 km/s |
| Proper motion (μ) | RA: −4.54 mas/yr Dec.: −3.45 mas/yr |
| Parallax (π) | 0.9470±0.2021 mas |
| Distance | 8,150±1,630 ly (2,500±500 pc) |
| Absolute magnitude (MV) | –9.5 |
| Details | |
| Mass | 40 M☉ |
| Radius | 564 or 700 R☉ (2023) 345 – 773 R☉ |
| Luminosity | 300,000 – 530,000 L☉ |
| Surface gravity (log g) | 0.1 cgs |
| Temperature | 4,500 – 8,000 K |
| Metallicity [Fe/H] | 0.3 dex |
| Rotational velocity (v sin i) | 25 km/s |
| Age | 4 – 6 Myr |
| Other designations | |
| 7 Cassiopeiae, HR 9045, BD+56°3111, HD 224014, SAO 35879, FK5 899, HIP 117863, GC 33160 | |
| Database references | |
| SIMBAD | data |
Rho Cassiopeiae (/ˌroʊ kæsiəˈpiːaɪ, -sioʊ-, -iː/; ρ Cas, ρ Cassiopeiae) is a yellow hypergiant star in the constellation Cassiopeia. It is about 8,000 light-years (2,500 pc) distant, yet can still be seen by the naked eye as it is over 300,000 times brighter than the Sun. On average it has an absolute magnitude of −9.5, making it one of the most luminous stars known in visual wavelengths. Its diameter varies between about 300 and 800 times that of the Sun, or 1.4 to 3.7 times the size of Earth's orbit.
Louisa Wells discovered that the star's brightness varies, and that discovery was published in 1901. Rho Cassiopeiae is a single star, and is categorized as a semiregular variable. As a yellow hypergiant, it is one of the rarest types of stars. Only a few dozen are known in the Milky Way, but it is not the only one in its constellation which also contains V509 Cassiopeiae.