Theta Cancri
Theta Cancri, Latinised from θ Cancri, is a multiple star system in the zodiac constellation of Cancer. It is visible to the naked eye as a dim point of light with an apparent visual magnitude of +5.32. The system is located at a distance of approximately 450 light-years away from the Sun, based on parallax, and is drifting further away with a radial velocity of +44 km/s. Since it is near the ecliptic, it can be occulted by the Moon and, very rarely, by planets.
| Observation data Epoch J2000.0 Equinox J2000.0 (ICRS) | |
|---|---|
| Constellation | Cancer |
| Right ascension | 08h 31m 35.73082s |
| Declination | +18° 05′ 39.9166″ |
| Apparent magnitude (V) | +5.323 |
| Characteristics | |
| Spectral type | K5 III |
| U−B color index | +1.949 |
| B−V color index | +1.565 |
| Astrometry | |
| Radial velocity (Rv) | +44.47±0.19 km/s |
| Proper motion (μ) | RA: −60.438 mas/yr Dec.: −57.331 mas/yr |
| Parallax (π) | 7.3204 ± 0.1826 mas |
| Distance | 450 ± 10 ly (137 ± 3 pc) |
| Absolute magnitude (MV) | −0.19 |
| Details | |
| Radius | 40.02+2.22 −2.35 R☉ |
| Luminosity | 353.1±10.1 L☉ |
| Temperature | 3,955+121 −105 K |
| Other designations | |
| Database references | |
| SIMBAD | data |
The primary, designated component A, is K-type giant star with a stellar classification of K5 III, having exhausted the supply of hydrogen at its core, then cooled and expanded. At present it has 40 times the girth of the Sun. It is radiating 353 times the luminosity of the Sun at an effective temperature of 3,955 K.
In Chinese astronomy, Ghost (Chinese: 鬼宿; pinyin: Guǐ Xiù) refers to an asterism consisting of Theta Cancri, Eta Cancri, Gamma Cancri and Delta Cancri. Theta Cancri is the first star of Ghost (Chinese: 鬼宿一; pinyin: Guǐ Xiù yī), as it is also the determinative star for that asterism.