| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Cancer |
| Right ascension | 08h 23m 55.20829s[1] |
| Declination | +10° 37′ 55.4169″[1] |
| Apparent magnitude (V) | 6.08[2] |
| Characteristics | |
| Spectral type | M2III[3] |
| B−V color index | 1.507±0.004[4] |
| Variable type | suspected[5] |
| Astrometry | |
| Radial velocity (Rv) | 4.53[1] km/s |
| Proper motion (μ) | RA: −0.843[1] mas/yr Dec.: −22.943[1] mas/yr |
| Parallax (π) | 4.1258 ± 0.0272 mas[1] |
| Distance | 791 ± 5 ly (242 ± 2 pc) |
| Details | |
| Radius | 53[6] R☉ |
| Luminosity | 587[6] L☉ |
| Temperature | 3,885[6] K |
| Other designations | |
| Database references | |
| SIMBAD | data |
21 Cancri is a double star in the northern zodiac constellation of Cancer. It is just visible to the naked eye as a dim, red-hued star with an apparent visual magnitude of 6.08.[2] The star is located around 791 light years away from the Sun, based on parallax. It is moving further from the Earth with a heliocentric radial velocity of 35 km/s.[6]
The brighter component is an aging red giant with a stellar classification of M2III.[3] It is currently on the asymptotic giant branch, indicating this is a highly evolved star that has exhausted both its core hydrogen and core helium.[7] This is a suspected variable star.[5] It has expanded to 53[6] times the radius of the Sun and is radiating 587[6] times the Sun's luminosity from its swollen photosphere at an effective temperature of 3,885 K.[6] A 9th magnitude companion star is located one arc second away.[7]
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