55 Cancri
| Observation data Epoch J2000.0 Equinox J2000.0 | |
|---|---|
| Constellation | Cancer |
| Pronunciation | /ˈkæŋkraɪ/ or /ˈkæŋkriː/ |
| 55 Cancri A | |
| Right ascension | 08h 52m 35.8111s |
| Declination | +28° 19′ 50.955″ |
| Apparent magnitude (V) | 5.95 |
| 55 Cancri B | |
| Right ascension | 08h 52m 40.8627s |
| Declination | +28° 19′ 58.821″ |
| Apparent magnitude (V) | 13.15 |
| Characteristics | |
| 55 Cancri A | |
| Evolutionary stage | Main sequence |
| Spectral type | K0IV–V |
| U−B color index | 0.63 |
| B−V color index | 0.87 |
| 55 Cancri B | |
| Evolutionary stage | Main sequence (red dwarf) |
| Spectral type | M4.5V |
| B−V color index | 1.7 |
| Astrometry | |
| 55 Cancri A | |
| Radial velocity (Rv) | 27.51 km/s |
| Proper motion (μ) | RA: −485.681 mas/yr Dec.: −233.517 mas/yr |
| Parallax (π) | 79.4482±0.0429 mas |
| Distance | 41.05 ± 0.02 ly (12.587 ± 0.007 pc) |
| Absolute magnitude (MV) | +5.50 |
| 55 Cancri B | |
| Proper motion (μ) | RA: −481.176 mas/yr Dec.: −244.544 mas/yr |
| Parallax (π) | 79.6560±0.0475 mas |
| Distance | 40.95 ± 0.02 ly (12.554 ± 0.007 pc) |
| Absolute magnitude (MV) | +12.58±0.088 |
| Details | |
| 55 Cancri A | |
| Mass | 0.905±0.015 M☉ |
| Radius | 0.980±0.015 R☉ |
| Luminosity | 0.617±0.009 L☉ |
| Surface gravity (log g) | 4.41±0.02 cgs |
| Temperature | 5,172±18 K |
| Metallicity [Fe/H] | +0.32±0.02 dex |
| Rotation | 38.8±0.05 days |
| Rotational velocity (v sin i) | 2.30±0.64 km/s |
| Age | 8.6±1 Gyr |
| 55 Cancri B | |
| Mass | 0.264±0.007 M☉ |
| Radius | 0.268±0.009 R☉ |
| Luminosity | 0.00788±0.00013 L☉ |
| Temperature | 3,320±51 K |
| Metallicity [Fe/H] | 0.15±0.16 dex |
| Rotation | 92±5 days |
| Rotational velocity (v sin i) | 2.36 km/s |
| Other designations | |
| Copernicus, Rho1 Cancri, 55 Cnc, BD+28°1660, GJ 324, HD 75732, HIP 43587, HR 3522, SAO 80585 | |
| Database references | |
| SIMBAD | data |
| 55 Cnc B | |
| Exoplanet Archive | data |
| ARICNS | data |
55 Cancri is a binary star system located 41 light-years away from the Sun in the zodiac constellation of Cancer. It has the Bayer designation Rho1 Cancri (ρ1 Cancri); 55 Cancri is the Flamsteed designation (abbreviated 55 Cnc). The system consists of a K-type star (designated 55 Cancri A, also named Copernicus /koʊˈpɜːrnɪkəs/) and a smaller red dwarf (55 Cancri B).
As of 2025, four extrasolar planets, designated 55 Cancri Ab, Ac, Ae and Af, named Galileo, Brahe, Janssen, and Harriot, respectively, and two planet candidates 55 Cancri Ad (named Lipperhey) and 55 Cancri Ag are known to orbit 55 Cancri A; alongside two extrasolar planets, designated Bb and Bc, which are known to orbit 55 Cancri B.