Global InformationPolaris information
  | |
| Observation data Epoch J2000 Equinox | |
|---|---|
| Constellation | Ursa Minor |
| Pronunciation | /pəˈlɛərɪs, -ˈlær-/; UK: /pəˈlɑːrɪs/[1] |
| α UMi A | |
| Right ascension | 02h 31m 49.09s[2] |
| Declination | +89° 15′ 50.8″[2] |
| Apparent magnitude (V) | 1.98[3] (1.86 – 2.13)[4] |
| α UMi B | |
| Right ascension | 02h 30m 41.63s[5] |
| Declination | +89° 15′ 38.1″[5] |
| Apparent magnitude (V) | 8.7[3] |
| Characteristics | |
| α UMi A | |
| Spectral type | F7Ib[6] |
| U−B color index | 0.38[3] |
| B−V color index | 0.60[3] |
| Variable type | Classical Cepheid[4] |
| α UMi B | |
| Spectral type | F3V[3] |
| U−B color index | 0.01[7] |
| B−V color index | 0.42[7] |
| Variable type | suspected[4] |
| Astrometry | |
| Radial velocity (Rv) | −17[8] km/s |
| Proper motion (μ) | RA: 198.8±0.20[2] mas/yr Dec.: −15±0.30[2] mas/yr |
| Parallax (π) | 7.54 ± 0.11 mas[2] |
| Distance | 323–433[9] ly (99–133[9] pc) |
| Absolute magnitude (MV) | −3.6 (α UMi Aa)[3] 3.6 (α UMi Ab)[3] 3.1 (α UMi B)[3] |
| Position (relative to α UMi Aa) | |
| Component | α UMi Ab |
| Epoch of observation | 2005.5880 |
| Angular distance | 0.172″ |
| Position angle | 231.4° |
| Position (relative to α UMi Aa) | |
| Component | α UMi B |
| Epoch of observation | 2005.5880 |
| Angular distance | 18.217″ |
| Position angle | 230.540° |
| Orbit[10] | |
| Primary | α UMi Aa |
| Companion | α UMi Ab |
| Period (P) | 29.59±0.02 yr |
| Semi-major axis (a) | 0.1204±0.0059" (≥2.90±0.03 AU[11]) |
| Eccentricity (e) | 0.608±0.005 |
| Inclination (i) | 146.2±10.9° |
| Longitude of the node (Ω) | 191.4±4.9° |
| Periastron epoch (T) | 1987.66±0.13 |
| Argument of periastron (ω) (secondary) | 123.01±0.75° |
| Semi-amplitude (K1) (primary) | 3.72±0.03 km/s |
| Details | |
| α UMi Aa | |
| Mass | 5.4[12] M☉ |
| Radius | 37.5[12] R☉ |
| Luminosity (bolometric) | 1,260[12] L☉ |
| Surface gravity (log g) | 2.2[13] cgs |
| Temperature | 6015[7] K |
| Metallicity | 112% solar[14] |
| Rotation | 119 days[6] |
| Rotational velocity (v sin i) | 14[6] km/s |
| Age | 45 - 67[15] Myr |
| α UMi Ab | |
| Mass | 1.26[3] M☉ |
| Radius | 1.04[3] R☉ |
| Luminosity (bolometric) | 3[3] L☉ |
| Age | >500[15] Myr |
| α UMi B | |
| Mass | 1.39[3] M☉ |
| Radius | 1.38[7] R☉ |
| Luminosity (bolometric) | 3.9[7] L☉ |
| Surface gravity (log g) | 4.3[7] cgs |
| Temperature | 6900[7] K |
| Rotational velocity (v sin i) | 110[7] km/s |
| Age | 1.5[15] Gyr |
| Other designations | |
Polaris, North Star, Cynosura, Alpha UMi, α UMi, ADS 1477, CCDM J02319+8915 | |
| α UMi A: 1 Ursae Minoris, BD+88°8, FK5 907, GC 2243, HD 8890, HIP 11767, HR 424, SAO 308 | |
| α UMi B: NSV 631, BD+88°7, GC 2226, SAO 305 | |
| Database references | |
| SIMBAD | α UMi A |
| α UMi B | |
Polaris is a star in the northern circumpolar constellation of Ursa Minor. It is designated α Ursae Minoris (Latinized to Alpha Ursae Minoris) and is commonly called the North Star or Pole Star. With an apparent magnitude that fluctuates around 1.98,[3] it is the brightest star in the constellation and is readily visible to the naked eye at night.[16] The position of the star lies less than 1° away from the north celestial pole, making it the current northern pole star. The stable position of the star in the Northern Sky makes it useful for navigation.
As the closest Cepheid variable its distance is used as part of the cosmic distance ladder. The revised Hipparcos stellar parallax gives a distance to Polaris of about 433 light-years (133 parsecs), while the successor mission Gaia gives a distance of about 448 light-years (137 parsecs). Calculations by other methods vary widely.
Although appearing to the naked eye as a single point of light, Polaris is a triple star system, composed of the primary, a yellow supergiant designated Polaris Aa, in orbit with a smaller companion, Polaris Ab; the pair is in a wider orbit with Polaris B. The outer pair AB were discovered in August 1779 by William Herschel, where the 'A' refers to what is now known to be the Aa/Ab pair.
- ^ "Polaris | meaning in the Cambridge English Dictionary". Cambridge English Dictionary. Retrieved 11 December 2020.
- ^ a b c d e Cite error: The named reference
hipparcos2was invoked but never defined (see the help page). - ^ a b c d e f g h i j k l m Evans, N. R.; Schaefer, G. H.; Bond, H. E.; Bono, G.; Karovska, M.; Nelan, E.; Sasselov, D.; Mason, B. D. (2008). "Direct Detection of the Close Companion of Polaris with The Hubble Space Telescope". The Astronomical Journal. 136 (3): 1137. arXiv:0806.4904. Bibcode:2008AJ....136.1137E. doi:10.1088/0004-6256/136/3/1137. S2CID 16966094.
- ^ a b c Samus, N. N.; Kazarovets, E. V.; et al. (2017). "General Catalogue of Variable Stars". Astronomy Reports. 5.1. 61 (1): 80–88. Bibcode:2017ARep...61...80S. doi:10.1134/S1063772917010085. S2CID 125853869.
- ^ a b Cite error: The named reference
Gaia_DR3was invoked but never defined (see the help page). - ^ a b c Lee, B. C.; Mkrtichian, D. E.; Han, I.; Park, M. G.; Kim, K. M. (2008). "Precise Radial Velocities of Polaris: Detection of Amplitude Growth". The Astronomical Journal. 135 (6): 2240. arXiv:0804.2793. Bibcode:2008AJ....135.2240L. doi:10.1088/0004-6256/135/6/2240. S2CID 12176373.
- ^ a b c d e f g h Usenko, I. A.; Klochkova, V. G. (2008). "Polaris B, an optical companion of the Polaris (α UMi) system: Atmospheric parameters, chemical composition, distance and mass". Monthly Notices of the Royal Astronomical Society: Letters. 387 (1): L1. arXiv:0708.0333. Bibcode:2008MNRAS.387L...1U. doi:10.1111/j.1745-3933.2008.00426.x. S2CID 18848139.
- ^ Campbell, William Wallace (1913). "The radial velocities of 915 stars". Lick Observatory Bulletin. 229: 113. Bibcode:1913LicOB...7..113C. doi:10.5479/ADS/bib/1913LicOB.7.113C.
- ^ a b Cite error: The named reference
turner2012was invoked but never defined (see the help page). - ^ Evans, N. R.; et al. (2018). "The Orbit of the Close Companion of Polaris: Hubble Space Telescope Imaging, 2007 to 2014". The Astrophysical Journal. 863 (2): 187. arXiv:1807.06115. Bibcode:2018ApJ...863..187E. doi:10.3847/1538-4357/aad410. S2CID 119392532.
- ^ Cite error: The named reference
Anderson2019was invoked but never defined (see the help page). - ^ a b c Fadeyev, Y. A. (2015). "Evolutionary status of Polaris". Monthly Notices of the Royal Astronomical Society. 449 (1): 1011–1017. arXiv:1502.06463. Bibcode:2015MNRAS.449.1011F. doi:10.1093/mnras/stv412. S2CID 118517157.
- ^ Usenko, I. A.; Miroshnichenko, A. S.; Klochkova, V. G.; Yushkin, M. V. (2005). "Polaris, the nearest Cepheid in the Galaxy: Atmosphere parameters, reddening and chemical composition". Monthly Notices of the Royal Astronomical Society. 362 (4): 1219. Bibcode:2005MNRAS.362.1219U. doi:10.1111/j.1365-2966.2005.09353.x.
- ^ Cayrel de Strobel, G.; Soubiran, C.; Ralite, N. (2001). "Catalogue of [Fe/H] determinations for FGK stars: 2001 edition". Astronomy and Astrophysics. 373: 159–163. arXiv:astro-ph/0106438. Bibcode:2001A&A...373..159C. doi:10.1051/0004-6361:20010525. S2CID 17519049.
- ^ a b c Neilson, H. R.; Blinn, H. (2021). The Curious Case of the North Star: The Continuing Tension Between Evolution Models and Measurements of Polaris. RR Lyrae/Cepheid 2019: Frontiers of Classical Pulsators. Vol. 529. p. 72. arXiv:2003.02326. Bibcode:2021ASPC..529...72N.
- ^ Kaler, Jim. "Polaris (Alpha Ursae Minoris)". Stars. Retrieved 2020-09-09.