Polaris
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] | |
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 | |
″ | ||
Position angle | 231.4° | |
Position (relative to α UMi Aa) | ||
Component | α UMi B | |
″ | ||
Position angle | 230.540° | |
Semi-amplitude (K1)(primary) | 3.72±0.03 km/s | |
Details | ||
α UMi Aa | ||
Myr | ||
α UMi Ab | ||
Gyr | ||
305 | ||
Database references | ||
SIMBAD | α UMi A | |
α UMi B |
Polaris is a
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.
Stellar system
Polaris Aa is an
The variable radial velocity of Polaris A was reported by W. W. Campbell in 1899, which suggested this star is a binary system.[21] Since Polaris A is a known cepheid variable, J. H. Moore in 1927 demonstrated that the changes in velocity along the line of sight were due to a combination of the four-day pulsation period combined with a much longer orbital period and a large eccentricity of around 0.6.[22] Moore published preliminary orbital elements of the system in 1929, giving an orbital period of about 29.7 years with an eccentricity of 0.63. This period was confirmed by proper motion studies performed by B. P. Gerasimovič in 1939.[23]
As part of her doctoral thesis, in 1955
There were once thought to be two more widely separated components—Polaris C and Polaris D—but these have been shown not to be physically associated with the Polaris system.[17][26]
Observation
Variability
Polaris Aa, the supergiant primary component, is a low-amplitude
The range of brightness of Polaris is given as 1.86–2.13,[4] but the amplitude has changed since discovery. Prior to 1963, the amplitude was over 0.1 magnitude and was very gradually decreasing. After 1966, it very rapidly decreased until it was less than 0.05 magnitude; since then, it has erratically varied near that range. It has been reported that the amplitude is now increasing again, a reversal not seen in any other Cepheid.[6]
The period, roughly 4 days, has also changed over time. It has steadily increased by around 4.5 seconds per year except for a hiatus in 1963–1965. This was originally thought to be due to secular redward (lower temperature) evolution across the Cepheid instability strip, but it may be due to interference between the primary and the first-overtone pulsation modes.[20][29][30] Authors disagree on whether Polaris is a fundamental or first-overtone pulsator and on whether it is crossing the instability strip for the first time or not.[12][30][31]
The temperature of Polaris varies by only a small amount during its pulsations, but the amount of this variation is variable and unpredictable. The erratic changes of temperature and the amplitude of temperature changes during each cycle, from less than 50 K to at least 170 K, may be related to the orbit with Polaris Ab.[13]
Research reported in
Role as pole star
Because Polaris lies nearly in a direct line with the Earth's rotational axis "above" the North Pole—the north celestial pole—Polaris stands almost motionless in the sky, and all the stars of the northern sky appear to rotate around it. Therefore, it makes an excellent fixed point from which to draw measurements for celestial navigation and for astrometry. The elevation of the star above the horizon gives the approximate latitude of the observer.[16]
In 2018 Polaris was 0.66° (39.6 arcminutes) away from the pole of rotation (1.4 times the
The apparent motion of Polaris towards and, in the future, away from the celestial pole, is due to the
The celestial pole was close to Thuban around 2750 BC,[35] and during classical antiquity it was slightly closer to Kochab (β UMi) than to Polaris, although still about 10° from either star.[36] It was about the same angular distance from β UMi as to α UMi by the end of late antiquity. The Greek navigator Pytheas in ca. 320 BC described the celestial pole as devoid of stars. However, as one of the brighter stars close to the celestial pole, Polaris was used for navigation at least from late antiquity, and described as ἀεί φανής (aei phanēs) "always visible" by Stobaeus (5th century), also termed Λύχνος (Lychnos) akin to a burner or lamp and would reasonably be described as stella polaris from about the High Middle Ages and onwards, both in Greek and Latin. On his first trans-Atlantic voyage in 1492, Christopher Columbus had to correct for the "circle described by the pole star about the pole".[37] In Shakespeare's play Julius Caesar, written around 1599, Caesar describes himself as being "as constant as the northern star", though in Caesar's time there was no constant northern star.
Polaris was referenced in
Names
The modern name Polaris
In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN)[41] to catalog and standardize proper names for stars. The WGSN's first bulletin of July 2016[42] included a table of the first two batches of names approved by the WGSN; which included Polaris for the star α Ursae Minoris Aa.
In antiquity, Polaris was not yet the closest naked-eye star to the celestial pole, and the entire constellation of
In the Hindu
An older English name, attested since the 14th century, is lodestar "guiding star", cognate with the Old Norse leiðarstjarna, Middle High German leitsterne.[46]The ancient name of the constellation Ursa Minor, Cynosura (from the Greek κυνόσουρα "the dog's tail"),[47] became associated with the pole star in particular by the early modern period. An explicit identification of Mary as stella maris with the polar star (Stella Polaris), as well as the use of Cynosura as a name of the star, is evident in the title Cynosura seu Mariana Stella Polaris (i.e. "Cynosure, or the Marian Polar Star"), a collection of Marian poetry published by Nicolaus Lucensis (Niccolo Barsotti de Lucca) in 1655. [citation needed]
Its name in traditional pre-Islamic Arab astronomy was al-Judayy الجدي ("the kid", in the sense of a juvenile goat ["le Chevreau"] in Description des Etoiles fixes),[48] and that name was used in medieval Islamic astronomy as well.[49][50] In those times, it was not yet as close to the north celestial pole as it is now, and used to rotate around the pole.
It was invoked as a symbol of steadfastness in poetry, as "steadfast star" by Spenser.
In Inuit astronomy, Polaris is known as Nuutuittuq (syllabics: ᓅᑐᐃᑦᑐᖅ). It is depicted on the flag and coat of arms of the Canadian Inuit territory of Nunavut, as well as on the flag of the U.S. state of Alaska.[51]
In traditional Lakota star knowledge, Polaris is named "Wičháȟpi Owáŋžila". This translates to "The Star that Sits Still". This name comes from a Lakota story in which he married Tȟapȟúŋ Šá Wíŋ, "Red Cheeked Woman". However, she fell from the heavens, and in his grief Wičháȟpi Owáŋžila stared down from "waŋkátu" (the above land) forever.[52]
The
In the ancient Finnish worldview, the North Star has also been called taivaannapa and naulatähti ("the nailstar") because it seems to be attached to the firmament or even to act as a fastener for the sky when other stars orbit it. Since the starry sky seemed to rotate around it, the firmament is thought of as a wheel, with the star as the pivot on its axis. The names derived from it were sky pin and world pin.[citation needed]
Distance
Many recent papers calculate the distance to Polaris at about 433
Year | Component | Distance, ly (pc) | Notes |
---|---|---|---|
2006 | A | 330 ly (101 pc) | Turner[29] |
2007[A] | A | 433 ly (133 pc) | Hipparcos[2] |
2008 | B | 359 ly (110 pc) | Usenko & Klochkova[7] |
2013 | B | 323 ly (99 pc) | Turner, et al.[9] |
2014 | A | ≥ 385 ly (≥ 118 pc) | Neilson[55] |
2018 | B | 521 ly (160pc) | Bond et al.[56] |
2018 | B | 445.3 ly (136.6 pc)[B] | Gaia DR2[57] |
2020 | B | 447.6 ly (137.2pc) | Gaia DR3[5] |
A New revision of observations from 1989–1993, first published in 1997 |
B Statistical distance calculated using a weak distance prior |
The Hipparcos spacecraft used
The next major step in high precision parallax measurements comes from
Gallery
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Polaris is the brightest star in the constellation of Ursa Minor (upper right).
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Big Dipper and Ursa Minor in relation to Polaris
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A view of Polaris in a small telescope. Polaris B is separated by 18 arc seconds from the primary star, Polaris A.
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A 4 day time lapse of Polaris illustrating its Cepheid type variability.
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Polaris pictured in the coat of arms of Utsjoki[citation needed]
See also
- Extraterrestrial sky (for the pole stars of other celestial bodies)
- Polar alignment
- Polaris Australis
- Polaris Flare
- Regiment of the North Pole
References
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- ^ Bibcode:2021ASPC..529...72N.
- ^ a b Kaler, Jim. "Polaris (Alpha Ursae Minoris)". Stars. Retrieved 2020-09-09.
- ^ Bibcode:2000A&A...360..399W.
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- ^ "A visual method to correct a ship's compass using Polaris using Ursa Major as a point of reference". Archived from the original on August 27, 2010. Retrieved Aug 7, 2016.
- ^ ISBN 978-0-13-145164-3.
Around 4800 years ago Thuban (α Draconis) lay a mere 0°.1 from the pole. Deneb (α Cygni) will be the brightest star near the pole in about 8000 years' time, at a distance of 7°.5.
- ^ Ridpath, Ian (2018). "Ursa Minor, the Little Bear". Star Tales. Retrieved 20 August 2016.
- ^ Columbus, Ferdinand (1960). The Life of the Admiral Christopher Columbus by His Son Fredinand. Translated by Keen, Benjamin. London: Folio Society. p. 74.
- ISBN 978-0-939837-54-0.
- ^ IAU Working Group on Star Names "IAU Catalog of Star Names". Retrieved 28 July 2016.
- ^ Gemmae Frisii de astrolabo catholico liber: quo latissime patentis instrumenti multiplex usus explicatur, & quicquid uspiam rerum mathematicarum tradi possit continetur. Steelsius. 1556. p. 20.;
see also Kunitzsch, Paul; Smart, Tim (2006). A Dictionary of Modern star Names: A Short Guide to 254 Star Names and Their Derivations (2nd rev. ed.). Cambridge, Massachusetts: ISBN 978-1-931559-44-7.
- ^ "International Astronomical Union | IAU". www.iau.org. Retrieved 2019-01-19.
- ^ "Bulletin of the IAU Working Group on Star Names, No. 1" (PDF).
- ^ Dickins, Bruce (1915). Runic and heroic poems of the old Teutonic peoples. p. 18.; Dickins' "a circumpolar constellation" is attributed to L. Botkine, La Chanson des Runes (1879).
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- ^ Halliwell, J. O., ed. (1856). The Works of William Shakespeare. Vol. 5. p. 40.
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- ^ ʻAbd al-Raḥmān ibn ʻUmar Ṣūfī (1874). Description des Etoiles fixes. Commissionnaires de lÁcadémie Impériale des sciences. p. 45.
- ^ Al-Sufi, AbdulRahman (964). "Book Of Fixed Stars".
- ^ Schjellerup, Hans (1874). Description des Etoiles fixes. p. 45.
- ^ "The Coat of Arms of Nunavut. (n.d.)". Legislative Assembly of Nunavut. Retrieved 2021-09-15.
- ^ "Winter Solstice is Sacred Time a Time to Carry One Another by Dakota Wind". 27 December 2019.
- ^ "Polaris". Plains Cree Dictionary. Retrieved 13 December 2022.
- ^ Lebans, Jim (29 September 2022). "Mi'kmaw astronomer says we should acknowledge we live under Indigenous skies". Canadian Broadcasting Corporation. Retrieved 21 December 2022.
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