Alioth
{{short description|Star in the constellation Ursa Major}}
{{Other uses}}
{{Starbox begin}}
{{Starbox image
| image=
{{Location mark
| image=Ursa Major constellation map.svg
| float=center | width=250 | position=right
| mark=Red circle.svg | mark_width=10 | mark_link=ε UMa
| x%=28.4 | y%=44.6
}}
| caption=Location of Alioth (circled)
}}
{{Starbox observe
| epoch = J2000
| dec = {{DEC|+55|57|35.3627}}
| constell = Ursa Major
}}
{{Starbox character
| class = A1III-IVp kB9
| variable = α2 CVn
}}
{{Starbox astrometry
| prop_mo_ra = +111.91
| prop_mo_dec = −8.24
| parallax = 39.51
| p_error = 0.20
}}
{{Starbox detail
| radius = {{val|4.29|0.19|0.21}}
| luminosity = {{val|104.4|9.3}}
| temperature = {{val|8908|24|fmt=commas}}
}}
{{Starbox catalog
| names = {{odlist | name=Alioth, Allioth, Aliath | B=ε UMa | F=77 Ursae Majoris | BD=+56°1627 | FK5=483 | GC=17518 | HD=112185 | HIP=62956 | HR=4905 | PPM=33769 | SAO=28553 }}
}}
{{Starbox reference
| Simbad = ALIOTH
}}
{{Starbox end}}
Alioth {{IPAc-en|'|æ|l|i|Q|θ|audio=LL-Q1860 (eng)-Naomi Persephone Amethyst (NaomiAmethyst)-Alioth.wav}}, also called Epsilon Ursae Majoris, is a star in the northern constellation of Ursa Major. The designation is Latinised from ε Ursae Majoris and abbreviated Epsilon UMa or ε UMa.{{cite book
|last1=Kunitzsch |first1=Paul
|last2=Smart |first2=Tim
|date = 2006 |edition = 2nd rev.
|title = A Dictionary of Modern star Names: A Short Guide to 254 Star Names and Their Derivations
|publisher = Sky Pub |location = Cambridge, Massachusetts
|isbn = 978-1-931559-44-7
}}{{cite web | url=http://www.pas.rochester.edu/~emamajek/WGSN/IAU-CSN.txt | title=IAU Catalog of Star Names |access-date=28 July 2016}} Despite being designated "ε" (epsilon), it is the brightest star in the constellation and at magnitude 1.77 is the thirty-third brightest star in the sky.
It is the star in the tail of the bear closest to its body, and thus the star in the handle of the Big Dipper (or Plough) closest to the bowl. It is also a member of the large and diffuse Ursa Major moving group. Historically, the star was frequently used in celestial navigation in the maritime trade, because it is listed as one of the 57 navigational stars.{{ref label|1728|1|^}}
Physical characteristics
Image:Sidney Hall - Urania's Mirror - Ursa Major.jpg depicting Ursa Major's stars]]
File:EpsUMaLightCurve.png for Epsilon Ursae Majoris, plotted from TESS data]]
According to Hipparcos, Epsilon Ursae Majoris is {{convert|81|ly|pc|abbr=off|lk=on}} from the Sun. Its spectral type is A1p; the "p" stands for peculiar, as its spectrum is characteristic of an α2 Canum Venaticorum variable. Epsilon Ursae Majoris, as a representative of this type, may harbor two interacting processes: first, the star's strong magnetic field separating different elements in its hydrogen 'fuel'; second, a rotation axis at an angle to the magnetic axis may be spinning different bands of magnetically sorted elements into the line of sight between Epsilon Ursae Majoris and the Earth. The intervening elements react differently at different frequencies of light as they whip in and out of view, causing Epsilon Ursae Majoris to have very strange spectral lines that fluctuate over a period of 5.1 days. The kB9 suffix to the spectral type indicates that the calcium K line is present and representative of a B9 spectral type even though the rest of the spectrum indicates A1.
Epsilon Ursae Majoris's rotational and magnetic poles are at almost 90 degrees to one another. Darker (denser) regions of chromium form a band at right angles to the equator.
It has long been suspected that Epsilon Ursae Majoris is a spectroscopic binary, possibly with more than one companion. A more recent study suggests Epsilon Ursae Majoris's 5.1-day variation may be due to a substellar object of about 14.7 Jupiter masses in an eccentric orbit (e=0.5) with an average separation of 0.055 astronomical units. It is now thought that the 5.1-day period is the rotation period of the star, and no companions have been detected using the most modern equipment. Observations of Alioth with the Navy Precision Optical Interferometer also did not detect a companion.
Epsilon Ursae Majoris has a relatively weak magnetic field for a variable of this type, 15 times weaker than α Canum Venaticorum, but it is still 100 times stronger than that of the Earth.
Name and etymology
ε Ursae Majoris (Latinised to Epsilon Ursae Majoris) is the star's Bayer designation.
The traditional name Alioth comes from the Arabic alyat al-hamal ("the sheep's fat tail"). In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN){{cite web | url=https://www.iau.org/science/scientific_bodies/working_groups/280/ | title=IAU Working Group on Star Names (WGSN)|access-date=22 May 2016}} to catalog and standardize proper names for stars. The WGSN's first bulletin of July 2016{{cite web | url=http://www.pas.rochester.edu/~emamajek/WGSN/WGSN_bulletin1.pdf |archive-url=https://ghostarchive.org/archive/20221009/http://www.pas.rochester.edu/~emamajek/WGSN/WGSN_bulletin1.pdf |archive-date=2022-10-09 |url-status=live | title=Bulletin of the IAU Working Group on Star Names, No. 1 |access-date=28 July 2016}} included a table of the first two batches of names approved by the WGSN; which included Alioth for this star.
This star was known to the Hindus as Añgiras, one of the Seven Rishis.{{cite book
| last=Allen
| first=R. H.
| year=1963
| author-link=Richard Hinckley Allen
| title=Star Names: Their Lore and Meaning
| url=https://archive.org/details/starnamestheirlo00alle/page/438
| access-date=2012-09-04
| edition=Reprint
| publisher=Dover Publications Inc
| location=New York
| isbn=0-486-21079-0
| page=[https://archive.org/details/starnamestheirlo00alle/page/438 438]
| url-access=registration
}}
In Chinese, {{lang|zh|北斗}} ({{lang|zh-Latn|Běi Dǒu}}), meaning Northern Dipper, refers to an asterism equivalent to the Big Dipper. Consequently, the Chinese name for Epsilon Ursae Majoris itself is {{lang|zh|北斗五}} ({{lang|zh-Latn|Běi Dǒu wu}}, {{langx|en|the Fifth Star of Northern Dipper}}) and {{lang|zh|玉衡}} ({{lang|zh-Latn|Yù Héng}}, {{langx|en|Star of Jade Sighting-Tube}}).{{in lang|zh}} [http://aeea.nmns.edu.tw/2006/0606/ap060615.html AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 6 月 15 日] {{Webarchive|url=https://web.archive.org/web/20141102063635/http://aeea.nmns.edu.tw/2006/0606/ap060615.html |date=2014-11-02 }}
Namesakes
The United States Navy's Crater class cargo ship {{USS|Allioth|AK-109}} was named after the star.
See also
References
{{reflist|refs=
<
{{citation | last=Evans | first=D. S. | date=June 20–24, 1966 | editor1-last=Batten | editor1-first=Alan Henry | editor2-last=Heard | editor2-first=John Frederick | title=The Revision of the General Catalogue of Radial Velocities | volume=30 | pages=57 | work=Determination of Radial Velocities and their Applications, Proceedings from IAU Symposium no. 30 | location=University of Toronto | publisher=International Astronomical Union | bibcode=1967IAUS...30...57E }}
| last1 = Sokolov
| first1 = N. A.
| title = Radial velocity study of the chemically peculiar star ɛ Ursae Majoris
| journal = Monthly Notices of the Royal Astronomical Society: Letters
| volume = 385
| issue = 1
| pages = L1–L4
|date=March 2008
| doi = 10.1111/j.1745-3933.2008.00419.x
| doi-access = free
| bibcode = 2008MNRAS.385L...1S
| arxiv = 0904.3562
| s2cid = 17104356
| postscript = .
}}
}}
- {{note label|1728|1|^}}{{1728|title=Allioth}}
{{Stars of Ursa Major}}
{{Portal bar|Astronomy|Stars|Outer space}}
Category:Alpha2 Canum Venaticorum variables