View source for Astronomy:Epsilon Draconis

{{Short description|Star in the constellation Draco}}
{{Starbox begin}}
{{Starbox image
| image=
   {{Location mark
     | image=Draco constellation map.svg
     | float=center | width=250 | position=right
     | mark=Red circle.svg | mark_width=10 | mark_link=Epsilon Dra
     | x%=16.6 | y%=40.6
   }}
| caption=Location of ε Draconis (circled)
}}
{{Starbox observe
 |epoch=J2000
  | ra={{RA|19|48|10.34973}}<ref name=GaiaDR2>{{Cite Gaia DR2|2251191616253487360}}</ref>
  | dec={{DEC|70|16|04.5329}}<ref name=GaiaDR2/>
  | appmag_v=3.9974<ref name="LEEUWEN"/>
  | constell=[[Astronomy:Draco (constellation)|Draco]]
}}
{{Starbox character
  | class=G7IIIbFe-1<ref name=Keenan_McNeil_1989>{{cite journal | bibcode=1989ApJS...71..245K | title=The Perkins catalog of revised MK types for the cooler stars | journal=Astrophysical Journal Supplement Series | volume=71 | pages=245 | last1=Keenan | first1=Philip C. | last2=McNeil | first2=Raymond C. | year=1989 | doi=10.1086/191373 }}</ref>
 | b-v=+0.88 <ref name="MERMILLIOD">{{cite journal
  | author=Mermilliod, J.-C.
  | title=Compilation of Eggen's UBV data, transformed to UBV (unpublished)
  | journal=Catalogue of Eggen's UBV Data. SIMBAD
  | year=1986
  | bibcode=1986EgUBV........0M}}</ref>
  |u-b=+0.48<ref name="MERMILLIOD"/>
  | variable= 
}}
{{Starbox astrometry 
  |radial_v={{val|+2.69|0.23}}<ref name=Soubiran_et_al_2008>{{cite journal | display-authors=1 | last1=Soubiran | first1=C. | last2=Bienaymé | first2=O. | last3=Mishenina | first3=T. V. | last4=Kovtyukh | first4=V. V. | title=Vertical distribution of Galactic disk stars. IV. AMR and AVR from clump giants | journal=Astronomy and Astrophysics | year=2008 | volume=480 | issue=1 | pages=91–101 | bibcode=2008A&A...480...91S | doi=10.1051/0004-6361:20078788 |arxiv = 0712.1370 | s2cid=16602121 }}</ref>
  |prop_mo_ra=+79.702<ref name=GaiaDR2/>
  |prop_mo_dec=+41.078<ref name=GaiaDR2/>
  |parallax=21.2526
  |p_error=0.3016
  |parallax_footnote=<ref name=GaiaDR2/>
  |absmag_v=0.71<ref name="LEEUWEN">{{cite journal
    | title=Hipparcos, the New Reduction
    | author=van Leeuwen, F
    |date=November 2007
    | pages=653–664
    | issue=2
    | volume=474 
    | url=http://vizier.u-strasbg.fr/viz-bin/VizieR-S?HIP%2068756
    | doi=10.1051/0004-6361:20078357
    | journal=Astronomy and Astrophysics 
    | bibcode=2007A&A...474..653V
    | access-date=2010-12-18|arxiv = 0708.1752 | s2cid=18759600
 }}</ref>
}}
{{Starbox detail 
 |mass=2.7<ref name="MALLIK1">{{cite journal
  | title=Li abundances and velocities in F and G stars
  |author1=Mallik, Sushma V. |author2=Parthasarathy, M. |author3=Pati, A. K. |date=October 2003
  | journal=[[Astronomy:VizieR|VizieR]] 
  | publisher=Centre de Données astronomiques de Strasbourg 
  | url=http://webviz.u-strasbg.fr/viz-bin/VizieR-5?-out.add=.&-source=J/A%2bA/409/251/table1&recno=121
  | access-date=2010-12-18}}</ref><ref name="MALLIK2">{{cite journal
    | title=Lithium and rotation in F and G dwarfs and subgiants
    |author1=Mallik, Sushma V. |author2=Parthasarathy, M. |author3=Pati, A. K. |date=October 2003
    | journal=Astronomy and Astrophysics
    | volume=409
    | issue=1
    | pages=251–261
    | url=http://www.aanda.org/index.php?option=com_article&access=bibcode&Itemid=129&bibcode=2003A%2526A...409..251MFUL
    | doi=10.1051/0004-6361:20031084
    | bibcode=2003A&A...409..251M
    | access-date=2010-12-18| doi-access=free
    }}</ref>
 |radius={{val|11.15|0.47|0.56}}<ref name=GaiaDR2/>
 |luminosity={{val|69.6|1.12}}<ref name=GaiaDR2/>
 |temperature={{val|4993|129|103}}<ref name=GaiaDR2/>
 |metal_fe=-0.31<ref name="SOUBIRIAN">{{cite journal
   |author1    = Soubiran, C.
   |author2    = Bienaymé, O.
   |author3    = Mishenina, T. V.
   |author4    = Kovtyukh, V. V.
   |title      = Vertical distribution of Galactic disk stars. IV. AMR and AVR from clump giants
   |journal    = Astronomy and Astrophysics
   |year       = 2008
   |volume     = 480
   |issue      = 1
   |pages      = 91–101
   |bibcode    = 2008A&A...480...91S
   |doi        = 10.1051/0004-6361:20078788
   |arxiv      = 0712.1370
   |s2cid      = 16602121
 }}</ref>
 |gravity=
 |rotational_velocity=1.2 <ref name="MALLIK1"/>
 |age_myr= 500<ref name="MALLIK1"/>
}}
{{Starbox catalog
 | names = {{odlist | name=Tyl | B=ε Dra | F=63&nbsp;Dra | HR=7582 | AG=+70°&nbsp;689 | BD=+69°&nbsp;1070 | HD=188119 | HIP=97433 | PLX=4689 | SAO=9540 | GC=27471 | CCDM=J19482+7016AB | 2MASS=J19481035+7016045 | IRAS=19483+7008 }}<ref name="SIMBAD">{{cite simbad
  | title=* eps Dra
  | access-date=2010-12-18}}</ref>
}}
{{Starbox reference
 |Simbad=HD+188119}}
{{Starbox end}}	

'''Epsilon Draconis''', [[Social:Romanization of Greek|Latinized]] from ε Draconis, is a fourth-magnitude [[Astronomy:Star|star]] in the [[Astronomy:Constellation|constellation]] [[Astronomy:Draco (constellation)|Draco]]. This star along with [[Astronomy:Delta Draconis|Delta Draconis]] (Altais), [[Astronomy:Pi Draconis|Pi Draconis]] and [[Astronomy:Rho Draconis|Rho Draconis]] forms an [[Astronomy:Asterism|asterism]] known as Al Tāis, meaning "the Goat".<ref>{{cite book
 | last=Allen
 | first=R. H.
 | year=1963
 | title=Star Names: Their Lore and Meaning
 | url=https://archive.org/details/starnamestheirlo00alle/page/209
 | access-date=2010-12-12
 | edition=Reprint
 | publisher=Dover Publications Inc
 | location=New York, NY
 | isbn=0-486-21079-0
 | page=[https://archive.org/details/starnamestheirlo00alle/page/209 209]
 | url-access=registration
 }}</ref>

In [[Astronomy:Chinese astronomy|Chinese astronomy]], {{lang|zh|天廚}} ({{lang|zh-Latn|Tiān Chú}}), meaning the [[Astronomy:Purple Forbidden enclosure|Celestial Kitchen]], refers to an asterism consisting of Epsilon Draconis, [[Astronomy:Delta Draconis|Delta Draconis]], [[Astronomy:Sigma Draconis|Sigma Draconis]],  Rho Draconis, [[Astronomy:64 Draconis|64 Draconis]] and Pi Draconis.<ref>{{in lang|zh}} ''中國星座神話'', written by 陳久金. Published by 台灣書房出版有限公司, 2005, {{ISBN|978-986-7332-25-7}}.</ref> Consequently, the [[Astronomy:Chinese star names|Chinese name]] for Epsilon Draconis itself is {{lang|zh|天廚三}} ({{lang|zh-Latn|Tiān Chú sān}}, {{lang-en|the Third Star of the Celestial Kitchen}}.)<ref>{{in lang|zh}} [http://www.lcsd.gov.hk/CE/Museum/Space/Research/StarName/c_research_chinengstars_t_z.htm 香港太空館 - 研究資源 - 亮星中英對照表] {{webarchive |url=https://web.archive.org/web/20100819122914/http://www.lcsd.gov.hk/CE/Museum/Space/Research/StarName/c_research_chinengstars_t_z.htm |date=August 19, 2010 }}, Hong Kong Space Museum. Accessed on line November 23, 2010.</ref> Most authors do not use a traditional name for this star, using instead the [[Astronomy:Bayer designation|Bayer designation]];<ref>{{cite web
  |title=Epsilon Draconis
  |first=Jim|last=Kaler
  |url=http://stars.astro.illinois.edu/sow/epsdra.html
  |access-date=2016-11-24}}</ref> 
but Bečvář (1951) listed it as '''Tyl''' {{IPAc-en|'|t|I|l}}.<ref name=Kunitzsch>{{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
}}</ref><ref>{{cite book
 |last=Bakich
 |first=Michael
 |date=1995
 |title=The Cambridge Guide to the Constellations
 |url=https://archive.org/details/cambridgeguideto00baki
 |url-access=registration
 |quote=Tyl.
 |publisher={{wipe|Cambridge University Press}}
 |page=[https://archive.org/details/cambridgeguideto00baki/page/202 202]
 |access-date=2016-11-24
 |isbn=0521449219}}</ref>

== Visibility ==
With a declination in excess of 70 degrees north, Epsilon Draconis is principally visible in the northern hemisphere, with southern locations north of 20° South able to see it just above the horizon.  The star is [[Astronomy:Circumpolar star|circumpolar]] throughout all of [[Earth:Europe|Europe]], {{wipe|China}}, most of {{wipe|India}} and as far south as the tip of the Baja peninsula in [[Earth:North America|North America]] as well as other locations around the globe having a latitude greater than ± 20° North.  Since Epsilon Draconis has an apparent magnitude of almost 4.0, the star is easily observable to the naked eye as long as one's stargazing is not hampered by the [[Astronomy:Light pollution|light pollution]] common to most cities.

The best time for observation is in the evening sky during the summer months, when the "Dragon constellation" passes the meridian at midnight, but given its circumpolar nature in the northern hemisphere, it is visible to most of the world's inhabitants throughout the year.

== Properties ==
Epsilon Draconis is a [[Astronomy:Giant star|yellow giant]] star with a [[Astronomy:Stellar classification|spectral type]] of G8III. It has a radius that has been estimated at 11 [[Astronomy:Solar radius|solar radii]] and a mass of 2.7 [[Astronomy:Solar mass|solar mass]]es.<ref name="MALLIK1"/>  Compared to most [[Astronomy:Stellar classification#Class G|G class]] stars, Epsilon Draconis is a relatively young star with an estimated age of around 500 million years old.<ref name="MALLIK1"/> Like the majority of giant stars, Epsilon Draconis rotates slowly on its axis with a rotational velocity of 1.2&nbsp;km/s, a speed which takes the star approximately 420 days to make one complete revolution.<ref name="MALLIK1"/>

In 2007, Floor van Leeuwen and his team calibrated the star's [[Astronomy:Apparent magnitude|apparent magnitude]] at 3.9974 with an updated parallax of 22.04 ± 0.37 milliarcseconds, yielding a distance of 45.4&nbsp;parsecs or approximately 148 [[Light year|light year]]s from [[Astronomy:Earth|Earth]].<ref name="LEEUWEN"/>  Given a surface temperature of 5,068 Kelvin, theoretical calculations would yield a total luminosity for the star of about 60 times the [[Astronomy:Solar luminosity|solar luminosity]].

== Star system ==
Epsilon Draconis is resolvable as a [[Astronomy:Double star|double star]] in telescopes of 10 centimeters aperture or larger. The companion has an apparent brightness of 7.3 at an [[Astronomy:Angular distance|angular distance]] of 3.2 [[Arcsecond|arcsecond]]s. It is a giant of spectral class F5,<ref name="SIMBAD"/> orbiting the yellow giant at about 130 [[Astronomy:Astronomical unit|astronomical unit]]s.{{cn|date=July 2021}}

== See also ==
* [[Astronomy:Lists of stars|Lists of stars]] in the constellation [[Astronomy:List of stars in Draco|Draco]]
* [[Astronomy:Stellar classification#Class G|Class G Stars]]
* [[Astronomy:Variable star|Variable star]]
* [[Astronomy:Double star|Double star]]

== References ==
{{reflist}}

== External links ==
*Astrophotographs:[http://www.asociacionhubble.org/portal/index.php/foro/viewtopic.php?f=63&t=16459&start=50 Epsilon Draconis]
*SkyView Image: [http://skyview.gsfc.nasa.gov/cgi-bin/nnskcall.pl?VCOORD=297.0431337500000382,+70.2679302777777792&SURVEY=Digitized+Sky+Survey&SCOORD=&EQUINX=2000&LUT=colortables/stern-special.bin Epsilon Draconis]
 
{{Stars of Draco}}
{{Sky|19|48|10.35|+|70|16|04.55|100000}}

{{DEFAULTSORT:Epsilon Draconis}}
<!-- Properties -->
[[Category:G-type giants]]
[[Category:Double stars]]
<!-- Other -->
[[Category:Draco (constellation)]]
[[Category:Bayer objects|Draconis, Epsilon]]
[[Category:Durchmusterung objects|BD+69 1070]]
[[Category:Flamsteed objects|Draconis, 63]]
[[Category:Henry Draper Catalogue objects|188119]]
[[Category:Hipparcos objects|097433]]
[[Category:Bright Star Catalogue objects|7582]]
[[Category:Stars with proper names|Tyl]]

{{Sourceattribution|Epsilon Draconis}}