Editing Arcturus (section)

{{Short description|Brightest star in the constellation Boötes}}
{{hatnote group|
{{other uses}}
{{redirect|α Boötis|A Boötis|HD 125351}}
}}
{{Use mdy dates|date=January 2025}}
{{Starbox begin}}
{{Starbox image
| image =
   {{Location mark
 | image=Boötes_IAU.svg
 | float=center | width=250 | position=right
 | mark=Red circle.svg | mark_width=14 | mark_link=α Boo
 | x%=56.2 | y%=62.8
   }}
| caption=Arcturus in the constellation of Boötes (circled)
}}
{{Starbox observe
 | epoch       =J2000
 | constell    =[[Boötes]]
 | pronounce   ={{IPAc-en|ɑːr|k|ˈ|tj|ʊər|ə|s|audio=LL-Q1860 (eng)-Naomi Persephone Amethyst (NaomiAmethyst)-Arcturus.wav}}
 | ra          ={{RA|14|15|39.7}}<ref name="vanLeeuwen2007"/>
 | dec         ={{DEC|+19|10|56}}<ref name="vanLeeuwen2007"/>
 | appmag_v    =−0.05<ref name=ducati/>
}}
{{Starbox character
 | class             = K1.5 III Fe−0.5<ref name=perkins/>
 | appmag_1_passband = [[J band (infrared)|J]]
 | appmag_1          = −2.25<ref name=ducati/>
 | b-v               = +1.23<ref name=ducati/>
 | u-b               = +1.28<ref name=ducati/>
 | r-i               = +0.65<ref name=ducati/>
 | v-r               =
 | variable          =
 | type              = [[Red giant branch]]<ref name=ramirez_prieto_2011/>
}}
|- bgcolor="#FFFAFA"
| Note (category: variability): || H and K emission vary.
{{Starbox astrometry
 | radial_v          =−5.19<ref name=massarotti2008/>
 | prop_mo_ra        ={{val|-1093.45}}<ref name=Perryman1997/>
 | prop_mo_dec       ={{val|-1999.40}}<ref name=Perryman1997/>
 | parallax          =88.83
 | p_error           =0.54
 | parallax_footnote =<ref name="vanLeeuwen2007"/>
 | absmag_v          ={{val|-0.30|0.02}}<ref name=aj135_3_892/>
}}
{{Starbox detail
 | mass                ={{val|1.08|0.06}}<ref name=ramirez_prieto_2011/>
 | metal_fe            ={{val|-0.52|0.04}}<ref name=ramirez_prieto_2011/>
 | radius              ={{val|25.4|0.2}}<ref name=ramirez_prieto_2011/>
 | rotational_velocity ={{val|2.4|1.0}}<ref name=aj135_3_892/>
 | luminosity          =170<ref name=aaa465_2_593/>
 | temperature         ={{val|4286|30|fmt=commas}}<ref name=ramirez_prieto_2011/>
 | gravity             ={{val|1.66|0.05}}<ref name=ramirez_prieto_2011/>
 | age_gyr             ={{val|7.1|+1.5|-1.2}}<ref name=ramirez_prieto_2011/>
}}
{{Starbox catalog
 | names={{odlist | name=Alramech | name2=Alramech | name3=Abramech | B=α&nbsp;Boötis, Alpha&nbsp;Boo, α&nbsp;Boo | F=16 Boötis | BD=+19°2777 | GJ=541 | HD=124897 | HIP=69673 | HR=5340 | SAO=100944 | GCTP=3242.00 | LHS=48 }}, [[General Catalogue of Trigonometric Parallaxes|GCTP]]&nbsp;3242.00
}}
{{Starbox reference
 | Simbad=HD+124897
 | ARICNS =
}}
{{starbox sources|HIP|CCDM|HR|[http://webviz.u-strasbg.fr/viz-bin/VizieR-S?HR%205340 VizieR catalog entry]}}
{{Starbox end}}

'''Arcturus''' is the brightest [[star]] in the [[Northern celestial hemisphere|northern]] [[constellation]] of [[Boötes]]. With an [[apparent visual magnitude]] of −0.05,<ref name=ducati/> it is the [[List of brightest stars|fourth-brightest]]  star in the [[night sky]], and the brightest in the [[northern celestial hemisphere]]. The name Arcturus originated from [[Ancient Greek astronomy|ancient Greece]]; it was then cataloged as '''α&nbsp;Boötis''' by [[Johann Bayer]] in 1603, which is [[Latinisation of names|Latinized]] to '''Alpha&nbsp;Boötis'''. Arcturus forms one corner of the [[Spring Triangle]] [[Asterism (astronomy)|asterism]].

Located relatively close at 36.7 [[light-year]]s from the [[Sun]], Arcturus is a [[red giant]] of [[Stellar classification|spectral type]] K1.5III—an aging star around 7.1 billion years old that has used up its [[Stellar core|core]] [[hydrogen]] and [[stellar evolution|evolved]] off the [[main sequence]]. It is about the same mass [[Solar mass|as the Sun]], but has expanded to 25 times [[Solar radius|its size]] (around 35 million kilometers) and is around 170 times as luminous.