Alpha Cassiopeiae

{{short description|Star in the constellation Cassiopeia}} {{about|α Cassiopeiae|A Cassiopeiae|48 Cassiopeiae}} {{Starbox begin | name=α Cassiopeiae }} {{Starbox image | image = {{Location mark | image=Cassiopeia constellation map.svg | float=center | width=240 | position=right | mark=Red circle.svg | mark_width=10 | mark_link=α Cas | x%=45.8 | y%=61.2 }} | caption = Location of α Cassiopeiae (circled) }} {{Starbox observe | epoch=J2000 | ra={{RA|00|40|30.4411}}<ref name="LEEUWEN"/> | dec={{DEC|+56|32|14.392}}<ref name="LEEUWEN"/> | appmag_v=2.240<ref name="KHARCHENKO">{{cite journal | title=All-sky Compiled Catalogue of 2.5 million stars | last1=Kharchenko | first1=N. V. | last2=Roeser | first2=S. | date=September 2009 | journal=VizieR | publisher=Centre de Données astronomiques de Strasbourg | url=http://vizier.u-strasbg.fr/viz-bin/VizieR-5?-out.add=.&-source=I/280B/ascc&recno=158513 | bibcode=2009yCat.1280....0K | access-date=2011-01-06}}</ref> | constell=Cassiopeia<ref name=xhip>{{cite XHIP | 3179 }}</ref> }} {{Starbox character | type = horizontal branch<ref name=reffert2015/> | class=K0-IIIa<ref name=perkins>{{cite journal | last1=Keenan | first1=Philip C. | last2=McNeil | first2=Raymond C. | title=The Perkins catalog of revised MK types for the cooler stars | journal=Astrophysical Journal Supplement Series | volume=71 | pages=245 | year=1989 | bibcode=1989ApJS...71..245K | doi=10.1086/191373 }}</ref> | b-v=1.170<ref name=xhip/> | u-b=1.14<ref name="MERMILLIOD">{{cite journal | last=Mermilliod | first=J.-C. | title=Compilation of Eggen's UBV data, transformed to UBV (unpublished) | journal=Catalogue of Eggen's UBV Data | date=1986 | bibcode=1986EgUBV........0M}}</ref> | variable=Suspected<ref name=gcvs>{{cite journal|bibcode=2009yCat....102025S|title=VizieR Online Data Catalog: General Catalogue of Variable Stars (Samus+ 2007-2013)|journal=VizieR On-line Data Catalog: B/GCVS. Originally Published in: 2009yCat....102025S|volume=1|display-authors=etal|last1=Samus|first1=N. N.|last2=Durlevich|first2=O. V.|year=2009}}</ref> }} {{Starbox astrometry | radial_v=−4.31 | prop_mo_ra=50.88<ref name="LEEUWEN"/> | prop_mo_dec=−32.13<ref name="LEEUWEN"/> | parallax=14.29 | p_error=0.15 | parallax_footnote=<ref name="LEEUWEN">{{cite journal | title=Hipparcos, the New Reduction | author=van Leeuwen, F | date=November 2007 | pages=653–664 | issue=2 | volume=474 | doi=10.1051/0004-6361:20078357 | journal=Astronomy and Astrophysics | bibcode=2007A&A...474..653V | arxiv = 0708.1752 | s2cid=18759600 }}</ref> | absmag_v=−2.01<ref name=katz2011>{{cite journal |bibcode=2011A&A...525A..90K |title=Probing the Galactic thick disc vertical properties and interfaces | display-authors=1 |last1=Katz |first1=D. |last2=Soubiran |first2=C. |last3=Cayrel |first3=R. |last4=Barbuy |first4=B. |last5=Friel |first5=E. |last6=Bienaymé |first6=O. |last7=Perrin |first7=M. -N. |journal=Astronomy and Astrophysics |year=2011 |volume=525 |pages=A90 |doi=10.1051/0004-6361/201014840 |doi-access=free }}</ref> }} {{Starbox detail | mass={{Val|4.98|0.45}}<ref name=Rudrasingam2026>{{cite journal |last=Rudrasingam |first=Jonatan |last2=Bedding |first2=Timothy R. |last3=Pope |first3=Benjamin J. S. |last4=Pedersen |first4=May Gade |last5=Lund |first5=Mikkel N. |last6=White |first6=Timothy R. |last7=Hey |first7=Daniel |title=Halo Photometry and Asteroseismology for 98 of the Brightest Stars Observed by TESS |date=2026-02-25 |arxiv=2602.22472 |journal=Monthly Notices of the Royal Astronomical Society }}</ref> | radius={{val|42.15|1.45|1.55}}<ref name=Baines2025>{{cite journal | display-authors=1 |last1=Baines |first1=Ellyn K. |last2=Clark |first2=James H. |last3=Kingsley |first3=Bradley I. |last4=Schmitt |first4=Henrique R. |last5=Stone |first5=Jordan M. |date=June 2025 |title=Vintage NPOI: New and Updated Angular Diameters for 145 Stars |journal=The Astronomical Journal |language=en |volume=169 |issue=6 |pages=293 |doi=10.3847/1538-3881/adc930 |doi-access=free |bibcode=2025AJ....169..293B |arxiv=2506.02912 |issn=1538-3881}}</ref> | luminosity={{val|734|52}}<ref name="npoi">{{Cite journal | display-authors=1 |last1=Baines |first1=Ellyn K. |last2=Clark III|first2=James H. |last3=Schmitt |first3=Henrique R. |last4=Stone |first4=Jordan M. |last5=von Braun |first5=Kaspar |date=2023-12-01 |title=33 New Stellar Angular Diameters from the NPOI, and Nearly 180 NPOI Diameters as an Ensemble |journal=The Astronomical Journal |volume=166 |issue=6 |pages=268 |doi=10.3847/1538-3881/ad08be |doi-access=free |bibcode=2023AJ....166..268B |issn=0004-6256|arxiv=2505.23514 }}</ref> | temperature={{val|4625|42|fmt=commas}}<ref name=Baines2025/> | gravity=1.73<ref name=reffert2015>{{cite journal |bibcode=2015A&A...574A.116R |title=Precise radial velocities of giant stars. VII. Occurrence rate of giant extrasolar planets as a function of mass and metallicity | display-authors=1 |last1=Reffert |first1=Sabine |last2=Bergmann |first2=Christoph |last3=Quirrenbach |first3=Andreas |last4=Trifonov |first4=Trifon |last5=Künstler |first5=Andreas |journal=Astronomy and Astrophysics |year=2015 |volume=574 |pages=A116 |doi=10.1051/0004-6361/201322360 |arxiv=1412.4634 |s2cid=59334290 }}</ref> | metal_fe=–0.2<ref name=reffert2015/> | rotational_velocity=6.71<ref name=hekker2007>{{cite journal |bibcode=2007A&A...475.1003H |title=Precise radial velocities of giant stars. III. Spectroscopic stellar parameters |last1=Hekker |first1=S. |last2=Meléndez |first2=J. |journal=Astronomy and Astrophysics |year=2007 |volume=475 |issue=3 |page=1003 |doi=10.1051/0004-6361:20078233 |arxiv=0709.1145 |s2cid=10436552 }}</ref> | age_myr=220<ref name=reffert2015/> }} {{Starbox catalog | names = {{odlist | name=Schedar | B=α Cas, Alpha Cas | F=18 Cas | HR=168 | BD=+55°139 | HD=3712 | SAO=21609 | FK5=21 | HIP=3179 | GC=792 | ADS=561 | CCDM=J00405+5632 | WDS=J00405+5632A }} }} {{Starbox reference | Simbad=SCHEDAR }} {{Starbox end}}

'''Alpha Cassiopeiae''' is a star in the northern constellation of Cassiopeia. It has the proper name '''Schedar''', pronounced {{IPAc-en|'|sh|E|d|ɑr}});<ref>{{MW|Schedar}}</ref><ref name="IAU-LSN">{{cite web | url=https://www.iau.org/public/themes/naming_stars/ | title=Naming Stars |publisher=IAU.org |access-date=18 June 2018}}</ref> ''Alpha Cassiopeiae'' is its Bayer designation, which is Latinized from '''α Cassiopeiae''' and abbreviated Alpha Cas or α Cas. Though listed as the "alpha star" by Johann Bayer, α Cas's visual brightness closely matches the 'beta' (β) star in the constellation (Beta Cassiopeiae) and it may appear marginally brighter or dimmer, depending on which passband is used. However, recent calculations from NASA's WISE telescope confirm that α Cas is the brightest in Cassiopeia, with an apparent magnitude of 2.240.{{cn|date=September 2025}} Its absolute magnitude is 18 times greater than β Cas, and it is located over four times farther away from the Sun.

== Nomenclature ==

''α Cassiopeiae'' (Latinised to ''Alpha Cassiopeiae'') is the star's Bayer designation.

It bore the traditional name ''Schedar'', which was first encountered in the Alfonsine tables of the thirteenth century. It derives from the Arabic word صدر ''şadr'', meaning "breast" (as in chest), a word which is derived from its relative position in the heart of the mythological queen Cassiopeia.<ref name="ALLEN">{{Cite web | title=Star Names: Their Lore and Meaning | publisher=Dover Publications | author=Richard Hinckley Allen | author-link=Richard Hinckley Allen | page=142 | date=1963 | access-date=2010-12-31 |url=https://penelope.uchicago.edu/Thayer/E/Gazetteer/Topics/astronomy/_Texts/secondary/ALLSTA/Cassiopeia*.html}}</ref> Johannes Hevelius used the name ''Schedir'' in his writings, although there were additional traditional spellings of this Arabic transliteration such as ''Shedar'', ''Shadar'', ''Sheder'', ''Seder'', ''Shedis'', and ''Shedir''. In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN)<ref name="WGSN">{{cite web | url=https://www.iau.org/science/scientific_bodies/working_groups/280/ | title=IAU Working Group on Star Names (WGSN) | publisher=International Astronomical Union | access-date=22 May 2016}}</ref> to catalogue and standardize proper names for stars. The WGSN approved the name ''Schedar'' for this star on 21 August 2016 and it is now so included in the List of IAU-approved Star Names.<ref name="IAU-LSN"/>

Al-Sufi and Ulug Beg named the star ''Al Dhāt al Kursiyy'' (Arabic ذات الكرسي, meaning "the lady in the chair"), which Giovanni Battista Riccioli changed to ''Dath Elkarti''.<ref name="ALLEN"/>

In Chinese, {{lang|zh|王良}} ({{lang|zh-Latn|Wáng Liáng}}) refers to the Chinese asterism ''Wang Liang'', a famous charioteer during the Spring and Autumn period. The stellar pattern consists of Alpha, Beta, Kappa, Eta and Lambda Cassiopeiae.<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 Chinese name for Alpha Cassiopeiae itself is {{lang|zh|王良四}} ({{lang|zh-Latn|Wáng Liáng sì}}, {{langx|en|the Fourth Star of Wang Liang}}).<ref>{{in lang|zh}} [http://www.lcsd.gov.hk/CE/Museum/Space/Research/StarName/c_research_chinengstars_s.htm 香港太空館 - 研究資源 - 亮星中英對照表] {{webarchive|url=https://web.archive.org/web/20100818141141/http://www.lcsd.gov.hk/CE/Museum/Space/Research/StarName/c_research_chinengstars_s.htm |date=2010-08-18 }}, Hong Kong Space Museum. Accessed on line November 23, 2010.</ref>

== Visibility == [[File:Cassiopeia in Milky Way.png|thumb|left|upright=1.2| Cassiopeia in the context of the Milky Way]] With a declination of 56° 32' North, α Cassiopeiae is principally visible in the Northern Hemisphere. The star is detectable to most observers across the globe reaching as far south as Perth, Australia, Santiago, Chile and other settlements north ± 33° South latitude, albeit close to the horizon. α Cassiopeiae is located in line-of-sight of the Milky Way galaxy, so there are other notable celestial objects that can be viewed close to this star—such as the Pacman Nebula, NGC 436 and NGC 457.

Alpha Cas reaches its zenith above cities like Edinburgh, Copenhagen and Moscow. It is circumpolar throughout Europe, Russia, and as far south as Los Angeles, California on the North American continent as well as other locations around the globe having a latitude greater than ± 33° North. Since α Cassiopeiae is listed as a second-magnitude star (equal to Beta Cas), it is easily observable to the naked eye as long as one's stargazing is not hindered by the light pollution common to most cities.

The best time for observation is during the late autumn months of the Northern Hemisphere, when Cassiopeia passes the meridian at midnight, but given its circumpolar nature in many northern localities, it is visible to many of the world's inhabitants throughout the year.  === Angular analysis === With the advances in optical interferometry in the 1990s, α Cassiopeiae's angular diameter was measured in 1998 at various wavelengths ranging from 500 to 850 nm. The result was a limb darkened angular measurement of 5.62 ± 0.06 milliarcseconds (mas),<ref name="HAJIAN">{{cite journal | title=Direct Confirmation of Stellar Limb Darkening with the Navy Prototype Optical Interferometer | display-authors=1 | last1=Hajian | first1=Arsen R. | last2=Armstrong | first2=J. T. | last3=Hummel | first3=C. A. | last4=Benson | first4=J. A. | journal=The Astrophysical Journal | date=March 1998 | volume=496 | issue=1 | pages=484 | doi=10.1086/305388 | bibcode=1998ApJ...496..484H| doi-access=free }}</ref> a diameter which equates to roughly 0.393 AU or {{Solar radius|link=y|42.3}}, assuming a parallax of 14.29 mas.<ref name="NOTERADIUS group=note">To determine α Cassiopeiae's ''average radius'' in terms of solar units, the calculations begin with the formula for angular diameter as follows:

:<math>\begin{smallmatrix} {\delta} = \frac{d_S}{D_S}\end{smallmatrix}</math>

where '''<math>{\delta}</math>''' equals the angular diameter of α Cassiopeiae in arcseconds, '''<math>{d_S}</math>''' the star's '''d'''iameter in AU, and '''<math>{D_S}</math>''' the '''D'''istance from Earth in parsecs. If one knows the angular diameter and the Distance, then one can solve for '''<math>{d_S}</math>''' as follows:

:<math>\begin{smallmatrix}d_S = \delta \cdot D_S = {0.00562} \cdot 70.0 = 0.393 AU\end{smallmatrix}</math>

To obtain α Cassiopeiae's radius:

:<math>\begin{smallmatrix}R_S = {\left ( {\frac {d_S}{2}} \right )} = {\left ( {\frac {0.393}{2}} \right )} = 0.197 AU\end{smallmatrix}</math>

To convert 0.197 AU into Solar units, the math is straightforward. Since 1 AU = 149,597,871 km and the mean diameter of the Sun = 1,392,000 km (hence a mean radius of 696,000 km), the calculation is as follows:

:<math>\begin{smallmatrix}d_S = {\left ( 0.197 AU \right )} {\left ( {\frac {149,597,871 km}{696,000 km}} \right )} = 42.31 R_{\odot} (rounded)\end{smallmatrix}</math>.</ref> With the planet Mercury orbiting the Sun at approximately 0.4 AU, α Cassiopeiae's photosphere extends to roughly half the mercurial orbit.

== Properties == thumb|left|upright=1.1|Cassiopeia starfield showing α Cas, the orange giant, in relation to the other stars in the constellation α Cassiopeiae is a red giant star whose spectral classification is K0-IIIa, notably cooler than the Sun.<ref name=perkins/> However, because it is nearing the final stages of its evolution, the photosphere has expanded substantially, yielding a bolometric luminosity that is approximately {{Solar luminosity|link=y|800}}. It is considered 98% likely to be a horizontal branch star fusing helium in its core.<ref name=reffert2015/>

According to ''Hipparcos'', the New Reduction (van Leeuwen, 2007), the estimated distance to the star is about 70 parsecs or 228 light-years.<ref name="LEEUWEN"/> Like all giant stars, α Cassiopeiae rotates slowly with an approximate velocity of {{val|6.7|u=km/s}}<ref name=hekker2007/>—a speed which takes the star approximately 102 days to make one complete revolution on its axis.{{cn|date=October 2020}}

[[File:Mercatur Cassiopeia.jpg|thumb|right|upright=0.8|Illustration from Gerardus Mercator showing α Cassiopeiae near the heart of the celestial Queen<ref name="HARVARD"> {{cite web |title=Cassiopeia — The Queen |publisher=The Mercator Globes at Harvard Map Collection |last=Mercator|first=Gerard |url=http://hcl.harvard.edu/libraries/maps/exhibits/mercator/main.html |access-date=2011-01-02 |archive-url=https://web.archive.org/web/20120817121654/http://hcl.harvard.edu/libraries/maps/exhibits/mercator/main.html |archive-date=2012-08-17 |url-status=dead }} </ref>]] α Cassiopeiae has been sometimes classified as a variable star, but no variability has been detected since the 19th century.<ref name="kaler">{{cite web |title=SHEDAR (Alpha Cassiopeiae) |publisher=University of Illinois |last=Kaler|first=James (Jim) B. |url=http://stars.astro.illinois.edu/sow/shedar.html |access-date=2010-02-22| archive-url= https://web.archive.org/web/20100327123048/http://stars.astro.illinois.edu/sow/shedar.html| archive-date= 27 March 2010 | url-status= live}}</ref> Also, three companions to the star have been listed in the Washington Double Star Catalog, but it seems that all of them are just distant line-of-sight optical components.<ref>{{cite DR2|418551988998944512}}</ref><ref>{{cite DR2|418551920283639296}}</ref><ref>{{cite DR2|418552366959945472}}</ref>

α Cassiopeiae is thought to be around 100 to 200 million years old, having spent much of that time as a blue-white B-type main-sequence star.<ref name="kaler"/>

== Depiction == In 1551, Gerardus Mercator, a Flemish cartographer, produced a celestial globe portraying the 48 traditional Ptolemaic constellations in addition to two others, Coma Berenices and Antinous.<ref name="HARVARD"/> On this globe, he represents Cassiopeia as the Queen of Ethiopia, punished for her boasting by being chained to a chair hanging upside-down. α Cassiopeiae is found near her left breast, reflecting its Arabic etymological origin. {{Clear}}

== References == {{Reflist|colwidth=25em}}

==External links== *Harvard Map Collection [https://web.archive.org/web/20120817121654/http://hcl.harvard.edu/libraries/maps/exhibits/mercator/main.html The Mercator Globes] *''The Internet Encyclopedia of Science'': [http://www.daviddarling.info/encyclopedia/S/Shedar.html Shedar (Alpha Cassiopeiae)]

{{Stars of Cassiopeia}} {{Sky|00|40|30.5|+|56|32|14.5|100000000}}  Category:K-type giants Category:Suspected variables Category:Horizontal-branch stars  Category:Cassiopeia (constellation) Cassiopeiae, Alpha 0168 Category:Durchmusterung objects Cassiopeiae, 18 003712 003179 Schedar Category:Lucidae Category:Brightest stars