View source for Astronomy:Cassiopeia (constellation)

{{Short description|Constellation in the northern celestial hemisphere}}
{{Infobox constellation
| name = Cassiopeia
| abbreviation = Cas
| genitive = Cassiopeiae
| symbolism = the Seated [[Social:Queen regnant|Queen]]
| RA = {{RA|22|57|04.5897}}–{{RA|03|41|14.0997}}<ref name=boundary/>
| dec= {{dec|77.6923447}}–{{dec|48.6632690}}<ref name=boundary/>
| family = Perseus
| areatotal = 598
| arearank = 25th
| numbermainstars = 5
| numberbfstars = 53
| numberstarsplanets = 14
| numberbrightstars = 4
| numbernearbystars = 7
| brighteststarname = [[Astronomy:Alpha Cassiopeiae|α Cas]] (Schedar){{efn|1=[[Astronomy:Gamma Cassiopeiae|γ Cas]] is variable and occasionally brighter than α.}}
| starmagnitude = 2.24
| neareststarname = [[Astronomy:Eta Cassiopeiae|η Cas]] (Achird)
| stardistancely = 19.42
| stardistancepc = 5.95
| numbermessierobjects = 2
| meteorshowers = [[Astronomy:Perseids|Perseids]]
| bordering = [[Astronomy:Camelopardalis|Camelopardalis]]<br />[[Astronomy:Cepheus (constellation)|Cepheus]]<br /> [[Astronomy:Lacerta|Lacerta]]<br /> [[Astronomy:Andromeda (constellation)|Andromeda]]<br /> [[Astronomy:Perseus (constellation)|Perseus]]
| latmax = [[Earth:North Pole|90]]
| latmin = 20
| month = November
| notes=}}
'''Cassiopeia''' ({{audio|Cassiopeia (spoken word).ogg|listen| help=no}}) is a [[Astronomy:Constellation|constellation]] and [[Astronomy:Asterism|asterism]] in the northern sky named after the vain queen Cassiopeia, mother of Andromeda, in [[Religion:Greek mythology|Greek mythology]], who boasted about her unrivaled beauty. Cassiopeia was one of the 48 constellations listed by the 2nd-century Greek astronomer [[Biography:Ptolemy|Ptolemy]], and it remains one of the 88 modern constellations today. It is easily recognizable due to its distinctive 'W' shape, formed by five bright stars.

Cassiopeia is located in the northern sky and from latitudes above 34°N it is visible year-round.  In the (sub)tropics it can be seen at its clearest from September to early November, and at low southern, tropical, latitudes of less than 25°S it can be seen, seasonally, low in the North.

At magnitude 2.2, [[Astronomy:Alpha Cassiopeiae|Alpha Cassiopeiae]], or Schedar, is generally the brightest star in Cassiopeia, though it is occasionally outshone by the [[Astronomy:Variable star|variable]] [[Astronomy:Gamma Cassiopeiae|Gamma Cassiopeiae]], which has reached magnitude 1.6. The constellation hosts some of the most luminous stars known, including the yellow hypergiants [[Astronomy:Rho Cassiopeiae|Rho Cassiopeiae]] and [[Astronomy:V509 Cassiopeiae|V509 Cassiopeiae]] and white hypergiant [[Astronomy:6 Cassiopeiae|6 Cassiopeiae]]. In 1572, [[Astronomy:SN 1572|Tycho Brahe's supernova]] flared brightly in Cassiopeia.<ref name=EB1911>{{cite EB1911 |wstitle=Cassiopeia |volume=5 |page=460}}</ref> [[Astronomy:Cassiopeia A|Cassiopeia A]] is a [[Astronomy:Supernova remnant|supernova remnant]] and the brightest extrasolar [[Astronomy:Astronomical radio source|radio source]] in the sky at frequencies above 1&nbsp;GHz. Fourteen star systems have been found to have [[Astronomy:Exoplanet|exoplanet]]s, one of which—[[Astronomy:HD 219134|HD 219134]]—is thought to host six planets. A rich section of the [[Astronomy:Milky Way|Milky Way]] runs through Cassiopeia, containing a number of [[Astronomy:Open cluster|open cluster]]s, young luminous galactic disc stars, and [[Astronomy:Nebula|nebula]]e. [[Astronomy:IC 10|IC 10]] is an irregular galaxy that is the closest known [[Astronomy:Starburst galaxy|starburst galaxy]] and the only one in the Local Group of galaxies.

== Mythology ==
[[File:Sidney Hall - Urania's Mirror - Cassiopeia (image right side up).jpg|thumb|left|upright=0.8|Cassiopeia in her chair, as depicted in ''[[Astronomy:Urania's Mirror|Urania's Mirror]]'']]
The constellation is named after Cassiopeia, the queen of [[Place:Aethiopia|Aethiopia]]. Cassiopeia was the wife of King Cepheus of Aethiopia<ref name=EB1911/> and mother of Princess Andromeda. Cepheus and Cassiopeia were placed next to each other among the stars, along with Andromeda. She was placed in the sky as a punishment after enraging [[Religion:Poseidon|Poseidon]] with the boast that her daughter Andromeda was more beautiful than the [[Unsolved:Nereid|Nereid]]s or, alternatively, that she herself was more beautiful than the sea nymphs.<ref>{{cite book|first=P.K. |last=Chen|title= A Constellation Album: Stars and Mythology of the Night Sky|page= 82 |year=2007|isbn= 9781931559386}}</ref> She was forced to wheel around the north celestial pole on her throne, spending half of her time clinging to it so she does not fall off, and Poseidon decreed that Andromeda should be bound to a rock as prey for the monster [[Astronomy:Cetus|Cetus]]. Andromeda was then rescued by the [[Social:Perseus|hero Perseus]], whom she later married.<ref name="staal">{{Harvnb|Staal|1988|pp=14–18}}</ref><ref name="chen">{{Harvnb|Chen|2007|pp=82–83}}</ref>

Cassiopeia has been variously portrayed throughout her history as a constellation. In Persia, she was drawn by al-Sufi as a queen holding a staff with a crescent moon in her right hand, wearing a crown, as well as a two-humped camel. In France, she was portrayed as having a marble throne and a palm leaf in her left hand, holding her robe in her right hand. This depiction is from Augustin Royer's 1679 atlas.<ref name="staal"/>

In [[Astronomy:Chinese astronomy|Chinese astronomy]], the stars forming the constellation Cassiopeia are found among three areas: the [[Astronomy:Purple Forbidden enclosure|Purple Forbidden enclosure]] (紫微垣, ''Zǐ Wēi Yuán''), the [[Astronomy:Black Tortoise|Black Tortoise of the North]] (北方玄武, ''Běi Fāng Xuán Wǔ''), and the White Tiger of the West (西方白虎, ''Xī Fāng Bái Hǔ'').

The Chinese astronomers saw several figures in what is modern-day Cassiopeia. Kappa, Eta, and Mu Cassiopeiae formed a constellation called the Bridge of the Kings; when seen along with Alpha and Beta Cassiopeiae, they formed the great chariot ''Wang-Liang''. The charioteer's whip was represented by Gamma Cassiopeiae, sometimes called "Tsih", the Chinese word for "whip".<ref name="staal"/>

In [[Religion:Hindu mythology|Hindu Mythology]], Cassiopeia was associated with the mythological figure Sharmishtha – the daughter of the great Devil (Daitya) King Vrishparva and a friend to Devayani (Andromeda).

In Welsh Mythology ''Llys Dôn'' (literally "The Court of Dôn") is the traditional [[Social:Welsh language|Welsh]] name for the constellation. At least three of Dôn's children also have astronomical associations: Caer Gwydion ("The fortress of Gwydion") is the traditional Welsh name for the [[Astronomy:Milky Way|Milky Way]], and Caer Arianrhod ("The Fortress of Arianrhod") being the constellation of [[Astronomy:Corona Borealis|Corona Borealis]].<ref>{{Cite book | url=https://books.google.com/books?id=nyjDAgAAQBAJ&pg=PT169 |title = Celtic Myth and Legend|isbn = 978-0-486-12209-0 | publisher=Courier Corporation |last1 = Squire|first1 = Charles|date = 2013}}</ref>

In the 17th century, various Biblical figures were depicted in the stars of Cassiopeia. These included [[Religion:Bathsheba|Bathsheba]], Solomon's mother; Deborah, an Old Testament prophet; and Mary Magdalene, a follower of [[Biography:Jesus|Jesus]].<ref name="staal"/>

A figure called the "Tinted Hand" also appeared in the stars of Cassiopeia in some Arab atlases. This is variously said to represent a woman's hand dyed red with henna, as well as the bloodied hand of [[Biography:Muhammad|Muhammad]]'s daughter Fatima. The hand is made up of the stars [[Astronomy:Alpha Cassiopeiae|α Cas]], [[Astronomy:Beta Cassiopeiae|β Cas]], [[Astronomy:Gamma Cassiopeiae|γ Cas]], [[Astronomy:Delta Cassiopeiae|δ Cas]], [[Astronomy:Epsilon Cassiopeiae|ε Cas]], and [[Astronomy:Eta Cassiopeiae|η Cas]]. The arm is made up of the stars [[Astronomy:Alpha Persei|α Per]], [[Astronomy:Gamma Persei|γ Per]], [[Astronomy:Delta Persei|δ Per]], [[Astronomy:Epsilon Persei|ε Per]], [[Astronomy:Eta Persei|η Per]], and [[Astronomy:Nu Persei|ν Per]].<ref name="staal"/>

Another Arab constellation that incorporated the stars of Cassiopeia was the Camel. Its head was composed of Lambda, Kappa, Iota, and Phi Andromedae; its hump was Beta Cassiopeiae; its body was the rest of Cassiopeia, and the legs were composed of stars in Perseus and Andromeda.<ref name="staal"/>

Other cultures see a hand or moose antlers in the pattern.<ref>{{cite book |last=Ptak |first=Robert |title=Sky Stories Ancient and Modern |location=New York |publisher=Nova Science Publishers |year=1998 |page=104}}</ref> These include the [[Place:Sámi people|Sámi]], for whom the W of Cassiopeia forms an elk antler. The Chukchi of Siberia similarly saw the five main stars as five reindeer stags.<ref name="staal"/>

The people of the Marshall Islands saw Cassiopeia as part of a great porpoise constellation. The main stars of Cassiopeia make its tail, Andromeda and [[Astronomy:Triangulum|Triangulum]] form its body, and [[Astronomy:Aries (constellation)|Aries]] makes its head.<ref name="staal"/> In Hawaii, Alpha, Beta, and Gamma Cassiopeiae were named. Alpha Cassiopeiae was called ''Poloahilani'', Beta Cassiopeiae was called ''Polula'', and Gamma Cassiopeiae was called ''Mulehu''. The people of Pukapuka saw the figure of Cassiopeia as a distinct constellation called ''Na Taki-tolu-a-Mataliki''.<ref>{{cite book
  | last = Makemson
  | first = Maud Worcester
  | year = 1941
  | publisher = Yale University Press
  | title = The Morning Star Rises: an account of Polynesian astronomy
  | page = 281
  | bibcode = 1941msra.book.....M
 }}</ref>

== Characteristics ==
[[File:Cassieopeia.jpg|thumb|left|upright=0.8|Cassiopeia in the night sky]]
[[File:Cassiopeia.4m-10m.webm|thumb|right|Cassiopeia, animation of all stars from 4th to 10th magnitude]] Cassiopeia had a supernova, Cassiopeia A, [[Astronomy:SN 1572|SN 1572]].

Covering 598.4 square degrees and hence 1.451% of the sky, Cassiopeia ranks [[Astronomy:88 modern constellations by area|25th]] of the 88 constellations in area.<ref name=tirionconst>{{cite web| url=http://www.ianridpath.com/constellations1.html | title=Constellations: Andromeda–Indus | work= Star Tales |author=Ian Ridpath|publisher=self-published | access-date= 2 December 2016| }}</ref> It is bordered by Cepheus to the north and west, Andromeda to the south and west, Perseus to the southeast and Camelopardalis to the east, and also shares a short border with Lacerta to the west.

The three-letter abbreviation for the constellation, as adopted by the [[Organization:International Astronomical Union|International Astronomical Union]] in 1922, is "Cas".<ref name="pa30_469">{{cite journal | last=Russell | first=Henry Norris | title=The New International Symbols for the Constellations | journal=Popular Astronomy | volume=30 | page=469 | bibcode=1922PA.....30..469R | year=1922 }}</ref> The official constellation boundaries, as set by Belgian astronomer [[Biography:Eugène Joseph Delporte|Eugène Delporte]] in 1930,{{efn|1=Delporte had proposed standardising the constellation boundaries to the International Astronomical Union, who had agreed and gave him the lead role<ref name=tirionconstbnd>{{cite web| url=http://www.ianridpath.com/boundaries.html | title=Constellation boundaries: How the modern constellation outlines came to be| work= Star Tales |author=Ridpath, Ian |author-link=Ian Ridpath|publisher=self-published | access-date= 1 June 2016}}</ref>}} are defined by a polygon of 30 segments. In the [[Astronomy:Equatorial coordinate system|equatorial coordinate system]], the [[Right ascension|right ascension]] coordinates of these borders lie between {{RA|00|27|03}} and {{RA|23|41|06}}, while the [[Declination|declination]] coordinates are between 77.69° and 46.68°.<ref name="boundary">{{Cite journal | title=Cassiopeia, Constellation Boundary | journal=The Constellations | publisher=International Astronomical Union | url=https://www.iau.org/public/themes/constellations/#cas | access-date=2 December 2016}}</ref>  Its position in the Northern Celestial Hemisphere means that the whole constellation is visible to observers north of 12°S.<ref name=tirionconst/>{{efn|1=While parts of the constellation technically rise above the horizon to observers between the latitudes of 12°S and 43°S, stars within a few degrees of the horizon are to all intents and purposes unobservable.<ref name=tirionconst/>}} High in the northern sky, it is circumpolar (that is, it never sets in the night sky) to viewers in the British Isles, Canada and the northern United States.<ref name=arnold>{{cite book |author1=Arnold, H.J.P |author2=Doherty, Paul |author3=Moore, Patrick  |title=The Photographic Atlas of the Stars |publisher=CRC Press |location=Boca Raton, Florida |date=1999 |page=20 |isbn=978-0-7503-0654-6 |url=https://books.google.com/books?id=YjcvJUfnWBAC&pg=PA20}}</ref>

== Features ==
=== Stars ===
{{Main|Astronomy:List of stars in Cassiopeia}}
[[File:CassiopeiaCC.jpg|thumb|left|upright|The constellation Cassiopeia as it can be seen by the naked eye from a northern location]]
The German cartographer Johann Bayer used the Greek letters Alpha through Omega, and then A and B, to label the most prominent 26 stars in the constellation. Upsilon was later found to be two stars and labelled Upsilon<sup>1</sup> and Upsilon<sup>2</sup> by John Flamsteed. B Cassiopeiae was in fact the supernova known as [[Astronomy:SN 1572|Tycho's Supernova]].<ref name=wagman>{{cite book | last = Wagman  | first = Morton  | date = 2003  | title = Lost Stars: Lost, Missing and Troublesome Stars from the Catalogues of Johannes Bayer, Nicholas Louis de Lacaille, John Flamsteed, and Sundry Others  | publisher = The McDonald & Woodward Publishing Company  | location = Blacksburg, Virginia  | isbn = 978-0-939923-78-6 |pages=91–92}}</ref> Within the constellation's borders, there are 157 stars brighter than or equal to [[Astronomy:Apparent magnitude|apparent magnitude]]&nbsp;6.5.{{efn|1=Objects of magnitude 6.5 are among the faintest visible to the unaided eye in suburban-rural transition night skies.<ref>{{cite web|url=http://www.skyandtelescope.com/resources/darksky/3304011.html?page=1&c=y|title=The Bortle Dark-Sky Scale|last=Bortle|first=John E.|date=February 2001|work=Sky & Telescope|publisher=Sky Publishing Corporation|access-date=6 June 2015}}</ref>}}<ref name=tirionconst/>

==== 'W' asterism ====
The five brightest stars of Cassiopeia – Alpha, Beta, Gamma, Delta, and Epsilon Cassiopeiae – form the characteristic W-shaped [[Astronomy:Asterism|asterism]].<ref name=arnold/> All five are prominent naked eye stars, three are noticeably [[Astronomy:Variable star|variable]], and a fourth is a suspected low amplitude variable. The asterism is oriented as a W when below [[Astronomy:Polaris|Polaris]] during northern spring and summer nights. In northern winter, and when seen from southern latitudes, it is "above" Polaris (i.e. closer to the [[Zenith|zenith]]) and the W appears inverted.

[[Astronomy:Alpha Cassiopeiae|Alpha Cassiopeiae]], traditionally called Schedar (from the Arabic ''Al Sadr'', "the breast"), is a four-star system. The primary dominates, an orange-hued [[Astronomy:Giant star|giant]] of magnitude 2.2, 228 ± 2 light-years from Earth.<ref name="vanLeeuwen2007">{{cite journal | first=F. | last=van Leeuwen | title=Validation of the New Hipparcos Reduction | journal=Astronomy and Astrophysics | volume=474 | issue=2 | pages=653–64 | date=2007 | bibcode=2007A&A...474..653V | doi=10.1051/0004-6361:20078357 | arxiv=0708.1752| s2cid=18759600 }}</ref> With a [[Astronomy:Luminosity|luminosity]] of around 771 times that of the Sun, it has swollen and cooled after exhausting its core hydrogen over its 100 to 200 million-year lifespan, spending much of it as a blue-white [[Astronomy:B-type main-sequence star|B-type main-sequence star]].<ref name="kaler">{{cite web   |title=SHEDAR (Alpha Cassiopeiae)   |publisher=University of Illinois   |author=Professor James B. (Jim) Kaler   |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> Magnitude 8.9 yellow dwarf companion (B) is widely separated; companions (C and D) are closer and magnitudes 13 and 14 respectively.<ref name=wds>{{cite journal|bibcode=2001AJ....122.3466M|title=The 2001 US Naval Observatory Double Star CD-ROM. I. The Washington Double Star Catalog|journal=The Astronomical Journal|volume=122|issue=6|page=3466|last1=Mason|first1=Brian D.|last2=Wycoff|first2=Gary L.|last3=Hartkopf|first3=William I.|last4=Douglass|first4=Geoffrey G.|last5=Worley|first5=Charles E.|year=2001|doi=10.1086/323920|doi-access=free}}</ref>

[[Astronomy:Beta Cassiopeiae|Beta Cassiopeiae]], or Caph (meaning "hand"), is a white-hued star of magnitude 2.3, 54.7 ± 0.3 light-years from Earth.<ref name="vanLeeuwen2007"/> Around 1.2 billion years old, it has used up its core hydrogen and begun expanding and cooling off the main sequence. It is around 1.9 times as massive as the Sun, and around 21.3 times as luminous. Rotating at about 92% of its [[Astronomy:Stellar rotation|critical speed]], Caph completes a full rotation every 1.12&nbsp;days. This is giving the star an oblate spheroid shape with an equatorial bulge that is 24% larger than the polar radius.<ref name=apj732_2>{{cite journal | last1=Che | first1=X. | last2=Monnier | first2=J. D. | last3=Zhao | first3=M. | last4=Pedretti | first4=E. | last5=Thureau | first5=N. | last6=Mérand | first6=A. | last7=ten Brummelaar | first7=T. | last8=McAlister | first8=H. | last9=Ridgway | first9=S. T. | title=Colder and Hotter: Interferometric Imaging of β Cassiopeiae and α Leonis | journal=The Astrophysical Journal | volume=732 | issue=2 | page=68 |date=2011 | doi=10.1088/0004-637X/732/2/68 | bibcode=2011ApJ...732...68C |arxiv = 1105.0740 | s2cid=14330106 }}</ref><!-- cites previous 4 sentences --> It is a [[Astronomy:Delta Scuti variable|Delta Scuti variable]] with a small amplitude and period of 2.5 hours.<ref name=kalerbeta>{{cite web | last1=Kaler | first1=James B. (Jim) | url=http://stars.astro.illinois.edu/sow/caph.html | title=Caph | work=Stars | publisher=University of Illinois | access-date=5 December 2016}}</ref>

[[Astronomy:Gamma Cassiopeiae|Gamma Cassiopeiae]] is the prototype [[Astronomy:Gamma Cassiopeiae variable|Gamma Cassiopeiae variable star]], a type of variable star that has a variable disc of material flung off by the high rotation rate of the star. Gamma Cassiopeiae has a minimum magnitude of 3.0 and a maximum magnitude of 1.6, but is generally near magnitude 2.2, with unpredictable fades and brightenings. It is a spectroscopic binary, with an orbital period of 203.59 days and a companion with a calculated mass about the same as the Sun. However, no direct evidence of this companion has been found, leading to speculation that it might be a white dwarf or other degenerate star.<ref>{{cite journal | title=Properties and nature of Be stars. XX. Binary nature and orbital elements of gamma Cas |author1=Harmanec, P. |author2=Habuda, P. |author3=Štefl, S. |author4=Hadrava, P. |author5=Korčáková, D. |author6=Koubský, P. |author7=Krtička, J. |author8=Kubát, J. |author9=Škoda, P. |author10=Šlechta, M. |author11=Wolf, M. | journal =Astronomy and Astrophysics| volume=364| pages=L85–L88 |year=2000| bibcode=2000A&A...364L..85H|arxiv = astro-ph/0011516 }}</ref>  It is 550 ± 10 light-years from Earth.

[[Astronomy:Delta Cassiopeiae|Delta Cassiopeiae]], also known as Ruchbah or Rukbat, meaning "knee," is a possible [[Astronomy:Algol variable|Algol-type]] [[Astronomy:Eclipsing binary|eclipsing binary]] star with a maximum brightness of magnitude 2.7. It has been reported to show eclipses of less than 0.1 magnitudes with a period of 2 years and 1 month.,{{sfn|Ridpath|Tirion|2001|pp=106–108}} but this has never been confirmed.  It is 99.4 ± 0.4 light-years from Earth.<ref name="vanLeeuwen2007"/>

[[Astronomy:Epsilon Cassiopeiae|Epsilon Cassiopeiae]] has an apparent magnitude of 3.3. Located 410 ± 20 light-years from Earth,<ref name="vanLeeuwen2007"/> it is a hot blue-white star of spectral type B3 III with a surface temperature of 15,680 K. It is 6.5 times as massive and 4.2 times as wide as the Sun, and belongs to a class of stars known as [[Astronomy:Be star|Be star]]s—rapidly spinning stars that throw off a [[Astronomy:Shell star|ring or shell]] of matter.<ref name=catanzaro13>{{cite journal|last=Catanzaro|first=G.|date=2013|title=Spectroscopic atlas of Hα and Hβ in a sample of northern Be stars|journal=Astronomy & Astrophysics|volume=550|issue=A79|page=18|doi=10.1051/0004-6361/201220357 | bibcode=2013A&A...550A..79C|arxiv = 1212.6608 }}</ref>

==== Fainter stars ====
[[File:Kappa Cassiopeiae.jpg|thumb|right|upright=1.0|Kappa Cassiopeiae and its bow shock. [[Astronomy:Spitzer Space Telescope|Spitzer]] infrared image (NASA/JPL-Caltech)]]
The next seven brightest stars in Cassiopeia are also all confirmed or suspected variable stars, including [[Astronomy:50 Cassiopeiae|50 Cassiopeiae]] which was not given a Greek letter by Bayer and is a suspected variable with a very small amplitude. [[Astronomy:Zeta Cassiopeiae|Zeta Cassiopeiae]] (Fulu<ref name="IAU-LSN">{{cite web | url=https://www.iau.org/public/themes/naming_stars/ | title=Naming Stars |publisher=IAU.org |access-date=30 July 2018}}</ref>) is a suspected [[Astronomy:Slowly pulsating B-type star|slowly pulsating B-type star]]. [[Astronomy:Eta Cassiopeiae|Eta Cassiopeiae]] (Achird<ref name="IAU-LSN"/>) is a spectroscopic binary star with a period of 480 years, and a suspected [[Astronomy:RS Canum Venaticorum variable|RS Canum Venaticorum variable]]. The primary is a yellow-hued star of magnitude 3.5 and the secondary is a red-hued star of magnitude 7.5. The system is 19 light-years from Earth. [[Astronomy:Kappa Cassiopeiae|Kappa Cassiopeiae]] is a [[Astronomy:Blue supergiant|blue supergiant]] of spectral type BC0.7Ia that is some 302,000 times as luminous as the Sun and has 33 times its diameter.<ref name=searle>{{cite journal|bibcode=2008A&A...481..777S|arxiv=0801.4289|title=Quantitative studies of the optical and UV spectra of Galactic early B supergiants. I. Fundamental parameters|journal=Astronomy and Astrophysics|volume=481|issue=3|page=777|last1=Searle|first1=S. C.|last2=Prinja|first2=R. K.|last3=Massa|first3=D.|last4=Ryans|first4=R.|year=2008|doi=10.1051/0004-6361:20077125|s2cid=1552752}}</ref> It is a [[Astronomy:Runaway stars|runaway star]], moving at around 2.5 million mph relative to its neighbors (1,100 kilometers per second).<ref>{{cite web|last=Clavin|first=Whitney|title=The bow shock of Kappa Cassiopeiae, a massive, hot supergiant|date=21 February 2014|url=http://phys.org/news/2014-02-kappa-cassiopeiae-massive-hot-supergiant.html|publisher=Phys.org|access-date=6 December 2016}}</ref> Its magnetic field and wind of particles creates a visible [[Astronomy:Bow shock|bow shock]] 4 light-years ahead of it, colliding with the diffuse, and usually invisible, interstellar gas and dust. The dimensions of the bow shock are vast: around 12 light-years long and 1.8 light-years wide.<ref name=peri>{{cite journal|bibcode=2012A&A...538A.108P |title=E-BOSS: An Extensive stellar BOw Shock Survey. I. Methods and first catalogue |journal=Astronomy & Astrophysics |volume=538 |pages=A108 |last1=Peri |first1=C. S. |last2=Benaglia |first2=P. |last3=Brookes |first3=D. P. |last4=Stevens |first4=I. R. |last5=Isequilla |first5=N. L. |year=2012 |doi=10.1051/0004-6361/201118116 |arxiv = 1109.3689 |s2cid=62840857 }}</ref> [[Astronomy:Theta Cassiopeiae|Theta Cassiopeiae]], named Marfak, is a suspected variable star whose brightness changes by less than a tenth of a magnitude. [[Astronomy:Iota Cassiopeiae|Iota Cassiopeiae]] is a [[Astronomy:Triple star|triple star]] 142 light-years from Earth. The primary is a white-hued star of magnitude 4.5 and an [[Astronomy:Alpha2 Canum Venaticorum variable|α<sup>2</sup> Canum Venaticorum variable]], the secondary is a yellow-hued star of magnitude 6.9, and the tertiary is a star of magnitude 8.4. The primary and secondary are close together but the primary and tertiary are widely separated. [[Astronomy:Omicron Cassiopeiae|Omicron Cassiopeiae]] is a triple star and the primary is another γ Cassiopeiae variable.

[[Astronomy:Sigma Cassiopeiae|Sigma Cassiopeiae]] is a binary star 1500 light-years from Earth. It has a green-hued primary of magnitude 5.0 and a blue-hued secondary of magnitude 7.3. [[Astronomy:Psi Cassiopeiae|Psi Cassiopeiae]] is a triple star 193 light-years from Earth. The primary is an orange-hued giant star of magnitude 4.7 and the secondary is a close pair of stars that appears to be of magnitude 9.0.{{sfn|Ridpath|Tirion|2001|pp=106–108}}

[[Astronomy:Rho Cassiopeiae|Rho Cassiopeiae]] is a [[Astronomy:Semiregular variable star|semi-regular pulsating variable]] [[Astronomy:Yellow hypergiant|yellow hypergiant]], among the most luminous stars in the galaxy at approximately {{solar luminosity|500,000}}.<ref name=strothers12>{{cite journal | bibcode=2012ApJ...751..151S| title=Yellow Hypergiants Show Long Secondary Periods?| journal=The Astrophysical Journal| volume=751| issue=2| page=151| last1=Stothers| first1=Richard B.| year=2012| doi=10.1088/0004-637X/751/2/151| s2cid=121048201}}</ref> It has a minimum magnitude of 6.2 and a maximum magnitude of 4.1; its period is approximately 320 days. It has around 450 times the Sun's diameter and 17 times its mass, having begun life 45 times as massive as the Sun. Rho Cassiopeiae is about 10,000 light-years from Earth.  Cassiopeia includes [[Astronomy:V509 Cassiopeiae|V509 Cassiopeiae]], a second example of the extremely rare yellow hypergiants, which is around 400,000 times as luminous as the Sun and 14 times as massive,<ref name=strothers12/> as well as [[Astronomy:6 Cassiopeiae|6 Cassiopeiae]] which is a hotter white [[Astronomy:Hypergiant|hypergiant]].  It also hosts the red supergiant [[Astronomy:PZ Cassiopeiae|PZ Cassiopeiae]], which is one of the [[Astronomy:List of largest stars|largest known stars]] with an estimate of {{solar radius|1,190–1,940}} and is also a semiregular variable.<ref name=levesque2005>{{cite journal |title=The Effective Temperature Scale of Galactic Red Supergiants: Cool, but Not As Cool As We Thought |last1=Levesque|first1=Emily M.|last2=Massey|first2=Philip|last3=Olsen|first3=K. A. G.|first4=Bertrand|last4=Plez|first5=Eric|last5=Josselin|first6=Andre|last6=Maeder|first7=Georges|last7=Meynet |journal=The Astrophysical Journal |volume=628 |issue=2 |date=August 2005 |pages=973–985 |doi=10.1086/430901 |bibcode=2005ApJ...628..973L|arxiv = astro-ph/0504337 |s2cid=15109583}}</ref> Between 240,000 and 270,000 times as luminous as the Sun, it is around 9,160 light-years distant from Earth.<ref name=Kusuno>{{Cite journal | last1 = Kusuno | first1 = K. | last2 = Asaki | first2 = Y. | last3 = Imai | first3 = H. | last4 = Oyama | first4 = T. | title = Distance and Proper Motion Measurement of the Red Supergiant, Pz Cas, in Very Long Baseline Interferometry H2O Maser Astrometry | doi = 10.1088/0004-637X/774/2/107 | journal = The Astrophysical Journal | volume = 774 | issue = 2 | page = 107 | year = 2013 | bibcode = 2013ApJ...774..107K | arxiv=1308.3580 | s2cid = 118867155 }}</ref>

[[Astronomy:AO Cassiopeiae|AO Cassiopeiae]] is a [[Astronomy:Binary star|binary system]] composed of an O8 main sequence star and an O9.2 bright giant that respectively weigh anywhere between 20.30 and 57.75 times and 14.8 and 31.73 times the mass of the [[Astronomy:Sun|Sun]].<ref name=an331_4_349>{{cite journal | doi=10.1002/asna.200911355 | bibcode=2010AN....331..349H |arxiv = 1003.2335 | title=Masses and luminosities of O- and B-type stars and red supergiants | journal=Astronomische Nachrichten | volume=331 | issue=4 | page=349 | year=2010 | last1=Hohle | first1=M.M. | last2=Neuhäuser | first2=R. | last3=Schutz | first3=B.F. | s2cid=111387483 }}</ref> The two massive stars are so close to each other they distort each other into egg-shapes.<ref>{{cite book|title=Astronomy and Cosmogony|url=https://books.google.com/books?id=M988AAAAIAAJ&pg=PA125|publisher=CUP Archive|pages=125–|id=GGKEY:KFJRG3PWW14|year = 1928}}</ref>

[[Astronomy:SN 1572|Tycho Brahe's supernova]] was visible within Cassiopeia, and the star [[Astronomy:Tycho G|Tycho G]] is suspected of being the donor of the material that triggered that explosion.

=== Deep-sky objects ===
[[File:Potw1327a.tif|thumb|left|upright=1.0|Planetary nebula [[Astronomy:IC 289|IC 289]] is a cloud of ionised gas being pushed out into space by the remnants of the star's core]]
A rich section of the [[Astronomy:Milky Way|Milky Way]] runs through Cassiopeia, stretching from [[Astronomy:Perseus (constellation)|Perseus]] towards [[Astronomy:Cygnus (constellation)|Cygnus]], and it contains a number of [[Astronomy:Open cluster|open cluster]]s, young luminous galactic disc stars, and [[Astronomy:Nebula|nebula]]e.

The [[Astronomy:Heart Nebula|Heart Nebula]] and the Soul Nebula are two neighboring [[Astronomy:Emission nebula|emission nebula]]e about 7,500 light-years away.

Two Messier objects, [[Astronomy:Messier 52|M52]] (NGC 7654) and [[Astronomy:Messier 103|M103]] (NGC 581), are located in Cassiopeia; both are open clusters. M52, once described as a "kidney-shaped" cluster, contains approximately 100 stars and is 4600 light-years from Earth.<ref name=Wu2009>{{citation | display-authors=1
 | last1=Wu | first1=Zhen-Yu | last2=Zhou | first2=Xu
 | last3=Ma | first3=Jun | last4=Du | first4=Cui-Hua
 | title=The orbits of open clusters in the Galaxy
 | journal=[[Organization:Monthly Notices of the Royal Astronomical Society|Monthly Notices of the Royal Astronomical Society]]
 | volume=399 | issue=4 | pages=2146–2164 | date=November 2009
 | doi=10.1111/j.1365-2966.2009.15416.x | postscript=.
 | bibcode=2009MNRAS.399.2146W | arxiv=0909.3737 | s2cid=6066790 }}</ref> Its most prominent member is an orange-hued star of magnitude 8.0 near the cluster's edge. M103 is far poorer than M52, with only about 25 stars included. It is also more distant, between 8000 and 9500 light-years from Earth.<ref name="aaa349">
{{cite journal
|author=Sanner, J. |author2=Geffert, M. |author3=Brunzendorf, J. |author4=Schmoll, J.
|date=1999
|title=Photometric and kinematic studies of open star clusters. I. NGC 581 (M 103)
|journal=Astronomy and Astrophysics
|volume=349|pages=448–456
|bibcode=1999A&A...349..448S
|arxiv = astro-ph/9908059 }}</ref> Its most prominent member is actually a closer, superimposed double star; it consists of a 7th-magnitude primary and 10th-magnitude secondary.{{sfn|Ridpath|Tirion|2001|pp=106–108}}

The other prominent open clusters in Cassiopeia are [[Astronomy:NGC 457|NGC 457]] and [[Astronomy:NGC 663|NGC 663]], both of which have about 80 stars. NGC 457 is looser, and its brightest member is [[Astronomy:Phi Cassiopeiae|Phi Cassiopeiae]], a white-hued supergiant star of magnitude 5.0. However, it is uncertain whether Phi Cassiopeiae is part of the open cluster or not.<ref name=PhiCas>{{Cite journal | doi = 10.1088/0004-6256/144/3/86| title = B-Type Variables in the Young Open Cluster Ngc 457| year = 2012| last1 = Zhang | first1 = X. B.| last2 = Luo | first2 = C. Q.| last3 = Fu | first3 = J. N.| journal = The Astronomical Journal| volume = 144| issue = 3| pages = 86| bibcode = 2012AJ....144...86Z| s2cid = 250804951}}</ref> The stars of NGC 457, arrayed in chains, are approximately 10,000 light-years from Earth. NGC 663 is both closer, at 8200 light-years from Earth, and larger, at 0.25 degrees in diameter.{{sfn|Ridpath|Tirion|2001|pp=106–108}}

There are two [[Astronomy:Supernova remnant|supernova remnant]]s in Cassiopeia. The first, designated 3C 10 or just ''Tycho's Supernova Remnant'', is the aftermath of the supernova called Tycho's Star. It was observed in 1572 by [[Biography:Tycho Brahe|Tycho Brahe]] and now exists as a bright object in the [[Physics:Radio spectrum|radio spectrum]].{{sfn|Ridpath|Tirion|2001|pp=106–108}} Within the 'W' asterism formed by Cassiopeia's five major stars lies [[Astronomy:Cassiopeia A|Cassiopeia A]] (Cas A). It is the remnant of a [[Astronomy:Supernova|supernova]] that took place approximately 300 years ago (as observed now from Earth; it is 10,000 light-years away),<ref name="objects">{{cite book |title = 300 Astronomical Objects: A Visual Reference to the Universe |last1=Wilkins |first1=Jamie |last2=Dunn |first2 = Robert |publisher = Firefly Books |date = 2006 |edition = 1st |location=Buffalo, New York |isbn = 978-1-55407-175-3}}</ref> and has the distinction of being the strongest radio source observable outside the [[Astronomy:Solar System|Solar System]]. It was perhaps observed as a faint star in 1680 by John Flamsteed. It was also the subject of the first image returned by the Chandra X-Ray Observatory in the late 1990s. The shell of matter expelled from the star is moving at {{convert|4000|km|mi}} per second; it has a temperature of 30,000 [[Kelvin|kelvin]]s on average.<ref name="objects"/>

[[Astronomy:NGC 457|NGC 457]] is another open cluster in Cassiopeia, also called the E.T. Cluster, the Owl Cluster, and [[Astronomy:Caldwell catalogue|Caldwell]] 13. The cluster was discovered in 1787 by William Herschel. It has an overall magnitude of 6.4 and is approximately 10,000 light-years from Earth, lying in the Perseus arm of the [[Astronomy:Milky Way|Milky Way]]. However, its most prominent member, the [[Astronomy:Double star|double star]] [[Astronomy:Phi Cassiopeiae|Phi Cassiopeiae]], is far closer – between 1000 and 4000 light-years away. NGC 457 is fairly rich; it is a Shapley class e and Trumpler class I 3 r cluster. It is concentrated towards its center and detached from the star field. It contains more than 100 stars, which vary widely in brightness.{{sfn|Levy|2005|pp=92–93}}

Two members of the [[Astronomy:Local Group|Local Group]] of galaxies are in Cassiopeia. [[Astronomy:NGC 185|NGC 185]] is a magnitude 9.2 [[Astronomy:Elliptical galaxy|elliptical galaxy]] of type E0, 2 million light-years away. Slightly dimmer and more distant [[Astronomy:NGC 147|NGC 147]] is a magnitude 9.3 elliptical galaxy, like NGC 185 it is an elliptical of type E0; it is 2.3 million light-years from Earth. Though they do not appear in [[Astronomy:Andromeda (constellation)|Andromeda]], both [[Astronomy:Dwarf galaxy|dwarf galaxies]] are gravitationally bound to the far larger [[Astronomy:Andromeda Galaxy|Andromeda Galaxy]].{{sfn|Levy|2005|pp=180–181}}

[[Astronomy:IC 10|IC 10]] is an irregular galaxy that is the closest known [[Astronomy:Starburst galaxy|starburst galaxy]] and the only one in the Local Group of galaxies.<ref>{{cite journal | last1 =Nidever| first1= David L.| first2=  Trisha | last2 =Ashley| first3=  Colin T. | last3 =Slater| first4=  Jürgen | last4 =Ott| first5=  Megan | last5 =Johnson| first6=  Eric F. | last6 =Bell | first7= Snežana | last7 =Stanimirović | last8 =Putman| first8=  Mary| last9 = Majewski | first9= Steven R.| last10 = Simpson | first10= Caroline E. | last11 =Jütte | first11= Eva | first12= Tom A. | last12 =Oosterloo | first13= W. Butler | last13 =Burton | title=Evidence for an interaction in the nearest starbursting dwarf irregular galaxy IC 10 | journal= The Astrophysical Journal Letters | volume=779|issue= 2 |year=2013|page= L15|arxiv = 1310.7573 |bibcode = 2013ApJ...779L..15N |doi = 10.1088/2041-8205/779/2/L15 | s2cid= 119238691}}</ref>

Cassiopeia also contains part of the closest galaxy group to our Local Group, the IC 342/Maffei Group. The galaxies [[Astronomy:Maffei 1|Maffei 1]] and [[Astronomy:Maffei 2|Maffei 2]] are located just to the south of the Heart and Soul nebulae. As a result of this location in the Zone of Avoidance, both are surprisingly faint despite both being within 10 million light-years away (Maffei 2 is below the range of most amateur telescopes).<ref name="karachentsev2005">{{cite journal
  | author=I. D. Karachentsev
  | title=The Local Group and Other Neighboring Galaxy Groups
  | journal=Astronomical Journal
  | date=2005
  | volume=129
  | issue=1
  | pages=178–188
  | bibcode=2005AJ....129..178K | doi = 10.1086/426368
|arxiv = astro-ph/0410065 | s2cid=119385141
 }}</ref>

<gallery caption="The constellation Cassiopeia with star clusters" widths=420 heights=300 perrow=3>
Kassiopeia.labelled.P1023186.png|Cassiopeia with indication of [[Astronomy:Chi Persei|χ Persei (NGC 884)]] and h Persei (NGC 869) as well as the star clusters [[Astronomy:NGC 654|NGC 654]], [[Astronomy:NGC 663|NGC 663]], [[Astronomy:NGC 581|NGC 581]] (Messier 103), [[Astronomy:NGC 457|NGC 457]], [[Astronomy:NGC 225|NGC 225]], NGC 7788, [[Astronomy:NGC 7790|NGC 7790]], [[Astronomy:NGC 7789|NGC 7789]] and [[Astronomy:NGC 7654|NGC 7654]] (Messier 52).
</gallery>

=== Meteor shower ===
The December Phi Cassiopeiids are a recently discovered early December [[Astronomy:Meteor shower|meteor shower]] that [[Astronomy:Radiant (meteor shower)|radiates]] from Cassiopeia. Phi Cassiopeiids are very slow, with an entry velocity of approximately 16.7 kilometers per second. The shower's parent body is a Jupiter family comet, though its specific identity is unknown.<ref>{{cite journal |journal = Sky & Telescope |date = September 2012 |last = Jenniskens |first = Peter |page = 25 |title = Mapping Meteoroid Orbits: New Meteor Showers Discovered}}</ref>

== Namesakes ==
USS ''Cassiopeia'' (AK-75) was a United States Navy ''Crater''-class cargo ship named after the constellation.

In ''[[Software:Pokémon Scarlet and Violet|Pokémon Scarlet and Violet]]'', the villainous team, Team Star, is divided into five squads named after the brightest stars in the constellation: Segin Squad, [[Astronomy:Alpha Cassiopeiae|Schedar]] Squad, Ruchbah Squad, [[Astronomy:Gamma Cassiopeiae|Navi]] Squad, and Caph Squad. In addition, the character Penny's alias, Cassiopeia, is named after the constellation.

Cassiopeia is also the name of a song by London-based band Bears in Trees. Although the lyrics of the song mainly refer to the ancient Greek woman, the album cover shows the constellation.<ref>{{cite web |url=https://bearsintreesofficial.bandcamp.com/track/cassiopeia |title=Cassiopeia |website=Bandcamp |access-date=2023-09-01 }}</ref>

== See also ==
* Cassiopeia (Chinese astronomy)

== References ==
=== Explanatory notes ===
{{Notelist}}

=== Citations ===
{{Reflist|2}}

=== General and cited sources ===
* {{cite journal |last1=Krause |first1=O |last2=Rieke |first2=GH |last3=Birkmann |first3=SM |last4=Le Floc'h |first4=E |last5=Gordon |first5=KD |last6=Egami |first6=E |last7=Bieging |first7=J |last8=Hughes |first8=JP |last9=Young |first9=ET |last10=Hinz |first10=JL |last11=Quanz |first11=SP |last12=Hines |first12=DC | title=Infrared echoes near the supernova remnant Cassiopeia A | journal=Science | volume=308 | issue=5728 | year=2005 | pages=1604–6 | pmid=15947181 | doi=10.1126/science.1112035|arxiv = astro-ph/0506186 |bibcode = 2005Sci...308.1604K |s2cid=21908980 }}
* {{citation |title = Deep Sky Objects |last = Levy |first = David H. |publisher = Prometheus Books |year = 2005 |isbn = 1-59102-361-0 |url-access = registration |url = https://archive.org/details/deepskyobjects00davi }}
* {{citation |title = Stars and Planets Guide |last1 = Ridpath |first1 = Ian |last2 = Tirion |first2 = Wil |year = 2001 |publisher = Princeton University Press |isbn = 0-691-08913-2}}
* {{cite book |first1=Ian |last1=Ridpath |first2=Wil |last2=Tirion |year=2007 |title=Stars and Planets Guide |publisher=Collins |location=London |isbn=978-0-00-725120-9}}
* {{cite book
  | last = Staal
  | first = Julius D. W.
  | year = 1988
  | title = The New Patterns in the Sky: Myths and Legends of the Stars
  | publisher = The McDonald and Woodward Publishing Company
  | isbn = 978-0-939923-04-5
  }}

== External links ==
{{Commons and category|Cassiopeia|Cassiopeia (constellation)}}
* [http://www.allthesky.com/constellations/Cassiopeia/ The Deep Photographic Guide to the Constellations: Cassiopeia]
* [http://astrojan.nhely.hu/cassio.htm The clickable Cassiopeia]
* [http://www.ianridpath.com/startales/cassiopeia.html Star Tales – Cassiopeia]
* [https://iconographic.warburg.sas.ac.uk/category/vpc-taxonomy-017048 Warburg Institute Iconographic Database (ca 160 medieval and early modern images of Cassiopeia)]

{{Stars of Cassiopeia}}
{{Constellations}}
{{Sky|01|00|00|+|60|00|00|10}}

{{DEFAULTSORT:Cassiopeia (Constellation)}}
[[Category:Cassiopeia (constellation)| ]]
[[Category:Constellations]]
[[Category:Northern constellations]]
[[Category:Constellations listed by Ptolemy]]

{{Sourceattribution|Cassiopeia (constellation)}}