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Cassiopeia () is a
constellation A constellation is an area on the celestial sphere in which a group of visible stars forms Asterism (astronomy), a perceived pattern or outline, typically representing an animal, mythological subject, or inanimate object. The origins of the e ...
in the northern sky named after the vain queen Cassiopeia, mother of Andromeda, in
Greek mythology A major branch of classical mythology, Greek mythology is the body of myths originally told by the Ancient Greece, ancient Greeks, and a genre of Ancient Greek folklore. These stories concern the Cosmogony, origin and Cosmology#Metaphysical co ...
, who boasted about her unrivaled beauty. Cassiopeia was one of the 48 constellations listed by the 2nd-century Greek astronomer
Ptolemy Claudius Ptolemy (; grc-gre, Πτολεμαῖος, ; la, Claudius Ptolemaeus; AD) was a mathematician, astronomer, astrologer, geographer, and music theorist, who wrote about a dozen scientific treatises, three of which were of importanc ...
, 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, Alpha Cassiopeiae, or Schedar, is generally the brightest star in Cassiopeia, though it is occasionally outshone by the
variable Variable may refer to: * Variable (computer science), a symbolic name associated with a value and whose associated value may be changed * Variable (mathematics), a symbol that represents a quantity in a mathematical expression, as used in many ...
Gamma Cassiopeiae Gamma Cassiopeiae, Latinized from γ Cassiopeiae, is a bright star at the center of the distinctive "W" asterism in the northern circumpolar constellation of Cassiopeia. Although it is a fairly bright star with an apparent visual mag ...
, which has reached magnitude 1.6. The constellation hosts some of the most luminous stars known, including the yellow hypergiants
Rho Cassiopeiae Rho Cassiopeiae (; ρ Cas, ρ Cassiopeiae) is a yellow hypergiant star in the constellation Cassiopeia. It is about from Earth, yet can still be seen by the naked eye as it is over 300,000 times brighter than the Sun. On average it has a ...
and
V509 Cassiopeiae V509 Cassiopeiae (V509 Cas or HR 8752) is one of two yellow hypergiant stars found in the constellation Cassiopeia, which also contains Rho Cassiopeiae. HR 8752 is around 15,700 light-years from Earth. It has an apparent magnitude that ...
and white hypergiant
6 Cassiopeiae 6 Cassiopeiae (6 Cas) is a white hypergiant in the constellation Cassiopeia, and a small-amplitude variable star. System 6 Cassiopeiae A is a white A2.5 type hypergiant. It is about 25 times as massive as the Sun and 200,000 times a ...
. In 1572, Tycho Brahe's supernova flared brightly in Cassiopeia.
Cassiopeia A Cassiopeia A (Cas A) () is a supernova remnant (SNR) in the constellation Cassiopeia and the brightest extrasolar radio source in the sky at frequencies above 1 GHz. The supernova occurred approximately away within the Milky Way ...
is a
supernova remnant A supernova remnant (SNR) is the structure resulting from the explosion of a star in a supernova. The supernova remnant is bounded by an expanding shock wave, and consists of ejected material expanding from the explosion, and the interstellar mat ...
and the brightest extrasolar radio source in the sky at frequencies above 1 GHz. Fourteen star systems have been found to have
exoplanet An exoplanet or extrasolar planet is a planet outside the Solar System. The first possible evidence of an exoplanet was noted in 1917 but was not recognized as such. The first confirmation of detection occurred in 1992. A different planet, init ...
s, one of which—
HR 8832 HR, Hr or hr may refer to: Arts and media Film and television * ''H.R. Pufnstuf'', a children's television series from 1969 * ''HR'', a 2013 television drama starring Alicia Silverstone * HR, a criminal organisation in the American TV series ''P ...
—is thought to host seven planets. A rich section of the
Milky Way The Milky Way is the galaxy that includes our Solar System, with the name describing the galaxy's appearance from Earth: a hazy band of light seen in the night sky formed from stars that cannot be individually distinguished by the naked eye ...
runs through Cassiopeia, containing a number of
open cluster An open cluster is a type of star cluster made of up to a few thousand stars that were formed from the same giant molecular cloud and have roughly the same age. More than 1,100 open clusters have been discovered within the Milky Way galaxy, and ...
s, young luminous galactic disc stars, and
nebula A nebula ('cloud' or 'fog' in Latin; pl. nebulae, nebulæ or nebulas) is a distinct luminescent part of interstellar medium, which can consist of ionized, neutral or molecular hydrogen and also cosmic dust. Nebulae are often star-forming regio ...
e.
IC 10 IC 10 is an irregular galaxy in the constellation Cassiopeia. It was discovered by Lewis Swift in 1887 and in 1935 Nicholas Mayall became the first to suggest that the object is extragalactic. Edwin Hubble suspected it might belong to the Loc ...
is an irregular galaxy that is the closest known
starburst galaxy A starburst galaxy is one undergoing an exceptionally high rate of star formation, as compared to the long-term average rate of star formation in the galaxy or the star formation rate observed in most other galaxies. For example, the star formatio ...
and the only one in the Local Group of galaxies.


Mythology

The constellation is named after Cassiopeia, the queen of
Aethiopia Ancient Aethiopia, ( gr, Αἰθιοπία, Aithiopía; also known as Ethiopia) first appears as a geographical term in classical documents in reference to the upper Nile region of Sudan, as well as certain areas south of the Sahara desert. Its ...
. Cassiopeia was the wife of King Cepheus of Aethiopia 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
Poseidon Poseidon (; grc-gre, Ποσειδῶν) was one of the Twelve Olympians in ancient Greek religion and myth, god of the sea, storms, earthquakes and horses.Burkert 1985pp. 136–139 In pre-Olympian Bronze Age Greece, he was venerated as a ch ...
with the boast that her daughter Andromeda was more beautiful than the
Nereid In Greek mythology, the Nereids or Nereides ( ; grc, Νηρηΐδες, Nērēḯdes; , also Νημερτές) are sea nymphs (female spirits of sea waters), the 50 daughters of the 'Old Man of the Sea' Nereus and the Oceanids, Oceanid Doris ...
s or, alternatively, that she herself was more beautiful than the sea nymphs. She was forced to wheel around the
north celestial pole The north and south celestial poles are the two points in the sky where Earth's axis of rotation, indefinitely extended, intersects the celestial sphere. The north and south celestial poles appear permanently directly overhead to observers at ...
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
Cetus Cetus () is a constellation, sometimes called 'the whale' in English. The Cetus (mythology), Cetus was a sea monster in Greek mythology which both Perseus and Heracles needed to slay. Cetus is in the region of the sky that contains other water- ...
. Andromeda was then rescued by the hero Perseus, whom she later married. Cassiopeia has been variously portrayed throughout her history as a constellation. In Persia, she was drawn by
al-Sufi ʿAbd al-Rahman al-Sufi ( fa, عبدالرحمن صوفی; December 7, 903 – May 25, 986) was an iranianRobert Harry van Gent. Biography of al-Sūfī'. "The Persian astronomer Abū al-Husayn ‘Abd al-Rahmān ibn ‘Umar al-Sūfī was born in ...
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 Augustin Royer was a French architectKanas. N., (2007) ''Star Maps: History, Artistry, and Cartography'', Praxis, Chichester, p. 159. who lived in the time of Louis XIV. In 1679 he published a star map; in addition to the 48 constellations of P ...
's 1679 atlas. In
Chinese astronomy Astronomy in China has a long history stretching from the Shang dynasty, being refined over a period of more than 3,000 years. The ancient Chinese people have identified stars from 1300 BCE, as Chinese star names later categorized in the twe ...
, the stars forming the constellation Cassiopeia are found among three areas: the
Purple Forbidden enclosure The Purple Forbidden enclosure ( Zǐ wēi yuán) is one of the San Yuan ( Sān yuán) or Three Enclosures. Stars and constellations of this group lie near the north celestial pole and are visible all year from temperate latitudes in the Northern ...
(紫微垣, ''Zǐ Wēi Yuán''), the 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". In
Hindu Mythology Hindu mythology is the body of myths and literature attributed to, and espoused by, the adherents of the Hindu religion, found in Hindu texts such as the Vedic literature, epics like ''Mahabharata'' and ''Ramayana'', the Puranas, and reg ...
, 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 Welsh mythology (Welsh: ''Mytholeg Cymru'') consists of both folk traditions developed in Wales, and traditions developed by the Celtic Britons elsewhere before the end of the first millennium. As in most of the predominantly oral societies Cel ...
''Llys Dôn'' (literally "The Court of Dôn") is the traditional
Welsh Welsh may refer to: Related to Wales * Welsh, referring or related to Wales * Welsh language, a Brittonic Celtic language spoken in Wales * Welsh people People * Welsh (surname) * Sometimes used as a synonym for the ancient Britons (Celtic peop ...
name for the constellation. At least three of Dôn's children also have astronomical associations: Caer Gwydion ("The fortress of
Gwydion Gwydion fab Dôn () is a magician, hero and trickster of Welsh mythology, appearing most prominently in the Fourth Branch of the ''Mabinogi'', which focuses largely on his relationship with his young nephew, Lleu Llaw Gyffes. He also appears ...
") is the traditional Welsh name for the
Milky Way The Milky Way is the galaxy that includes our Solar System, with the name describing the galaxy's appearance from Earth: a hazy band of light seen in the night sky formed from stars that cannot be individually distinguished by the naked eye ...
, and Caer Arianrhod ("The Fortress of
Arianrhod Arianrhod () is a figure in Welsh mythology who plays her most important role in the Fourth Branch of the ''Mabinogi''. She is the daughter of Dôn and the sister of Gwydion and Gilfaethwy; the Welsh Triads give her father as Beli Mawr.Triad 35 ...
") being the constellation of
Corona Borealis Corona Borealis is a small constellation in the Northern Celestial Hemisphere. It is one of the 48 constellations listed by the 2nd-century astronomer Ptolemy, and remains one of the 88 modern constellations. Its brightest stars form a se ...
. In the 17th century, various
Biblical figures Names play a variety of roles in the Bible. They sometimes relate to the nominee's role in a biblical narrative, as in the case of Nabal, a foolish man whose name means "fool". Names in the Bible can represent human hopes, divine revelations, o ...
were depicted in the stars of Cassiopeia. These included Bathsheba, Solomon's mother;
Deborah According to the Book of Judges, Deborah ( he, דְּבוֹרָה, ''Dəḇōrā'', "bee") was a prophetess of the God of the Israelites, the fourth Judge of pre-monarchic Israel and the only female judge mentioned in the Bible. Many scholars ...
, an Old Testament prophet; and
Mary Magdalene Mary Magdalene (sometimes called Mary of Magdala, or simply the Magdalene or the Madeleine) was a woman who, according to the four canonical gospels, traveled with Jesus as one of his followers and was a witness to crucifixion of Jesus, his cru ...
, a follower of
Jesus Jesus, likely from he, יֵשׁוּעַ, translit=Yēšūaʿ, label=Hebrew/Aramaic ( AD 30 or 33), also referred to as Jesus Christ or Jesus of Nazareth (among other names and titles), was a first-century Jewish preacher and religious ...
. 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
Muhammad Muhammad ( ar, مُحَمَّد;  570 – 8 June 632 Common Era, CE) was an Arab religious, social, and political leader and the founder of Islam. According to Muhammad in Islam, Islamic doctrine, he was a prophet Divine inspiration, di ...
's daughter
Fatima Fāṭima bint Muḥammad ( ar, فَاطِمَة ٱبْنَت مُحَمَّد}, 605/15–632 CE), commonly known as Fāṭima al-Zahrāʾ (), was the daughter of the Islamic prophet Muhammad and his wife Khadija. Fatima's husband was Ali, th ...
. The hand is made up of the stars α Cas, β Cas, γ Cas, δ Cas, ε Cas, and η Cas. The arm is made up of the stars α Per, γ Per, δ Per, ε Per, η Per, and ν Per. 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. Other cultures see a hand or moose antlers in the pattern. These include the
Sámi The Sámi ( ; also spelled Sami or Saami) are a Finno-Ugric-speaking people inhabiting the region of Sápmi (formerly known as Lapland), which today encompasses large northern parts of Norway, Sweden, Finland, and of the Murmansk Oblast, Ru ...
, for whom the W of Cassiopeia forms an elk antler. The Chukchi of
Siberia Siberia ( ; rus, Сибирь, r=Sibir', p=sʲɪˈbʲirʲ, a=Ru-Сибирь.ogg) is an extensive geographical region, constituting all of North Asia, from the Ural Mountains in the west to the Pacific Ocean in the east. It has been a part of ...
similarly saw the five main stars as five reindeer stags. The people of the
Marshall Islands The Marshall Islands ( mh, Ṃajeḷ), officially the Republic of the Marshall Islands ( mh, Aolepān Aorōkin Ṃajeḷ),'' () is an independent island country and microstate near the Equator in the Pacific Ocean, slightly west of the Internati ...
saw Cassiopeia as part of a great porpoise constellation. The main stars of Cassiopeia make its tail, Andromeda and
Triangulum Triangulum is a small constellation in the northern sky. Its name is Latin for "triangle", derived from its three brightest stars, which form a long and narrow triangle. Known to the ancient Babylonians and Greeks, Triangulum was one of the 48 ...
form its body, and
Aries Aries may refer to: *Aries (astrology), an astrological sign *Aries (constellation), a constellation of stars in the zodiac Arts, entertainment and media * ''Aries'' (album), by Luis Miguel, 1993 * ''Aries'' (EP), by Alice Chater, 2020 * "Aries" ...
makes its head. In
Hawaii Hawaii ( ; haw, Hawaii or ) is a state in the Western United States, located in the Pacific Ocean about from the U.S. mainland. It is the only U.S. state outside North America, the only state that is an archipelago, and the only stat ...
, 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 Pukapuka, formerly Danger Island, is a coral atoll in the northern group of the Cook Islands in the Pacific Ocean. It is one of most remote islands of the Cook Islands, situated about northwest of Rarotonga. On this small island, an ancient ...
saw the figure of Cassiopeia as a distinct constellation called ''Na Taki-tolu-a-Mataliki''.


Characteristics

Covering 598.4 square degrees and hence 1.451% of the sky, Cassiopeia ranks 25th of the 88 constellations in area. 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
International Astronomical Union The International Astronomical Union (IAU; french: link=yes, Union astronomique internationale, UAI) is a nongovernmental organisation with the objective of advancing astronomy in all aspects, including promoting astronomical research, outreac ...
in 1922, is "Cas". The official constellation boundaries, as set by Belgian astronomer
Eugène Delporte Eugene is a common male given name that comes from the Greek εὐγενής (''eugenēs''), "noble", literally "well-born", from εὖ (''eu''), "well" and γένος (''genos''), "race, stock, kin".equatorial coordinate system The equatorial coordinate system is a celestial coordinate system widely used to specify the positions of celestial objects. It may be implemented in spherical or rectangular coordinates, both defined by an origin at the centre of Earth, a fund ...
, the
right ascension Right ascension (abbreviated RA; symbol ) is the angular distance of a particular point measured eastward along the celestial equator from the Sun at the March equinox to the (hour circle of the) point in question above the earth. When paired w ...
coordinates of these borders lie between and , while the
declination In astronomy, declination (abbreviated dec; symbol ''δ'') is one of the two angles that locate a point on the celestial sphere in the equatorial coordinate system, the other being hour angle. Declination's angle is measured north or south of the ...
coordinates are between 77.69° and 46.68°. Its position in the Northern Celestial Hemisphere means that the whole constellation is visible to observers north of 12°S. 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.


Features


Stars

The German cartographer Johann Bayer used the Greek letters
Alpha Alpha (uppercase , lowercase ; grc, ἄλφα, ''álpha'', or ell, άλφα, álfa) is the first letter of the Greek alphabet. In the system of Greek numerals, it has a value of one. Alpha is derived from the Phoenician letter aleph , whic ...
through
Omega Omega (; capital: Ω, lowercase: ω; Ancient Greek ὦ, later ὦ μέγα, Modern Greek ωμέγα) is the twenty-fourth and final letter in the Greek alphabet. In the Greek numeric system/isopsephy (gematria), it has a value of 800. The wo ...
, and then A and B, to label the most prominent 26 stars in the constellation.
Upsilon Upsilon (, ; uppercase Υ, lowercase υ; el, ''ýpsilon'' ) or ypsilon is the 20th letter of the Greek alphabet. In the system of Greek numerals, grc, Υʹ, label=none has a value of 400. It is derived from the Phoenician waw . Etym ...
was later found to be two stars and labelled Upsilon1 and Upsilon2 by
John Flamsteed John Flamsteed (19 August 1646 – 31 December 1719) was an English astronomer and the first Astronomer Royal. His main achievements were the preparation of a 3,000-star catalogue, ''Catalogus Britannicus'', and a star atlas called '' Atlas C ...
. B Cassiopeiae was in fact the supernova known as
Tycho's Supernova SN 1572 ('' Tycho's Supernova'', ''Tycho's Nova''), or B Cassiopeiae (B Cas), was a supernova of Type Ia in the constellation Cassiopeia, one of eight supernovae visible to the naked eye in historical records. It appeared in early November 1572 ...
. Within the constellation's borders, there are 157 stars brighter than or equal to
apparent magnitude Apparent magnitude () is a measure of the brightness of a star or other astronomical object observed from Earth. An object's apparent magnitude depends on its intrinsic luminosity, its distance from Earth, and any extinction of the object's li ...
 6.5.


'W' asterism

The five brightest stars of Cassiopeia – Alpha, Beta, Gamma, Delta, and Epsilon Cassiopeiae – form the characteristic W-shaped asterism. All five are prominent naked eye stars, three are noticeably
variable Variable may refer to: * Variable (computer science), a symbolic name associated with a value and whose associated value may be changed * Variable (mathematics), a symbol that represents a quantity in a mathematical expression, as used in many ...
, and a fourth is a suspected low amplitude variable. The asterism is oriented as a W when below 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 The zenith (, ) is an imaginary point directly "above" a particular location, on the celestial sphere. "Above" means in the vertical direction (plumb line) opposite to the gravity direction at that location (nadir). The zenith is the "highest" ...
) and the W appears inverted. Alpha Cassiopeiae, traditionally called Schedar (from the Arabic ''Al Sadr'', "the breast"), is a four-star system. The primary dominates, an orange-hued
giant In folklore, giants (from Ancient Greek: '' gigas'', cognate giga-) are beings of human-like appearance, but are at times prodigious in size and strength or bear an otherwise notable appearance. The word ''giant'' is first attested in 1297 fr ...
of magnitude 2.2, 228 ± 2 light-years from Earth. With a
luminosity Luminosity is an absolute measure of radiated electromagnetic power (light), the radiant power emitted by a light-emitting object over time. In astronomy, luminosity is the total amount of electromagnetic energy emitted per unit of time by a st ...
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
B-type main-sequence star A B-type main-sequence star (B V) is a main-sequence (hydrogen-burning) star of spectral type B and luminosity class V. These stars have from 2 to 16 times the mass of the Sun and surface temperatures between 10,000 and 30,000 K. B-type star ...
. Magnitude 8.9 yellow dwarf companion (B) is widely separated; companions (C and D) are closer and magnitudes 13 and 14 respectively. Beta Cassiopeiae, or Caph (meaning "hand"), is a white-hued star of magnitude 2.3, 54.7 ± 0.3 light-years from Earth. 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
critical speed In solid mechanics, in the field of rotordynamics, the critical speed is the theoretical angular velocity that excites the natural frequency of a rotating object, such as a shaft, propeller, leadscrew, or gear. As the speed of rotation approache ...
, Caph completes a full rotation every 1.12 days. This is giving the star an oblate spheroid shape with an equatorial bulge that is 24% larger than the polar radius. It is a
Delta Scuti variable A Delta Scuti variable (sometimes termed dwarf cepheid when the V-band amplitude is larger than 0.3 mag.) is a subclass of young pulsating star. These variables as well as classical cepheids are important standard candles and have been used to es ...
with a small amplitude and period of 2.5 hours.
Gamma Cassiopeiae Gamma Cassiopeiae, Latinized from γ Cassiopeiae, is a bright star at the center of the distinctive "W" asterism in the northern circumpolar constellation of Cassiopeia. Although it is a fairly bright star with an apparent visual mag ...
is the prototype 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. It is 550 ± 10 light-years from Earth. Delta Cassiopeiae, also known as Ruchbah or Rukbat, meaning "knee," is a possible Algol-type
eclipsing binary A binary star is a system of two stars that are gravitationally bound to and in orbit around each other. Binary stars in the night sky that are seen as a single object to the naked eye are often resolved using a telescope as separate stars, in w ...
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., but this has never been confirmed. It is 99.4 ± 0.4 light-years from Earth.
Epsilon Cassiopeiae Epsilon Cassiopeiae or ε Cassiopeiae, officially named Segin (), is a single star in the northern constellation of Cassiopeia. With an apparent visual magnitude of 3.4, this is one of the brightest stars in the constellation. The dis ...
has an apparent magnitude of 3.3. Located 410 ± 20 light-years from Earth, 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
Be star Be stars are a heterogeneous set of stars with B spectral types and emission lines. A narrower definition, sometimes referred to as ''classical Be stars'', is a non-supergiant B star whose spectrum has, or had at some time, one or more Balmer e ...
s—rapidly spinning stars that throw off a ring or shell of matter.


Fainter stars

The next seven brightest stars in Cassiopeia are also all confirmed or suspected variable stars, including 50 Cassiopeiae which was not given a Greek letter by Bayer and is a suspected variable with a very small amplitude. Zeta Cassiopeiae (Fulu) is a suspected
slowly pulsating B-type star A slowly pulsating B-type star (SPB), formerly known as a 53 Persei variable, is a type of pulsating variable star. They may also be termed a long-period pulsating B star (LPB). As the name implies, they are main-sequence stars of spectral type B2 ...
.
Eta Cassiopeiae Eta Cassiopeiae (η Cassiopeiae, abbreviated Eta Cas, η Cas) is a binary star system in the northern constellation of Cassiopeia. Its binary nature was first discovered by William Herschel in August 1779. Based upon parallax meas ...
(Achird) is a spectroscopic binary star with a period of 480 years, and a suspected
RS Canum Venaticorum variable An RS Canum Venaticorum variable is a type of variable star. The variable type consists of close binary stars having active chromospheres which can cause large stellar spots. These spots are believed to cause variations in their observed luminosi ...
. 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. Kappa Cassiopeiae is a
blue supergiant A blue supergiant (BSG) is a hot, luminous star, often referred to as an OB supergiant. They have luminosity class I and spectral class B9 or earlier. Blue supergiants are found towards the top left of the Hertzsprung–Russell diagram, above ...
of spectral type BC0.7Ia that is some 302,000 times as luminous as the Sun and has 33 times its diameter. It is a
runaway star In astronomy, stellar kinematics is the Observational astronomy, observational study or measurement of the kinematics or motions of stars through space. Stellar kinematics encompasses the measurement of stellar Velocity, velocities in the Milky W ...
, moving at around 2.5 million mph relative to its neighbors (1,100 kilometers per second). Its magnetic field and wind of particles creates a visible
bow shock In astrophysics, a bow shock occurs when the magnetosphere of an astrophysical object interacts with the nearby flowing ambient plasma such as the solar wind. For Earth and other magnetized planets, it is the boundary at which the speed of th ...
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. Theta Cassiopeiae, named Marfak, is a suspected variable star whose brightness changes by less than a tenth of a magnitude. Iota Cassiopeiae is a
triple star A star system or stellar system is a small number of stars that orbit each other, bound by gravitational attraction. A large group of stars bound by gravitation is generally called a '' star cluster'' or '' galaxy'', although, broadly speak ...
142 light-years from Earth. The primary is a white-hued star of magnitude 4.5 and an α2 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. Omicron Cassiopeiae is a triple star and the primary is another γ Cassiopeiae variable. 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. 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.
Rho Cassiopeiae Rho Cassiopeiae (; ρ Cas, ρ Cassiopeiae) is a yellow hypergiant star in the constellation Cassiopeia. It is about from Earth, yet can still be seen by the naked eye as it is over 300,000 times brighter than the Sun. On average it has a ...
is a semi-regular pulsating variable
yellow hypergiant A yellow hypergiant (YHG) is a massive star with an extended atmosphere, a spectral class from A to K, and, starting with an initial mass of about 20–60 solar masses, has lost as much as half that mass. They are amongst the most visually lumino ...
, among the most luminous stars in the galaxy at approximately . 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
V509 Cassiopeiae V509 Cassiopeiae (V509 Cas or HR 8752) is one of two yellow hypergiant stars found in the constellation Cassiopeia, which also contains Rho Cassiopeiae. HR 8752 is around 15,700 light-years from Earth. It has an apparent magnitude that ...
, 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, as well as
6 Cassiopeiae 6 Cassiopeiae (6 Cas) is a white hypergiant in the constellation Cassiopeia, and a small-amplitude variable star. System 6 Cassiopeiae A is a white A2.5 type hypergiant. It is about 25 times as massive as the Sun and 200,000 times a ...
which is a hotter white
hypergiant A hypergiant (luminosity class 0 or Ia+) is a very rare type of star that has an extremely high luminosity, mass, size and mass loss because of its extreme stellar winds. The term ''hypergiant'' is defined as luminosity class 0 (zero) in the MK ...
. It also hosts the red supergiant
PZ Cassiopeiae PZ Cassiopeiae is a red supergiant star located in the constellation of Cassiopeia (constellation), Cassiopeia, and a semi-regular variable star. Characteristics PZ Cassiopeiae is a luminous red supergiant star, one of the List of larg ...
, which is one of the largest known stars with an estimate of and is also a semiregular variable. Between 240,000 and 270,000 times as luminous as the Sun, it is around 9,160 light-years distant from Earth. AO Cassiopeiae is a
binary system A binary system is a system of two astronomical bodies which are close enough that their gravitational attraction causes them to orbit each other around a barycenter ''(also see animated examples)''. More restrictive definitions require that th ...
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
Sun The Sun is the star at the center of the Solar System. It is a nearly perfect ball of hot plasma, heated to incandescence by nuclear fusion reactions in its core. The Sun radiates this energy mainly as light, ultraviolet, and infrared radi ...
. The two massive stars are so close to each other they distort each other into egg-shapes. Tycho Brahe's supernova was visible within Cassiopeia, and the star
Tycho G Tycho G has been proposed as the surviving binary companion star of the SN 1572 supernova event. The star is located about light-years away in the constellation Cassiopeia. It is a subgiant, similar to the Sun in temperature, but mor ...
is suspected of being the donor of the material that triggered that explosion.


Deep-sky objects

A rich section of the
Milky Way The Milky Way is the galaxy that includes our Solar System, with the name describing the galaxy's appearance from Earth: a hazy band of light seen in the night sky formed from stars that cannot be individually distinguished by the naked eye ...
runs through Cassiopeia, stretching from
Perseus In Greek mythology, Perseus (Help:IPA/English, /ˈpɜːrsiəs, -sjuːs/; Greek language, Greek: Περσεύς, Romanization of Greek, translit. Perseús) is the legendary founder of Mycenae and of the Perseid dynasty. He was, alongside Cadmus ...
towards Cygnus, and it contains a number of
open cluster An open cluster is a type of star cluster made of up to a few thousand stars that were formed from the same giant molecular cloud and have roughly the same age. More than 1,100 open clusters have been discovered within the Milky Way galaxy, and ...
s, young luminous galactic disc stars, and
nebula A nebula ('cloud' or 'fog' in Latin; pl. nebulae, nebulæ or nebulas) is a distinct luminescent part of interstellar medium, which can consist of ionized, neutral or molecular hydrogen and also cosmic dust. Nebulae are often star-forming regio ...
e. The
Heart Nebula The Heart Nebula (also known as the Running dog nebula, IC 1805, Sharpless 2-190) is an emission nebula, 7500 light years away from Earth and located in the Perseus Arm of the Galaxy in the constellation Cassiopeia. It was discovered by William ...
and the Soul Nebula are two neighboring
emission nebula An emission nebula is a nebula formed of ionized gases that emit light of various wavelengths. The most common source of ionization is high-energy ultraviolet photons emitted from a nearby hot star. Among the several different types of emissio ...
e about 7,500 light-years away. Two
Messier objects The Messier objects are a set of 110 astronomical objects catalogued by the French astronomer Charles Messier in his ''Catalogue des Nébuleuses et des Amas d'Étoiles'' (''Catalogue of Nebulae and Star Clusters''). Because Messier was only in ...
, M52 (NGC 7654) and 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. 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. Its most prominent member is actually a closer, superimposed double star; it consists of a 7th-magnitude primary and 10th-magnitude secondary. The other prominent open clusters in Cassiopeia are
NGC 457 NGC 457 (also designated Caldwell 13, and known as the Dragonfly Cluster, E.T. Cluster, Owl Cluster, Kachina Doll Cluster or Phi Cassiopeiae Cluster) is an open star cluster in the constellation Cassiopeia. Discovery It was discovered by Wil ...
and
NGC 663 NGC 663 (also known as Caldwell 10) is a young open cluster in the constellation of Cassiopeia. It has an estimated 400 stars and spans about a quarter of a degree across the sky. It can reportedly be detected with the unaided eye, although a tel ...
, both of which have about 80 stars. NGC 457 is looser, and its brightest member is 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. 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. There are two
supernova remnant A supernova remnant (SNR) is the structure resulting from the explosion of a star in a supernova. The supernova remnant is bounded by an expanding shock wave, and consists of ejected material expanding from the explosion, and the interstellar mat ...
s in Cassiopeia. The first, designated 3C 10 or just ''Tycho's Supernova Remnant'', is the aftermath of the supernova called
Tycho's Star SN 1572 ('' Tycho's Supernova'', ''Tycho's Nova''), or B Cassiopeiae (B Cas), was a supernova of Type Ia in the constellation Cassiopeia, one of eight supernovae visible to the naked eye in historical records. It appeared in early November 1572 ...
. It was observed in 1572 by
Tycho Brahe Tycho Brahe ( ; born Tyge Ottesen Brahe; generally called Tycho (14 December 154624 October 1601) was a Danish astronomer, known for his comprehensive astronomical observations, generally considered to be the most accurate of his time. He was k ...
and now exists as a bright object in the
radio spectrum The radio spectrum is the part of the electromagnetic spectrum with frequencies from 0  Hz to 3,000 GHz (3  THz). Electromagnetic waves in this frequency range, called radio waves, are widely used in modern technology, particula ...
. Within the 'W' asterism formed by Cassiopeia's five major stars lies
Cassiopeia A Cassiopeia A (Cas A) () is a supernova remnant (SNR) in the constellation Cassiopeia and the brightest extrasolar radio source in the sky at frequencies above 1 GHz. The supernova occurred approximately away within the Milky Way ...
(Cas A). It is the remnant of a
supernova A supernova is a powerful and luminous explosion of a star. It has the plural form supernovae or supernovas, and is abbreviated SN or SNe. This transient astronomical event occurs during the last evolutionary stages of a massive star or when ...
that took place approximately 300 years ago (as observed now from Earth; it is 10,000 light-years away), and has the distinction of being the strongest radio source observable outside the
Solar System The Solar SystemCapitalization of the name varies. The International Astronomical Union, the authoritative body regarding astronomical nomenclature, specifies capitalizing the names of all individual astronomical objects but uses mixed "Solar S ...
. It was perhaps observed as a faint star in 1680 by
John Flamsteed John Flamsteed (19 August 1646 – 31 December 1719) was an English astronomer and the first Astronomer Royal. His main achievements were the preparation of a 3,000-star catalogue, ''Catalogus Britannicus'', and a star atlas called '' Atlas C ...
. It was also the subject of the first image returned by the
Chandra X-Ray Observatory The Chandra X-ray Observatory (CXO), previously known as the Advanced X-ray Astrophysics Facility (AXAF), is a Flagship-class space telescope launched aboard the during STS-93 by NASA on July 23, 1999. Chandra is sensitive to X-ray sources 1 ...
in the late 1990s. The shell of matter expelled from the star is moving at per second; it has a temperature of 30,000
kelvin The kelvin, symbol K, is the primary unit of temperature in the International System of Units (SI), used alongside its prefixed forms and the degree Celsius. It is named after the Belfast-born and University of Glasgow-based engineer and phys ...
s on average.
NGC 457 NGC 457 (also designated Caldwell 13, and known as the Dragonfly Cluster, E.T. Cluster, Owl Cluster, Kachina Doll Cluster or Phi Cassiopeiae Cluster) is an open star cluster in the constellation Cassiopeia. Discovery It was discovered by Wil ...
is another open cluster in Cassiopeia, also called the
E.T. ''E.T. the Extra-Terrestrial'' (or simply ''E.T.'') is a 1982 American science fiction film produced and directed by Steven Spielberg and written by Melissa Mathison. It tells the story of Elliott, a boy who befriends an extraterrestrial, dub ...
Cluster, the Owl Cluster, and Caldwell 13. The cluster was discovered in 1787 by
William Herschel Frederick William Herschel (; german: Friedrich Wilhelm Herschel; 15 November 1738 – 25 August 1822) was a German-born British astronomer and composer. He frequently collaborated with his younger sister and fellow astronomer Caroline H ...
. It has an overall magnitude of 6.4 and is approximately 10,000 light-years from Earth, lying in the
Perseus arm The Perseus Arm is one of two major spiral arms of the Milky Way galaxy. The second major arm is called the Scutum–Centaurus Arm. The Perseus Arm begins from the distal end of the long Milky Way central bar. Previously thought to be 13,000 lig ...
of the
Milky Way The Milky Way is the galaxy that includes our Solar System, with the name describing the galaxy's appearance from Earth: a hazy band of light seen in the night sky formed from stars that cannot be individually distinguished by the naked eye ...
. However, its most prominent member, the
double star In observational astronomy, a double star or visual double is a pair of stars that appear close to each other as viewed from Earth, especially with the aid of optical telescopes. This occurs because the pair either forms a binary star (i.e. a bi ...
Phi Cassiopeiae, is far closer – between 1000 and 4000 light-years away. NGC 457 is fairly rich; it is a
Shapley class Shapley is a surname that might refer to one of the following: * Lieutenant General Alan Shapley (1903–1973), of the U.S. Marine Corps, was a survivor the sinking of the USS Arizona in the attack on Pearl Harbor * Harlow Shapley (1885–1972), Am ...
e and
Trumpler class An open cluster is a type of star cluster made of up to a few thousand stars that were formed from the same giant molecular cloud and have roughly the same age. More than 1,100 open clusters have been discovered within the Milky Way galaxy, a ...
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. Two members of the
Local Group The Local Group is the galaxy group that includes the Milky Way. It has a total diameter of roughly , and a total mass of the order of . It consists of two collections of galaxies in a "dumbbell" shape: the Milky Way and its satellites form ...
of galaxies are in Cassiopeia.
NGC 185 NGC 185 (also known as Caldwell 18) is a dwarf spheroidal galaxy located 2.08 million light-years from Earth, appearing in the constellation Cassiopeia. It is a member of the Local Group, and is a satellite of the Andromeda Galaxy (M31). NGC ...
is a magnitude 9.2
elliptical galaxy An elliptical galaxy is a type of galaxy with an approximately ellipsoidal shape and a smooth, nearly featureless image. They are one of the four main classes of galaxy described by Edwin Hubble in his Hubble sequence and 1936 work ''The R ...
of type E0, 2 million light-years away. Slightly dimmer and more distant
NGC 147 NGC 147 (also known as DDO3 or Caldwell 17) is a dwarf spheroidal galaxy about 2.58 Mly away in the constellation Cassiopeia. NGC 147 is a member of the Local group of galaxies and a satellite galaxy of the Andromeda Galaxy (M31). It forms a ...
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 Andromeda, both
dwarf galaxies A dwarf galaxy is a small galaxy composed of about 1000 up to several billion stars, as compared to the Milky Way's 200–400 billion stars. The Large Magellanic Cloud, which closely orbits the Milky Way and contains over 30 billion stars, is s ...
are gravitationally bound to the far larger
Andromeda Galaxy The Andromeda Galaxy (IPA: ), also known as Messier 31, M31, or NGC 224 and originally the Andromeda Nebula, is a barred spiral galaxy with the diameter of about approximately from Earth and the nearest large galaxy to the Milky Way. The gala ...
.
IC 10 IC 10 is an irregular galaxy in the constellation Cassiopeia. It was discovered by Lewis Swift in 1887 and in 1935 Nicholas Mayall became the first to suggest that the object is extragalactic. Edwin Hubble suspected it might belong to the Loc ...
is an irregular galaxy that is the closest known
starburst galaxy A starburst galaxy is one undergoing an exceptionally high rate of star formation, as compared to the long-term average rate of star formation in the galaxy or the star formation rate observed in most other galaxies. For example, the star formatio ...
and the only one in the Local Group of galaxies. Cassiopeia also contains part of the closest galaxy group to our Local Group, the
IC 342/Maffei Group The IC 342/Maffei Group (also known as the IC 342 Group or the Maffei 1 Group) corresponds to one or two galaxy groups close to the Local Group. The member galaxies are mostly concentrated around either IC 342 or Maffei 1, which would be the brig ...
. The galaxies
Maffei 1 Maffei 1 is a massive elliptical galaxy in the constellation Cassiopeia. Once believed to be a member of the Local Group of galaxies, it is now known to belong to a separate group, the IC 342/Maffei Group. It was named after Paolo Maffei, who ...
and
Maffei 2 Maffei 2 is an intermediate spiral galaxy about 10 million light-years away in the constellation Cassiopeia. Maffei 2 and Maffei 1 were both discovered by Paolo Maffei in 1968 from their infrared emission. Maffei 2 lies in the Zone of Avoidan ...
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). Kassiopeia.labelled.P1023186.png, Cassiopeia with indication of χ Persei (NGC 884) and h Persei (NGC 869) as well as the star clusters
NGC 654 NGC 654 is an open cluster in the constellation Cassiopeia. It was discovered by William Herschel in 1787. With apparent magnitude 6.5, it can be observed by binoculars. It is located 2,5° northeast of the star Delta Cassiopeiae. In the same low ...
,
NGC 663 NGC 663 (also known as Caldwell 10) is a young open cluster in the constellation of Cassiopeia. It has an estimated 400 stars and spans about a quarter of a degree across the sky. It can reportedly be detected with the unaided eye, although a tel ...
, NGC 581 (Messier 103),
NGC 457 NGC 457 (also designated Caldwell 13, and known as the Dragonfly Cluster, E.T. Cluster, Owl Cluster, Kachina Doll Cluster or Phi Cassiopeiae Cluster) is an open star cluster in the constellation Cassiopeia. Discovery It was discovered by Wil ...
, NGC 225, NGC 7788, NGC 7790, NGC 7789 and NGC 7654 (Messier 52).


Meteor shower

The December Phi Cassiopeiids are a recently discovered early December
meteor shower A meteor shower is a celestial event in which a number of meteors are observed to radiate, or originate, from one point in the night sky. These meteors are caused by streams of cosmic debris called meteoroids entering Earth's atmosphere at extre ...
that 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.


Namesakes

USS ''Cassiopeia'' (AK-75) was a
United States Navy The United States Navy (USN) is the maritime service branch of the United States Armed Forces and one of the eight uniformed services of the United States. It is the largest and most powerful navy in the world, with the estimated tonnage ...
''Crater''-class cargo ship named after the constellation.


See also

* Cassiopeia (Chinese astronomy)


References


Explanatory notes


Citations


General and cited sources

* * * * *


External links


The Deep Photographic Guide to the Constellations: Cassiopeia





Warburg Institute Iconographic Database (medieval and early modern images of Cassiopeia)
{{DEFAULTSORT:Cassiopeia (Constellation) Constellations Northern constellations Constellations listed by Ptolemy