Cassiopeia (constellation)

Cassiopeia is one of the constellations compiled in Ptolemy's star catalogue, the Almagest, from the 2nd century. Easily recognizable by its five bright stars that form a well-known asterism in the northern circumpolar sky. Cassiopeia points to north (and to the pole star) by pointing from its "M" or "W" ends. On the other side is the Big Dipper Chariot. Being so easy to recognize, it is widely used to find the north when it is not possible to use the Big Dipper for this purpose, when it is not visible in skies of temperate latitudes (less than 35°N - Canary Islands).

Due to its proximity to the North Pole, this constellation is circumpolar boreal, that is, it is always visible above the northern horizon from 45-50° north latitude, the latitude of cities like Berlin or London. For observers from the southern hemisphere, this constellation will always remain invisible if the latitude of the location is less than its minimum declination, that is, 43°S.

The best month to see Cassiopeia is October, its most characteristic asterism being the one formed by its five brightest stars (from west to east): Caph, Schedar, Cih, Ruchbah and Segin. These stars take the characteristic shape of an "M". It is in this month when it has the best visibility for southern observers, who will see it forming an "M" very low on the northern horizon.

On the other hand, the Sun, observed from nearby Alpha Centauri, would appear in the constellation Cassiopeia as a 0.5 magnitude star. The well-known "W" of Cassiopeia would appear in a zigzag shape, with the Sun located to the extreme left close to ε Cassiopeiae.

Notable features

The following table lists the most significant and brightest stars in Cassiopeia:

γ Cassiopeiae, known as Tsih or Cih, is located in the center of the “W” or “M”. It is a blue subgiant of spectral type B0.5IVe with a temperature of more than 28,000 K. Its high rotation speed, greater than 432 km/s, makes it very flattened towards the equator, which causes loss of mass. stellar that forms a "decretion" disk around the star. Such mass loss causes brightness variations, with γ Cassiopeiae being the archetype of a class of eruptive variables to which it gives its name, Gamma Cassiopeiae variables. Among X-ray emitting OB stars, the peculiar characteristics of their emission are unique for such a star.

The constellation of Casiopea

α Cassiopeiae, officially called Schedar, is an orange giant of spectral type K0IIIa whose radius—calculated from the measurement of its angular diameter—is 42 times greater than the solar radius.Caph (β Cassiopeiae) It is a yellow-white subgiant 54.5 light years from Earth. 28 times more luminous than the Sun, it is a Delta Scuti variable, the brightest of this type of variable, with a brightness fluctuation of 0.06 magnitudes.

Ruchbah (δ Cassiopeiae) is an eclipsing binary whose two components orbit each other over a period of 759 days. The main star is a white subgiant of spectral type A5IV. Another star with its own name is Fulu —official name of ζ Cassiopeiae—, a B2IV-type blue subgiant classified as a slow pulsating variable (SPB), a cold and dim version of the Beta Cephei variables. On the other hand, κ Cassiopeiae is a distant supergiant about 3,000 light-years; it is an Alpha Cygni variable and a runaway star that is in an arc collision with its surrounding medium.

Cassiopeia contains two stars that are among the most luminous in the galaxy and can be seen with the naked eye: ρ Cassiopeiae and V509 Cassiopeiae. Both are yellow hypergiants, a particularly rare class of objects of which there are only seven known in the Milky Way. The parameters of these stars are outsized: the luminosity of ρ Cassiopeiae, the largest part in the visible spectrum, equals 550,000 Suns, while the diameter of V509 Cassiopeiae is 400 times larger than the solar diameter.

Several Mira variables can be observed in Cassiopeia, such as R Cassiopeiae, S Cassiopeiae and WY Cassiopeiae. These last two are S-type stars —characterized by showing very intense zirconium monoxide bands— of spectral type S3.4e-S5.8e and S6.5pe respectively.

There are several stars in the constellation with planets. HD 7924 is a K0V-type orange dwarf with three planets, one of them of the "super-Earth" type but in a very close orbit to its star, equivalent to 5.7% of the distance between the Earth and the Sun. Likewise, Gliese 22 is a multiple system composed of three red dwarfs, two of them separated by about 1.25 au, and a third one more external —at 41 au— that takes 320 years to complete an orbit around the inner pair. Around this solitary component of the system, the presence of an object has been detected —still pending confirmation— that could be a giant planet or a brown dwarf, since a mass 13 times greater than that of Jupiter is the commonly accepted limit. that separates both types of objects. Especially interesting is Gliese 892 (HD 219134), an orange dwarf with at least five planets; the innermost, HD 219134 b, is a rocky "super-Earth" according to its size (1.6 times the size of Earth) and density (6.4 g/cm³).

In this constellation is located 3C 58, a name given to a pulsar and the surrounding synchrotron nebula. The central pulsar (PSR J0205+6449) is a rapidly rotating neutron star, surrounded by a bright X-ray emitting torus. Although it was initially thought that 3C 58 might not be a neutron star, but a star of quarks —exotic star in which, due to its high density, matter exists in the form of unconfined quarks—, later studies rule out this hypothesis.

Image of the remnant of SN 1572 in X-ray light obtained from the Chandra observatory.

Cassiopeia contains the cluster M103, one of the most distant open clusters, lying at a distance of 8,000 - 9,500 light-years. Another cluster in the Messier catalogue, M52, is also in this constellation. There is no consensus regarding its position with respect to Earth: various studies place M52 at an uncertain distance between 3,000 and 7,000 light years.

Another object of interest is Cassiopeia A (Cas A), a supernova remnant and the brightest astronomical radio source outside the solar system at frequencies above 1 GHz. The supernova that caused this remnant was located within the Milky Way at a distance of approximately 11,000 light-years. The expanding cloud of supernova remnant material is now approximately 10 light-years across.

SN 1572, one of the most important events in the history of astronomy, was a supernova that appeared in this constellation and was observed, among others, by Tycho Brahe and Jerónimo Muñoz in 1572. This supernova was classified as type I based on their historical light curve shortly after type I and type II supernovae were first defined.

Main Stars

Image of γ Cassiopeiae and associated nebulae IC63 and IC59.

• α Cassiopeiae (Schedar or Schedir), giant orange star, the brightest constellation with apparent magnitude 2.24.
• β Cassiopeiae (Caph), of magnitude 2,28, is a white-yellow subgigant and a Delta Scuti variable, the most brilliant within this type of variables.
• γ Cassiopeiae (Tsih), located in the center of the W of constellation, is an eruptive variable star, prototype of the Gamma Cassiopeiae variables. In its maximum intensity it exceeds in brightness to Schedar.
• δ Cassiopeiae (Ksora or Ruchbah), white and binary star of magnitude 2,66.
• ε Cassiopeiae (Segin), a blue giant of magnitude 3.38.
• ج Cassiopeiae (Fulu), blue star and slow pulsating variable (SPB) of magnitude 3.67.
• Cristian Cassiopeiae (Achird), double star to 19 light years with a very similar primary to the Sun.
• θ Cassiopeiae, also known as Marfak, a white star at 137 light years.
• . Cassiopeiae, a triple star system when seen with a small telescope.

κ Cassiopeiae and his shock arch. Infrared image of the Spitzer telescope (NASA/JPL-Caltech)

• κ Cassiopeiae, blue supergigante northeast of Caph at about 4100 light years.
• λ Cassiopeiae, binary star where its two components are two very similar white-blue stars.
• μ Cassiopeiae, a sub-enan binary star only 24.6 light years from Earth. Share the name of Marfak with θ Cassiopeiae.
• ? Cassiopeiae, two stars separated 33.6 seconds of arc, one of which is a spectroscopic binary.
• ρ Cassiopeiae and V509 Cassiopeiae, yellow hypergiant stars, of the most luminous in our galaxy.
• σ Cassiopeiae, double system with a separation of 3.1 seconds of arc.
• φ Cassiopeiae, a star that appears next to the NGC 457 cluster, although it is not part of it.
• ω Cassiopeiae, blue star of magnitude 4,97.
• 1 Cassiopeiae, hot and massive star of magnitude 4,84.
• 6 Cassiopeiae, very bright white supergiant star of magnitude 5.43.
• 21 Cassiopeiae (YZ Cassiopeiae), an eclipsing binary whose main component is a star with metal lines; a third-largest star completes the system.
• 43 Cassiopeiae, variable Alpha2 Canum Venaticorum of magnitude 5.56.
• 47 Cassiopeiae, white-yellow star of magnitude 5.28.
• R Cassiopeiae, variable Mira whose brightness varies between magnitude 4.7 and 13.50 in a period of 430 days.
• S Cassiopeiae, like the previous one a variable Mira whose period is 612.43 days.
• RZ Cassiopeiae, eclipsing binary and variable Delta Scuti of magnitude 6.26.
• TZ Cassiopeiae and PZ Cassiopeiae, distant red supergiant; the first is an irregular variable of average magnitude 9.04.
• WY Cassiopeiae and WZ Cassiopeiae respectively an S-type star and a carbon star; the latter has an average magnitude 7.06.
• AO Cassiopeiae, an eclipsing binary of magnitude 6,10, whose components are so close that they exchange matter with each other.

Artistic conception of magnetar 4U 0142+61.

• MZ Cassiopeiae and V809 Cassiopeiae, large red supergiant.
• V466 Cassiopeiae and V778 Cassiopeiae, red supergiants; the first is a member of NGC 457.
• HD 7924, orange dwarf with a "supertierra" planet.
• HD 17156, yellow subgiant star with an extrasolar planet.
• Gliese 22 (V547 Cassiopeiae), a multiple star to 33 light years composed of three red dwarfs, where the existence of a planet has been discovered orbiting around the most remote component of the system.
• Gliese 892 and Gliese 75 (HR 511), respectively 21.3 and 32.5 light years of the solar system, both orange dwarfs.
• Gliese 48 and V596 Cassiopeiae, red dwarfs of magnitude 10 and 12 respectively.
• Gliese 49 and V388 Cassiopeiae, pair of red dwarfs that share their own motion.
• 3C 58, neutron star possibly associated with the supernova SN 1181, candidate for star quarks.
• 4U 0142+61, a magnet star with a circum-stellar disk around it.

Deep Sky Objects

Image of the sky centered in Casiopea taken from an obscure site. In the image there are several objects of deep sky, including the Andromeda Galaxy.

Image of NGC 7635 or Nebulae Bubble.

• M52 (NGC 7654), open cluster that can be observed 5° northwest of Caph (β Cassiopeiae). It has 193 probable members on a 9-minute arc radius. AR: 23h 24m 12.0s Dec: +61°35′00′′ (Epoch 2000).
• M103 (NGC 581), wide open cluster 7 located northeast of Ksora (δ Cas). It consists of about 40 members, having the brightest visual magnitude 10.5 and 10.8. AR: 01h 33m 12.0s Dec: +60°42′00′′ (Epoca 2000).
• NGC 457, cluster open to the southwest of Ksora (δ Cas) M. AR: 01h 19m 06.0s Dec: +58°20′000′′ (Epoch 2000).
• NGC 436, near the previous one, is better to observe it with large telescopes. AR: 01h 15m 36.0s Dec: +58°49′00′′ (Epoch 2000).
• NGC 663, apparent volume 7 at coordinates AR: 01h 46m Dec: +61°14′.
• NGC 7635 or Bubble Nebula, emission nebula illuminated by the blue star SAO 20575 (BD+60 2522). AR: 23h 20m 42.0s Dec: +61°12′00′′ (Epoch 2000).
• NGC 7789, open cluster. AR: 23h 57m 00.0s Dec: +56°44′00′′ (Epoca 2000).
• Nebulae IC 1805 and IC 1848.
• NGC 147 and NGC 185, dwarf elliptical galaxies that form part of the Local Group. Both are satellites from the Andromeda galaxy.
• Dwingeloo 1 and Dwingeloo 2, nearby but discovered galaxies only recently by being visually close to the plane of the Milky Way.
• IC 10 irregular star outbreak galaxy member of the Local Group, with the black hole called IC 10 X-1 (desc. 2007).
• Cassiopeia A, remnant of supernova. It is the most intense radio source in the sky beyond our solar system and was among the first sources found in 1947. Other supernova remains in constellation are CTB 1, CTB 109, HB 3 and SNR G127.1+00.5.

Mythology

The Cassiopaean constellation.

Cassiopeia is the mother of Andromeda and wife of Cepheus, king of Ethiopia. Queen Cassiopeia boasted of her beauty, comparing her to the Nereids, daughters of the sea god Nereus, known as the most beautiful creatures of all. This pride was the cause of her misfortune, drawing the wrath of Poseidon, who sent the sea monster Ceto to devastate the kingdom. Trying to save Ethiopia, Cepheus and Cassiopeia consulted an oracle, which told them that the only way to appease the sea god was to offer his daughter as a sacrifice. Andromeda was stripped of her clothes and chained to a rock at the edge of the sea, waiting to die at the hands of Ceto. However, the hero Perseus, who was returning from killing Medusa, fell in love with the young captive and used her severed head to defeat Ceto by turning him into a coral, thereby saving Andromeda's life and eventually marrying Medusa. she.

Not wanting to leave Cassiopeia unpunished, Poseidon placed her in the heavens tied to a chair in such a position that, when the celestial vault rotates, she remains upside down half the time. The constellation resembles this throne, which originally represented an instrument of torture. Cassiopeia is not always represented tied to the chair as a torment; in some later images she holds a mirror, a symbol of her vanity, while in others she holds a palm leaf, a symbolism that is not clear.

In popular culture

Writer Michael Ende named the turtle character in his work Momo after him.

In the first Super Sentai series Himitsu Sentai Goranger, the main villain Black Cross Fuhrer is weak to Cassiopeia's lightning bolts, the Gorangers upon discovering this, decide to use it to finish him off once and for all.

In the 1978 American series Battlestar Galactica, Cassiopeia was the name of a character who practiced prostitution, played by New York actress Laurette Spang.