from Wikipedia Website

Las Pléyades (que significa "palomas" en griego), también conocidas como Objeto Messier 45, Messier 45, M45, Las Siete Hermanas o Cabrillas, es un objeto visible a simple vista en el cielo nocturno con un prominente lugar en la mitología antigua, situado a un costado de la constelación Tauro.

Las Pléyades son un puñado de estrellas muy jóvenes las cuales se sitúan a una distancia aproximada de 450 años luz de la Tierra y están contenidas en un espacio de treinta años luz.

Se formaron aproximadamente hace apenas unos 100 millones de años, durante la era Mesozoica en la Tierra, a partir del colapso de una nube de gas interestelar.

Las estrellas más grandes y brillantes del cúmulo son de color blanco-azulado y cerca de cinco veces más grandes que el Sol.
 

Pléyades

Distancia

La distancia al cúmulo ha sido estimada por muchos métodos, pues es un paso importante en la calibración de las distancias en el universo. El conocimiento exacto de la distancia de las Pléyades le permite a los astrónomos trazar un diagrama de Hertzsprung-Russell, para estimar la distancia a otros cúmulos desconocidos.

Otros métodos pueden entonces extender la escala de distancia, de cúmulos abiertos a galaxias y posteriormente a cúmulos de galaxias, permitiendo construir una escala cósmica de distancias.

Los resultados anteriores al lanzamiento del satélite Hipparcos encontraron que las Pléyades estaban aproximadamente a unos 135 parsec (440 años luz) de la Tierra. Hipparcos causó consternación entre los astrónomos al encontrar una distancia de solamente 118 parsec (384,7 años luz) midiendo el paralaje de algunas estrellas del cúmulo, una técnica que debe de indicar los resultados más directos y exactos. Trabajos más recientes han encontrado que la distancia calculada por Hipparcos era errónea, si bien se desconoce la causa de este error.

La distancia específica de las Pléyades todavía se desconoce, pero actualmente se piensa que la verdadera distancia es mayor que 135 parsec.

 

Composición

El cúmulo tiene unos 12 años luz de diámetro y contiene un total aproximado de 500 estrellas.

Está dominada por estrellas azules jóvenes, de las cuales 8 pueden ser observadas a simple vista dependiendo de las condiciones atmosféricas (cielos muy limpios y ausencia de Luna): Taygeta, Pleione, Merope, Maia, Electra, Celaeno, Atlas y Alcyone

El orden de sus estrellas más brillantes es parecido al de la Osa Mayor y Osa Menor, con una masa total estimada en unas 800 masas solares.

El cúmulo está compuesto en una buena parte por enanas marrones —objetos con menos del 8% de la masa solar, los cuales son demasiado livianos para ser estrellas. Puede que estos objetos constituyan aproximadamente el 25% de la población total del cúmulo, a pesar de que sólo contribuyan al 2% su masa total. También, presentes en el cúmulo están las enanas blancas, las cuales contradicen la posible edad del cúmulo.

Debido a la corta edad del cúmulo, no se espera que las estrellas normales puedan haber evolucionado para convertirse en enanas blancas. Se cree que en vez de ser estrellas individuales de poca o mediana masa, los progenitores de estas estrellas eran masivas y orbitaban en sistemas binarios. Durante su rápida evolución, la transferencia de masa de la estrella más masiva a su acompañante, pudo haber acelerado su evolución hacia una enana blanca.

Las cámaras CCD sirven de ellas para calibrar estas.

 

Otros

Las Pléyades son una prominente vista invernal del hemisferio norte, y conocidas desde la antigüedad.

Son mencionadas en varias escrituras antiguas entre las que se encuentran

• el Mahabharata (Libro 13: Anusasana Parva: Seccion: LXXXVI) en donde se refieren a ellas como krittikas (sánscrito, que se puede traducir como "cortadores", quienes criaron a Kartikeya)

• la Ilíada y la Odisea de Homero

• son mencionadas tres veces en la Biblia

• también son mencionadas en el Popol Vuh (el libro sagrado de los Mayas) bajo el nombre de MOTZ que significa "monton" y que según lo relata dicho libro se originaron cuando "Zipacna el soberbio" mató a 400 guerreros, cuyas almas fueron tomadas por "Gucumatz el Gran Corazón del Cielo" y puestas como estrellas en el espacio, creando así Las Pleyades

Las Pléyades no existían cuando Venus emergió de la nebulosa protosolar hace 4.500 millones de años.

El 4 de marzo de 1769, Charles Messier las incluyó como el No. 45 en su primera lista de nebulosas y cúmulos de estrella, que fue publicada en 1771.

Se ha calculado que las Pléyades tienen un futuro de solamente otros 250 millones de años (Kenneth Glyn Jones); para ese entonces, habrán sido separadas como estrellas individuales (o múltiples) a lo largo de su trayectoria.

Bajo condiciones ideales de observación, se pueden apreciar algunas huellas de nebulosidad, y esto se demuestra en fotografías de larga exposición. Es una nebulosa de reflexión, causada por polvo que refleja la luz azul de las estrellas calientes y jóvenes.

Se piensa a menudo que este polvo fue lo que sobró de la formación del cúmulo, pero con una edad cerca a los 100 millones de años, la cuál es generalmente la más aceptada para este cúmulo, casi todo el polvo originalmente presente habría sido dispersado por la presión de la radiación. Al parecer, el cúmulo está pasando por una región particularmente polvorienta del medio interestelar.

Los estudios demuestran que el polvo responsable de la nebulosidad no está distribuido uniformemente, pero que se concentra principalmente en dos capas a lo largo de la parte que vemos del cúmulo. Estas capas se pudieron haber formado por la desaceleración debido a la presión de la radiación a medida que el polvo se ha ido moviendo hacia las estrellas.

Las principales estrellas son, ordenadas por magnitud:

Los Mayas

Los Mayas basaron su calendario sagrado Tzolkin, en el ciclo de las Pléyades, y creyeron que eran el lugar de origen de su cultura, eran llamadas Tzab-ek o cola de Serpiente de Cascabel, y también las conocían como Las Siete Hermanas.

Pleiades

from Wikipedia Website

The Pleiades, also known as M45, the Seven Sisters, Seven Stars, SED, Matariki (New Zealand), or Subaru (Japan), is an open cluster in the constellation of Taurus.

It is among the nearest star clusters, and is probably the best known, and is certainly the most obvious to the naked eye. It is sometimes referred to as the Maia Nebula, perhaps erroneously considering that the reflection nebulosity surrounding Maia is intrinsic.

The cluster is dominated by hot blue stars which have formed within the last 100 million years. Dust that forms a faint reflection nebulosity around the brightest stars was thought at first to be left over from the formation of the cluster, but is now known to be an unrelated dust cloud that the stars are currently passing through.

Astronomers estimate that the cluster will survive for about another 250 million years, after which it will have dispersed due to gravitational interactions with its galactic neighborhood.
 

Pleiades

Observational history
 

Comet Machholz passes near the Pleiades in early 2005
 

The Pleiades are a prominent sight in winter in the Northern Hemisphere and in summer in the Southern Hemisphere, and have been known since antiquity to cultures all around the world, including the Māori and Australian Aborigines, the Chinese, the Maya (who called them Tzab-ek), the Aztec and the Sioux of North America.

Some Greek astronomers considered them to be a distinct constellation, and they are mentioned by Hesiod, and in Homer's Iliad and Odyssey.

They are also mentioned three times in the Bible (Job 9:9, 38:31; Amos 5:8).

A shorter exposure shows less nebulosity.

The Pleiades (Krittika) are particularly revered in Hindu mythology as the six mothers of the war god Skanda, who developed six faces, one for each of them. Some scholars of Islam suggested that the Pleiades (At-thuraiya) are the Star in Najm which is mentioned in the Quran.
 

They have long been known to be a physically related group of stars rather than any chance alignment.

The Reverend John Michell calculated in 1767 that the probability of a chance alignment of so many bright stars was only 1 in 500,000, and so correctly surmised that the Pleiades and many other clusters of stars must be physically related. When studies were first made of the stars' proper motions, it was found that they are all moving in the same direction across the sky, at the same rate, further demonstrating that they were related.

Charles Messier measured the position of the cluster and included it as M45 in his catalogue of comet-like objects, published in 1771. Along with the Orion Nebula and the Praesepe cluster, Messier's inclusion of the Pleiades has been noted as curious, as most of Messier's objects were much fainter and more easily confused with comets—something which seems scarcely possible for the Pleiades.

A Spitzer image of the Pleiades in infrared light, showing the associated dust.

Credit: NASA/JPL-Caltech

One possibility is that Messier simply wanted to have a larger catalogue than his scientific rival Lacaille, whose 1755 catalogue contained 42 objects, and so he added some bright, well-known objects to boost his list.^[5]

 

Distance

The distance to the Pleiades is an important first step in the so-called cosmic distance ladder, a sequence of distance scales for the whole universe. The size of this first step calibrates the whole ladder, and the scale of this first step has been estimated by many methods. As the cluster is so close to the Earth, its distance is relatively easy to measure.

Accurate knowledge of the distance allows astronomers to plot a Hertzsprung-Russell diagram for the cluster which, when compared to those plotted for clusters whose distance is not known, allows their distances to be estimated. Other methods can then extend the distance scale from open clusters to galaxies and clusters of galaxies, and a cosmic distance ladder can be constructed. Ultimately astronomers' understanding of the age and future evolution of the universe is influenced by their knowledge of the distance to the Pleiades.

Results prior to the launch of the Hipparcos satellite generally found that the Pleiades were about 135 parsecs away from Earth.

Hipparcos caused consternation among astronomers by finding a distance of only 118 parsecs by measuring the parallax of stars in the cluster—a technique which should yield the most direct and accurate results. Later work has consistently found that the Hipparcos distance measurement for the Pleiades was in error, but it is not yet known why the error occurred.^[6]

The distance to the Pleiades is currently thought to be the higher value of about 135 parsecs (roughly 440 light years).

 

Composition
 

X-ray images of the Pleiades reveal the stars with the hottest atmospheres.

Green squares indicate the seven optically brightest stars.

The cluster core radius is about 8 light-years and tidal radius is about 43 light years. The cluster contains over 1000 statistically confirmed members, although this figure excludes unresolved binary stars.

It is dominated by young, hot blue stars, up to 14 of which can be seen with the naked eye depending on local observing conditions. The arrangement of the brightest stars is somewhat similar to Ursa Major and Ursa Minor. The total mass contained in the cluster is estimated to be about 800 solar masses.

The cluster contains many brown dwarfs, which are objects with less than about 8% of the Sun's mass, not heavy enough for nuclear fusion reactions to start in their cores and become proper stars.

They may constitute up to 25% of the total population of the cluster, although they contribute less than 2% of the total mass. Astronomers have made great efforts to find and analyze brown dwarfs in the Pleiades and other young clusters, because they are still relatively bright and observable, while brown dwarfs in older clusters have faded and are much more difficult to study.

Also present in the cluster are several white dwarfs. Given the young age of the cluster normal stars are not expected to have had time to evolve into white dwarfs, a process which normally takes several billion years. It is believed that, rather than being individual low- to intermediate-mass stars, the progenitors of the white dwarfs must have been high-mass stars in binary systems.

Transfer of mass from the higher-mass star to its companion during its rapid evolution would result in a much quicker route to the formation of a white dwarf, although the details of this supposed transfer from a deeper gravity well to a lesser are unexplained.

 

Age and future evolution

Ages for star clusters can be estimated by comparing the Hertzsprung-Russell diagram for the cluster with theoretical models of stellar evolution, and using this technique, ages for the Pleiades of between 75 and 150 million years have been estimated.

The spread in estimated ages is a result of uncertainties in stellar evolution models. In particular, models including a phenomenon known as convective overshoot, in which a convective zone within a star penetrates an otherwise non-convective zone, result in higher apparent ages.

Another way of estimating the age of the cluster is by looking at the lowest-mass objects. In normal main sequence stars, lithium is rapidly destroyed in nuclear fusion reactions, but brown dwarfs can retain their lithium. Due to lithium's very low ignition temperature of 2.5 million kelvins, the highest-mass brown dwarfs will burn it eventually, and so determining the highest mass of brown dwarfs still containing lithium in the cluster can give an idea of its age.

Applying this technique to the Pleiades gives an age of about 115 million years.

The cluster's relative motion will eventually lead it to be located, as seen from Earth many millennia in the future, passing below the feet of what is currently the constellation of Orion. Also, like most open clusters, the Pleiades will not stay gravitationally bound forever, as some component stars will be ejected after close encounters and others will be stripped by tidal gravitational fields.

Calculations suggest that the cluster will take about 250 million years to disperse, with gravitational interactions with giant molecular clouds and the spiral arms of the galaxy also hastening its demise.

 

Reflection nebulosity
 

Hubble Space Telescope image of reflection nebulosity near Merope

Under ideal observing conditions, some hint of nebulosity may be seen around the cluster, and this shows up in long-exposure photographs. It is a reflection nebula, caused by dust reflecting the blue light of the hot, young stars.

It was formerly thought that the dust was left over from the formation of the cluster, but at the age of about 100 million years generally accepted for the cluster, almost all the dust originally present would have been dispersed by radiation pressure. Instead, it seems that the cluster is simply passing through a particularly dusty region of the interstellar medium.

Studies show that the dust responsible for the nebulosity is not uniformly distributed, but is concentrated mainly in two layers along the line of sight to the cluster.

These layers may have been formed by deceleration due to radiation pressure as the dust has moved towards the stars.


 

Names and technical information
 

A map of the Pleiades

The nine brightest stars of the Pleiades are named for the Seven Sisters of Greek mythology: Sterope, Merope, Electra, Maia, Taygete, Celaeno and Alcyone, along with their parents Atlas and Pleione.

As daughters of Atlas, the Hyades were sisters of the Pleiades. The English name of the cluster itself is of Greek origin, though of uncertain etymology. Suggested derivations include: from πλεîν plein, to sail, making the Pleiades the "sailing ones"; from pleos, full or many; or from peleiades, flock of doves.

The following table gives details of the brightest stars in the cluster:
 

Pleiades Bright Stars

In folklore and literature

“Δέδυκε μεν ἀ σελάννα
καὶ Πληΐαδες, μέσαι δὲ
νύκτες πάρα δ᾽ ἔρχετ᾽ ὤρα,
ἔγω δὲ μόνα κατεύδω.

The Moon is set,
And the Pleiades.
Night's half gone,
Time's passing.
I sleep alone now. ”
— Sappho

“ Which maketh Arcturus, Orion, and Pleiades, and the chambers of the south.”
— Job 9:9

“ Can you bind the beautiful Pleiades? Can you loose the cords of Orion? ”
— Job 38:31

“ Slave of the wheel of labor, what to him Are Plato and the swing of Pleiades? ”
— Edwin Markham, The Man With the Hoe

“ Many a night I saw the Pleiads, rising thro' the mellow shade, Glitter like a swarm of fireflies tangled in a silver braid. ”
— Alfred Tennyson, Locksley Hall

“ Can I get two maybe even three of these, Comin' from a space to teach you of the Pleiades. ”
— Red Hot Chili Peppers, "Can't Stop"

“ Though all I knew of a rote universe were those Pleiades loosed in December, I promised you I'd set them to verse so I'd always remember. ”
— Joanna Newsom, "Emily"

“ Last night I saw the Pleiades again,
Faint as a drift of steam
From some tall chimney-stack; ”
— Arthur Adams, "The Pleiades"

The Pleiades' high visibility in the night sky has guaranteed it a special place in many cultures, both ancient and modern. In Greek mythology, they represented the Seven Sisters, while to the Vikings, they were Freyja's hens, and their name in many old European languages compares them to a hen with chicks.

To the Bronze Age people of Europe, such as the Celts (and probably considerably earlier), the Pleiades were associated with mourning and with funerals, since at that time in history, on the cross-quarter day between the autumn equinox and the winter solstice (see Samhain, also Halloween or All Souls Day), which was a festival devoted to the remembrance of the dead, the cluster rose in the eastern sky as the sun's light faded in the evening.

It was from this acronychal rising that the Pleiades became associated with tears and mourning. As a result of precession over the centuries, the Pleiades no longer marked the festival, but the association has nevertheless persisted, and accounts for the significance of the Pleiades astrologically.

The early Monte Alto Culture and others in Guatemala such as Ujuxte and Takalik Abaj, made its early observatories, using the Pleiades and Eta Draconis as reference, they were called the seven sisters, and thought to be their original land.

A bronze disk, 1600 BC, from Nebra, Germany, is one of the oldest known representations of the cosmos.

The Pleiades are top right.

Heliacal risings very often mark important calendar points for ancient peoples.

The heliacal rising of the Pleiades (around June) also begins the new year for the Māori of New Zealand, who call the Pleiades Matariki. There is an analogous holiday in Hawai'i known as Makali'i.

The ancient Aztecs of Mexico and Central America based their calendar upon the Pleiades. Their calendric year began when priests first remarked the asterism rising heliacally in the east, immediately before the sun's dawn light obliterated the view of the stars.

Aztecs called the Pleiades Tianquiztli (meaning "marketplace").

 

Indigenous Australians and Mainland Asians

Depending on the tribe or clan, there are several stories regarding the origins of the Pleiades. Some Indigenous Australian peoples believed the Pleiades was a woman who had been nearly raped by Kidili, the man in the moon.

Another version, often painted by Gabriella Possum Nungurayyi as this is her dreaming (or creation story), daughter of the late Clifford Possum Tjapaltjarri from the Central desert art movement of Papunya, depicts the story of seven Napaltjarri sisters being chased by a man named Jilbi Tjakamarra. He tried to practice love magic to one of the sisters but the sister did not want to be with him and with her sisters, they ran away from him.

They sat down at Uluru to search for honey ants but when they saw Jilbi, they went to Kurlunyalimpa and with the spirits of Uluru, transformed into stars. Jilbi transforms himself into what is commonly known as the Morning Star in Orion's belt, thus continuing to chase the seven sisters across the sky.

Among the Ban Raji, who live in semi-nomadic settlements scattered throughout western Nepal and northern India, the Pleiades are called the "Seven sisters-in-law and one brother-in-law" (Hatai halyou daa salla). Ban Rajis note that when the Pleiades rises up over the mountain each night, they feel happy to see their ancient kin (Fortier 2008:in press).

On a more practical note, Ban Rajis can tell that evening has arrived, indicating that it is about eight o’clock by local time standards when their star-kin rise above the Nepali mountains bordering the Kali River.

 

Native Americans

The Lakota Tribe of North America had a legend that linked the origin of the Pleiades to Devils Tower. According to the Seris (of northwestern Mexico), these stars are seven women who are giving birth. The constellation is known as Cmaamc, which is apparently an archaic plural of the noun cmaam "woman".

It was common among the indigenous peoples of the Americas to measure keenness of vision by the number of stars the viewer could see in the Pleiades, a practice which was also used in historical Europe, especially in Greece.

The Native American tribe, the Kiowa, had a myth similar to the Lakota that explained the creation of the Pleiades. According to the Kiowa there were seven young maidens that went out to play and were spotted by several giant bears. The bears saw the young women and began to chase them. In an effort to escape the bears the women climbed on top of a rock and prayed to the spirit of the rock to save them.

Hearing their prayers the rock began to rise from the ground towards the Heavens so that the bears couldn't reach the maidens. The seven women reached the sky and were then turned into the star constellation we know today. The bears in an effort to climb the rock left deep claw marks in the sides which had become too steep to climb.

The rock later became known as Devil's Tower which is located in the state of Wyoming.

In the ancient Andes, the Pleiades were associated with abundance, because they return to the Southern Hemisphere sky each year at harvest-time. In Quechua they are called collca', or storehouse.

Paul Goble, Native American storyteller, tells a Blackfoot legend that he says is told by other tribes as well. In the story, the Pleiades are orphans that were not cared for by the people, so they became stars. Sun Man is angered by the mistreatment of the children and punishes the people with a drought, until the dogs, the only friends of the orphans, intercede on behalf of the people.

The American Hopi Indians built their underground Kivas for multiple utilitarian uses. The most important of which was their ceremonial meeting place. The access was a ladder through a small hole in the roof of the round hole in the ground. During certain ceremonies, the night passage of the Pleiades over the center of the opening of the entrance hole was a direct signal to begin a certain ceremony.

Most of the cultures used the angle of the Pleiades in the night sky as a time telling device.

 

Ukrainian
In Ukrainian traditional folklore the Pleiades are known as Стожари (Stozhary), Волосожари (Volosozhary), or Баби-Звізди (Baby-Zvizdy).

'Stozhary' can be etymologically traced to "стожарня" (stozharnya) meaning a 'granary', 'storehouse for hay and crops', or can also be reduced to the root "сто-жар", (sto-zhar) meaning 'hundredfold glowing'.

'Volosozhary' (the ones whose hair is glowing), or 'Baby-Zvizdy' (female-stars) refer to the female tribal deities. Accordingly to the legend, seven maids lived long ago. They used to dance the traditional round dances and sing the glorious songs to honor the gods. After their death the gods turned them into water nymphs, and, having taken them to the Heavens, settled them upon the seven stars, where they dance their round dances (symbolic for moving the time) to this day. (see article in Ukrainian Wikipedia)

In Ukraine this asterism was considered a female talisman until recent times.

 

Other cultures
The Subaru logo depicts the six stars of the Pleiades cluster that are usually visible from earth with the unaided eye (however it is possible to see many more than six stars under favorable conditions).

• In the Bible the Pleiades supposedly mentioned as Khima (Amos 5:8); Talmud (Berachot 58B) says that it has about 100 stars.

  

• In Japan, the Pleiades are known as 昴 Subaru, and have given their name to the car manufacturer whose logo incorporates six stars to represent the five smaller companies that merged into one. Subaru Telescope, located in Mauna Kea Observatory on Hawaii, is named after the Pleiades also.
   

• In Arabic the Pleiades are known as al-Thurayya الثريا, and mentioned in Islamic literature. The name was borrowed into Turkish as a female name, and is in use in both Turkey (as Surayya) and Arab countries (for example Thoraya Obaid). It is also the name of the Thuraya satellite phone system based in the United Arab Emirates.
   

• In Turkish they are known as Ülker.
   

• In the Persian language they are known as "Pervin".
   

• In Chinese constellations, they are 昴 mao, the Hairy Head of the white tiger of the West, while the name of the Hindu God Kartikeya means him of the Pleiades.
   

• In the Swahili language of East Africa they are called "kilimia" (Proto-Bantu *ki-dimida in Bantu areas E, F, G, J, L, and S) which comes from the verb -lima meaning "dig" or "cultivate" as their visibility was taken as a sign to prepare digging as the onset of the rain was near.
   

• In the closely related Sesotho language of the Southern Africa's Basotho people the Pleiades are called "Seleme se setshehadi" ("the female planter"). Its disappearance in April (the 10th month) and the appearance of the star Achernar signals the beginning of the cold season. Like many other Southern African cultures, Basotho associate its visibility with agriculture and plenty.
   

• In Western astrology they represent coping with sorrow and were considered a single one of the medieval fixed stars. As such, they are associated with quartz and fennel.
   

• In Indian astrology the Pleiades were known as the asterism (nakshatra) K'ttikā (which in Sanskrit is translated as "the cutters.") The Pleiades are called the star of fire, and their ruling deity is the Vedic god Agni, the god of the sacred fire. It is one of the most prominent of the nakshatras, and is associated with anger and stubbornness.

The word has acquired a meaning of "multitude", inspiring the name of the French literary movement La Pléiade and an earlier group of Alexandrian poets, the Alexandrian Pleiad.