Everything about Pleiades totally explained
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| names = M45, When studies were first made of the stars'
proper motions, it was found that they're 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. 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.
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 isn't 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 isn't yet known why the error occurred. The distance to the Pleiades is currently thought to be the higher value of about 135 parsecs (roughly 440 light years). 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 analyse brown dwarfs in the Pleiades and other young clusters, because they're 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 won't 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
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 isn't 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
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>
| Name |
Pronunciation (& ) |
Designation |
Apparent magnitude |
Stellar classification |
| Alcyone |
, al-sye'-ə-nee |
Eta (25) Tauri |
2.86 |
B7IIIe |
| Atlas |
, at'-ləs |
27 Tauri |
3.62 |
B8III |
| Electra |
, ee-lek'-trə |
17 Tauri |
3.70 |
B6IIIe |
| Maia |
; may'-ə, mye'-ə |
20 Tauri |
3.86 |
B7III |
| Merope |
, mair'-ə-pee |
23 Tauri |
4.17 |
B6IVev |
| Taygeta |
, tay-ij'-ə-tə |
19 Tauri |
4.29 |
B6V |
| Pleione |
, plye'-ə-nee |
28 (BU) Tauri |
5.09 (var.) |
B8IVep |
| Celaeno |
, sə-lee'-no |
16 Tauri |
5.44 |
B7IV |
| Asterope |
, ə-stair'-ə-pee |
21 and 22 Tauri |
5.64;6.41 |
B8Ve/B9V |
| — |
— |
18 Tauri |
5.65 |
B8V |
In folklore and literature
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.
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
Hawaiʻi known as Makaliʻi. 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 didn't 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's 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're 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
In the
Bible the Pleiades supposedly mentioned as Khima (Amos 5:8),
Talmud (Berachot 58B) says that it has about 100 stars.
In the Arab, Persian, and Turkic worlds, the Pleiades are referred to
Surayya/ (ثریا) and allegorically refer to something of beauty.
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 Turkish they're known as Ülker.
In Arabic the Pleiades are known as "Sureyya" and in Persian language they're known as "Pervin".
In
Chinese constellations, they're 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're 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're associated with
quartz and
fennel.
In
Indian astrology the Pleiades were known as the asterism (
nakshatra) (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.
Jehovah's Witnesses, for 62 years (1891 to 1953), believed the Pleiades cluster or more precisely the star Alcyone was the physical location of the eternal throne of God.
21 century significance
In
Ufology some believers describe human-like aliens (called
Pleiadeans) as originating from this system.
One image of the pleiades was selected for the cover art of the US release of Xexyz.
Further Information
Get more info on 'Pleiades'.
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