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The Pleiades (M45)

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Image of the Pleiades, provided by NASA and STScI.

The Pleiades open star cluster is one of the most identifiable celestial objects, even for the novice astronomer. Ancient depictions of the group still exist in caves in Lascaux, central France, and appear on the famed Nebra Sky Disc. The Pleiades appear in Homer's Odyssey and their 'sweet influence' is also mentioned in The Bible. They were well known to the ancient Greeks who gave them the name we know them by today, derived from their word peleiades meaning 'flock of doves'.

The Stars of the Pleiades

The Pleiades by Moonhogg.

Turning binoculars or a small telescope upon the Pleiades for the first time reveals its magnificence to the stunned viewer. The distance of an average of 440 light years1 seems crossed in an instant and you almost feel like you can reach out and touch them. They truly are a spectacular sight; for some astronomers this star grouping is their favourite celestial object, and a perfect starting point to test new equipment, as well as providing a point of reference for star-hopping.

Located in the constellation  Taurus, the Pleiades formed around 100 million years ago, when dinosaurs ruled the Earth. We can estimate its age because it contains hot blue stars, which are considered 'young'. The glittering cluster contains over 500 stars, and its main stars Alcyone, Merope, Celaeno, Electra, Asterope, Taygeta and Maia are easily spotted with the naked eye situated on the celestial bull's shoulder.

The scientific star names are simple to understand (if you know your Greek alphabet). For example: the 'alpha' star means it is the brightest star in that constellation. The next brightest is designated 'beta' etc. Combined with the genitive form of the constellation, this is known as the 'Bayer designation'. Some stars have proper names as well, for example, alpha Tauri is Aldebaran. Most of the rest have Flamsteed numbers; that is a number plus the genitive form of the constellation like 17 Tauri: this system was introduced by the first Astronomer Royal, John Flamsteed. Variable stars are given English capital letters plus the constellation genitive, eg Pleione is classified BU Tauri as well as its original 28 Tauri.

Star NameDesignationStellar MagSpectral Type
Alcyoneeta Tauri2.8 varMultiple system
Asterope21/22 Tauri5.6/6.4Binary system
Celaeno16 Tauri5.4Blue-white dwarf
Electra17 Tauri3.7Blue-white sub-giant
Maia20 Tauri3.8Blue-white sub-giant
Merope23 Tauri4.2Blue-white dwarf
Taygeta19 Tauri4.3Blue-white dwarf
Atlas27 Tauri3.6 varTriple star system
Pleione28 Tauri/BU Tauri4.7 to 5.5 varBlue-white dwarf

Alcyone (eta Tauri)

Alcyone A, the main component of eta Tauri, is a blue-white giant about 1,400 times as luminous as the Sun, around 410 light years distant. Alcyone A has a circumstellar disc created by its exceptionally-fast rotation speed (+200km/s) and rate of mass loss. Its binary partner eta2 has the same stellar classification, that of blue-white giant, but its spin is more sedate. This pair of giants are orbited by two white dwarfs Alcyone B and C, the latter is a delta Scuti-type pulsating variable star. Completing the party is Alcyone D, a yellow-white main sequence dwarf. These types of stars are the targets of extrasolar planet searches due to their similarity with our own Sun.

Asterope

Asterope is actually a binary system comprising two blue-white main sequence dwarf stars. They have their own Flamsteed designations, namely 21 Tauri and 22 Tauri.

Atlas

Atlas is a circumfluent triple star system comprising a binary pair of blue-white stars which orbit each other, Atlas A, and a much more distant companion, Atlas B, which encompasses them both.

Pleione

Pleione is a rapidly-rotating blue-white dwarf designated 28 Tauri, and being a special type of variable star, it also bears the catalogue reference BU Tauri. Pleione is a gamma Cassiopeiae-type variable; that means that gamma Cassiopeiae was the prototype of this type of variable star, and others identified latterly are said to be of that type. American artist and amateur astronomer Chesley Bonestell  (1888 - 1986), the 'Father of Modern Space Art', painted his own interpretation of Pleione with a purple hue, hence its nickname 'Purple Pleione'.

Pre-history

In 1940 a reported 16,500-year-old map of the Pleiades star cluster was discovered on a cave wall at Lascaux in central France. Draped above the shoulder of a painted bull are markings which could represent the 'seven sisters'.

Around 17,000 years ago, this region of sky would never have set below the horizon and it would have been especially prominent at the start of spring. It is a map of the prehistoric cosmos. It was their sky, full of animals and spirit guides.
– Researcher Dr Michael Rappenglueck, University of Munich

The Nebra Sky Disc

The Nebra Sky Disc, supposedly depicting the Pleiades, dates from around 1600BC. A more in-depth discussion of the disc, said to be the oldest sky chart in the world, is explained in its own h2g2 Entry.

History

The rising of the Pleiades was considered a sign that the season for sailing had begun by ancient mariners, who believed a goddess protected sailors from storms. We know the Pleiades was recognised by early astronomers because Greek scholar Homer spoke of them to his students in 750BC, and wrote about them in the Odyssey and the Iliad. This is the earliest written mention of the Pleiades that we know of in history:

Sleep did not weigh on his eyelids as he watched the Pleiades, and late-setting Boötes, and the Bear.
– Homer (as Odysseus spread his sails out of Ogygia) taken from Homer's Odyssey.

The origin of the name is probably Greek: the word peleiades meaning 'flock of doves', appears in an ode written in the 5th Century BC by Greek poet Pindar, and seems quite befitting. Aeschylus, also in the 5th Century BC, describes them as 'wingless Peleiades' because 'they have the form of phantoms of the night'; literally translates to veiled stars.

For near the Pleiades, those mountain maids, needs must Orion follow close behind.
– Nemean Ode
by Greek poet Pindar

The Pleiades are mentioned in the Bible:

Canst thou bind the sweet influences of Pleiades, or loose the bands of Orion?
– The Bible: Book of Job, verse 38:31

The Ancient Romans referred to the Pleiades as 'The Bunch of Grapes'. Alcyone was called Al Jauz (the Walnut) by early Arabian astronomers.

The Clusterers

Around the fourth Century BC the Pleiades were referred to as 'The Clusterers', an individual constellation, by Greek astronomer Eudoxus of Knidos, and similarly a century later by his compatriot Aratos in his Phainomena (book of Astronomy).

Navajo Cosmology

The Diné (Navajo people) who lived in America before Christopher Columbus sailed across the Atlantic Ocean in 1492 AD and 'discovered' it had their own legends about the creation of the world and the relationship between Mother Earth and Father Sky. Their deity Black God placed the orderly Pleiades above the heads of his people as watchers; in effect they were his extra eyes. The rest of the stars in the night sky were strewn there haphazardly by Coyote the Trickster to confuse lost and wandering souls so that they might never find their way home.

Messier

French astronomer Charles Messier  (1730 - 1817), the 'comet ferret', identified the 'cluster of stars, known by the name of the Pleiades' on 4 March, 1769. He listed it as M45 in his famous catalogue of 'non-comets', Mémoires de l'Academie. Messier made further, more extensive studies of M45 in 1785, 1790, and 1796.

Von Mädler

German astronomer and selenographer Johann Heinrich von Mädler (1794 - 1874) believed that Alcyone was the centre of the Galaxy! He studied the heavens from Berlin, then moved to Estonia to take the post of director of the Dorpat Observatory. Von Mädler's conclusion about Alcyone was refuted by other astronomers; quite vehemently so by FGW Struve (1793 - 1864). Although he was incorrect in his assumptions about Alcyone, von Mädler was well respected in astronomy circles and his other work was lauded by his peers. An avid moon-watcher and mapper, von Mädler jointly produced, with Wilhelm Beer, the first accurate map of the Martian features.

The Bedford Catalogue

Admiral WH Smyth created his own Bedford Catalogue which was first published in 1844. As well as referencing over 600 binary and multiple star systems, the Bedford Catalogue features 170 nebulae and star clusters, including the Pleiades.

Thomas William Webb

The Rev TW Webb (1807 - 1885) compiled Celestial Objects for Common Telescopes, published in 1859. It includes a section on the Pleiades.

Barnard's Merope Nebula

IC 349 is a reflection nebula discovered by EE Barnard in 1890. Its close proximity to Merope is slowly destroying it; eventually there will be nothing left. Luckily for us, the Hubble Space Telescope was able to capture this fabulous image for our delectation now, and future generations to gaze in wonder at what used to be.

Collinder 42

Swedish astronomer Per Collinder (1890 - 1974) created his own catalogue of open star clusters. Collinder's list included the Pleiades at number 42.

The NGC and Other Designations

The New General Catalogue was compiled by John Louis Emil Dreyer, the director of the Armagh Observatory from 1882 to 1916. Dreyer did not list M45 as a specific NGC object, but some of the nebulae surrounding individual stars feature on the NGC: the Maia Nebula is NGC 1432, and the Merope Nebula is NGC 1435.

Other designations for the Pleiades are: the Seven Sisters, Collinder 42, Bode 8, Melotte 22, OCL 421, Lund 117.

Around the World

Mayan astronomers called the Pleiades Tzab-ek (tail of the rattlesnake). Their calendar, the Tzol'kin, was based on the cycle of the Pleiades. The Mayans believed Alcyone was the celestial home of the souls of their ancestors.

Ancient Egyptians had deities representing every part of their daily lives, as well as the divine ones charged with presiding over their death and afterlife. The Pleiades played an important role in their calendar and were said to represent the goddess Neith, who was their 'divine mother'. Neith had a temple in Lower Egypt called Per-bit, which translates as 'house of the bee', a reference to honey, which was a symbol of resurrection, and so highly prized that it was used as an offering to the gods.

  • The Chinese call them the 'Blossom Stars'
  • Their Persian name is Soraya
  • In Sanskrit they are called Krittikas (the wives of the seven rishis)
  • Their Japanese name is Subaru
  • In the Islamic religion they are known as At-thuraiya
  • Their Maori name is Matariki
  • Australian Aboriginal tribal members called them Kungkarungkara (ancestral women) and Makara (Orion's wives)
  • Their Hawaiian name is Makali'i

Native American Legend

A holy man approached the home of a baker who was preparing a batch of loaves to sell later that day. When the holy man said he was tired and hungry but had no money for food, the baker gave him bread and said 'No charge'. The baker's wife invited him to bathe and rest, and again, no payment was expected. The baker's seven daughters danced to entertain their guest. When the baker and his family had all completed their earthly lives, they were immortalised as the stars that form the Pleiades as a reward for their acts of kindness.

Mythology: The Seven Sisters

The Pleiades star cluster is also known as the 'Seven Sisters' – according to Greek mythology, they are the seven daughters of Atlas, the god who carried the heavens upon his shoulders, and Pleione2. The sisters Alcyone, Asterope, Celaeno, Electra, Maia, Merope and Taygeta are represented by seven of the brightest stars in the cluster. (Although according to one telling, one sister is 'wandering', 'hidden' or 'lost', but historically opinions differ on which one of the named stars is on walkabout.) Their parents Atlas and Pleione also have namesake stars in the Pleiades.

According to one version of the story, when the seven sisters complained that they were being pursued by Orion the hunter, the gods changed them into stars and they became the Pleiades. Another tells of their much-loved brother, Hyas, who was killed in a hunting accident. Their grief was so intense that they wept bitter tears and nothing could console them, so Zeus placed them (and their half-sisters the Hyades) in the heavens so they could weep for eternity.

The Sisters

Maia was the firstborn, and the shyest of all the siblings. Some folklore links Maia to presiding over springtime festivals, particularly the May Day one, whence came the tradition of dancing round the maypole, a fertility symbol. Other stories say Maia is the goddess of cave-dwellers, hermits and singletons. Maia had a liaison with Zeus, and their offspring was fleet-footed Hermes, who became the messenger of the gods. Maia was revered as a good mother figure, who in turn guards midwives and expectant mothers. The month of May was named in her honour. There is a Roman goddess of the same name, whose Feast Day is 15 May. This Maia is not so shy as her Greek counterpart, for she is the Roman goddess of sexuality!

Merope married King Sisyphos (or Sisyphus) of Ephyre (Corinth), a descendant of the famed Prometheus. Through their son Glaucus they founded the Corinthian race. Merope is one of the possibilities for the 'hidden' or 'missing' star, supposedly because of the shame she felt at having chosen a human for a mate. Merope had not lacked divine attention, she was actively pursued by the god Orion and was even Zeus' lover for a while, until he tired of her and moved on to her sister Electra.

Electra bore Zeus a son, the demigod Dardanus, who was the founder and first king of Troy. Electra married King Corythus of Tuscia, who was also a son of Zeus. Their son Iason impregnated Demeter, the goddess of the Earth, which so annoyed Zeus3 that in his anger he hurled a thunderbolt at Iason, killing him instantly. Dardanus also died before his mother, and Electra's grief was so great at the loss of both her sons that she wore a veil forevermore.

Celaeno married Poseidon, god of earthquakes and the sea. Their son Lycos was joint ruler of the paradise called the Isles of the Blessed, also known as the Fortunate Isles and the Elysian Fields, with some writers equating them to fabled Atlantis. Poseidon also consorted with his sister-in-law, Alcyone.

Alcyone was the mother of Aethusa, beloved of Apollo, and twin sons Hyrieus and Hyperenor by Poseidon.

Taygeta (also spelled 'Taygete') was 'Mistress of the animals', a title bestowed by the goddess of the forest, Artemis, a daughter of Zeus. Taygeta was another prize fancied by Zeus. She spurned him, and invoked the protection of her guardian Artemis. The goddess could not defy her father Zeus, but neither could she ignore the plea of the maiden. So Artemis morphed the Pleiad into the form of a doe, her sacred animal. But the disguise didn't fool Zeus, who merely changed himself into a stag and coupled with her. Their offspring was Lacedæmon who became the founder of Sparta.

Asterope was loved by Ares, the god of war, and became the mother of Oenomaus, the king of Pisa, by him.

The Parents

Atlas was the Titan charged with the sacred duty of holding up the heavens, although he has tried to shirk this job occasionally. Knowing that not many possessed the strength for the task, he seemed destined to carry the burden alone, until Hercules requested his assistance for one of his 12 labours. Atlas eagerly agreed to perform a task in exchange for Hercules shouldering the heavens for a while, but Atlas enjoyed his freedom so much that he tried to trick Hercules into remaining. Pretending that he aquiesced, Hercules asked that he might pad his shoulder to ease the burden, and Atlas agreed. As soon as they'd completed the transfer, Hercules skedaddled to complete his labours.

Atlas must have had more time off than is recorded, as he managed to father several children in different families. Aside from the seven daughters with Pleione, there are the Hyades (five daughters and a son with Æthra) and the Hesperides (four daughters with Hesperius).

Pleione, an Oceanid, daughter of Tethys and the Titan Oceanus, was the mother of the Pleiades, which literally means 'the children of Pleione'.

Pleione is a subgenus of the orchid family, with many varieties including albiflora, aurita, formosana, forresitii, hubeiensis, limprichti, mazama, speciosa, versailles and vesuvius. Some new-coloured varieties are named after Purple Pleione eg: Pleione Brigadoon is light purple or violet which has a red and white frayed lip and yellow stamen, and Pleione Tongariro is imperial purple whose lip is frilled and streaked white with red and yellow splashes.

The Pleiades in Modern Culture

The Japanese know the Pleiades as Subaru, and the Japanese car firm of Subaru are named after it. Their 'manufacturers symbol' is a depiction of the cluster that you'll find on the front of all of their cars.

Pleiades by Iannis Xenakis  (1922 - 2001) is a dramatic work meant to portray 'clouds, nebulas and galaxies of the fragmented dust of beats organised by rhythm' according to the composer. The percussion piece, performed by members of the BBC Symphony Orchestra conducted by Martyn Brabbins, was featured during the 2008 Proms season.

The Ecliptic

Due to the fact that Taurus is a sign of the zodiac, its position on the ecliptic (the perceived passage of the Sun, the Moon and other planets of our Solar System) means that sometimes certain stunning alignments take place. This is always an exciting event for astronomers, for whom the night sky is a magnetic draw anyway, no matter how cold or sparse the viewing conditions.

The Moon

The Moon isn't large enough to cover the Pleiades entirely, but it can fit in the 'box' formed by four of the main stars. Usually an alignment between the Moon and something else is an event to be savoured, especially if it involves an occultation (when the Moon completely covers the other object) as these events are quite rare. However, the near-proximity of the Moon is not always a good thing. On close encounters with the Pleiades the brightness of the Moon's reflected sunlight can 'drown out' their attractiveness.

Take for example Astronomy Picture of the Day's featured image of 14 April, 2005. The prodigious crescent moon attracts full attention because it highlights the dynamics of the Sun-Earth-Moon alignment: the sawtooth edge of the crescent shape cutting across the Moon's face is due to the sunlight hitting mountains on the Moon's surface and casting shadows. The rest of the Moon is blocked by the Earth, but Earthshine means it is not in complete darkness. We're able to pick out some lunar features we'd not otherwise be able to see. The main stars of the Pleiades, to the right of the Moon, are barely noticeable in comparison to the hypnotic Moon.

Venus

The celestial hen-party of 'Venus in the Pleiades' makes quite a headline, guaranteed to attract attention. However, because Venus is so bright, it tends to overwhelm the glory of 'the sisters', but we do get a rare photo opportunity such as the one featured at Astronomy Picture of the Day in April 2004.

People can't feel Earth moving through its orbit, but this is an excellent opportunity for them to visually see the effects of planetary motion.
– NASA astrophysicist Dennis Gallagher

Image of the Pleiades provided by NASA and STScI. It is requested by STScI that in any subsequent use of this work NASA and STScI be given appropriate acknowledgement.

1A light year is the distance light travels in one year, roughly 5.88 trillion miles or 9.46 trillion km.2The Greek word pleiôn means 'plenty'.3Demeter was also Zeus' lover, with whom he fathered a daughter, Persephone, but that's another story.

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