Pleiades (star cluster)

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The Pleiades (also known as M45, or the Seven Sisters) is an open cluster in the constellation of Taurus. It is among the nearest to earth of all open clusters, probably the best known and certainly the most striking to the naked eye.

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General information

The Pleiades are about 450 Light years away from earth and were formed approximately 100 million years ago. There are approximately 500 stars in total in the cluster, but 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 the Plough and Ursa Minor (the Little Dipper).

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 left over from star formation reflecting the blue light of the hot young stars.

Like most open clusters, the Pleiades will not stay gravitationally bound forever, as the component stars are moving faster than the escape velocity of the cluster. Calculations suggest that the cluster will take about 250 million years to disperse.

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Names and technical information

The 9 brightest stars of the Pleiades are named for the Seven Sisters of Greek mythology (Asterope, Merope, Electra, Maia, Taygete, Celaeno and Alcyone) and their parents Atlas and Pleione. The Hyades were sisters of the Pleiades. The following table gives details of these stars:

**Pleiades Bright Stars**
Name	Designation	m	Type	Catalog
Alcyone	eta (25) Tauri	2.86	B7e III	vdB 23
Atlas	27 Tauri	3.62	B8 III	Ced 190
Electra	17 Tauri	3.70	B6e III	vdB 20
Maia	20 Tauri	3.86	B7 III	NGC 1432
Merope	23 Tauri	4.17	B6 IV	NGC 1435, IC 349
Taygeta	19 Tauri	4.29	B6 V	Ced 19e
Pleione	BU (28) Tauri	5.09 (var.)	B8e p	Ced 19p
Celaeno	16 Tauri	5.44	B7 IV	Ced 19c
Asterope	21 and 22 Tauri	5.64/6.41	B8e V/B9 V

m: visual magnitude

Catalog: catalog number of associated nebulosity

The name of the cluster itself has uncertain etymology, with suggested origins being from plein, to sail, making the Pleiades the 'sailing ones'; from pleos, full or many; or from pelaiades, flock of doves (in the Greek legend, the sisters are transformed into birds).

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The Pleiades in folklore

The Pleiades' high visibility in the night sky has guaranteed it a special place in many cultures, antique and modern:

To the Vikings, they were Freya's hens.
To the Maori of New Zealand, the Pleiades are called Mataariki and their heliacal rising signifies the beginning of the new year (around June).
The Australian Aborigines believed they were a woman who had been nearly raped by Kidili, the man in the moon. Alternatively, they were seven sisters called the Makara.
It is said that the Native Americans measured keenness of vision by the number of stars the viewer could see in the Pleiades. Even in historical Europe, especially in Greek circles, the Pleiades were a common vision test.
In Japan, the Pleiades are known as Subaru. The Subaru car company uses the Pleiades as their logo.

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External links and references

Ovid XIII, 293.
, SEDS Messier pages
Subaru


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