Looking for the Pleiades

Pleiades large.jpgPleiades

Observation data
Constellation:Taurus
Right ascension:3h 47m 24s[1]
Declination:+24° 7′[1]
Distance:390–460 ly (120–140 pc)
 Other designations:M45, Seven Sisters, Melotte 22

Astronomy

In astronomy, the Pleiades or Seven Sisters (Messier object 45 or M45), is an open star cluster containing middle-aged hot B-type stars located in the large constellation of Taurus (Latin for bull, Taurus.svg). Taurus is one of the constellations of the zodiac, which means it is crossed by the plane of the ecliptic. It came to symbolize the bull in the mythologies of Ancient Babylon, Egypt and Greece. Taurus hosts two of the nearest open clusters to Earth, the Pleiades and the Hyades, both of which are visible to the naked eye.

The Pleiades is among the nearest star clusters to Earth and is the cluster most obvious to the naked eye in the night sky. The name Pleiades comes from Greek mythology; the celestial entity has several meanings in different cultures and traditions.

The cluster is dominated by hot blue and extremely luminous stars that 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 (hence the alternate name Maia Nebula after the star Maia), but is now known to be an unrelated dust cloud in the interstellar medium that the stars are currently passing through.

Computer simulations have shown that the Pleiades was probably formed from a compact configuration that resembled the Orion Nebula. Astronomers estimate that the cluster will survive for about another 250 million years, after which it will disperse due to gravitational interactions with its galactic neighborhood.

Observational history

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.

In Tamil culture this star cluster is attributed to Lord Murugan (Lord Murugan raised by the six sisters known as the Kārththikai Pengal and thus came to be known as Kārtikeyan). In Sanskrit he is known as Skanda. The Pleiades (Krittika) are particularly revered in Hindu mythology as the six mothers of the war god Murugan, who developed six faces, one for each of them.

The Babylonian star catalogues name the Pleiades MUL.MUL or “star of stars”, and they head the list of stars along the ecliptic, reflecting the fact that they were close to the point of vernal equinox around the 23rd century BC.
 
The earliest known depiction of the Pleiades is likely a bronze age artifact known as the Nebra sky disk, dated to approximately 1600 BC. Some Greek astronomers considered them to be a distinct constellation, and they are mentioned by Hesiod, and in Homer’s Iliad and Odyssey. The rising of the Pleiades is mentioned in the Ancient Greek text Geoponica. The Greeks oriented the Hecatompedon temple of 1150 BC and the Parthenon of 438 BC to their rising.
 
They are also mentioned three times in the Bible (Job 9:9 and 38:31, as well as Amos 5:8). Some scholars of Islam suggested that the Pleiades (Ats-tsuraiya) are the Star in Najm, which is mentioned in the Quran.

In Japan, the constellation is mentioned under the name Mutsuraboshi (“six stars”) in the 8th century Kojiki and Manyosyu documents. The constellation is also known in Japan as Subaru (“unite”) and is depicted in the logo and name of the Subaru automobile company. The Persian equivalent is Parvin (pronounced Parveen).

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

Composition

The cluster core radius is about 8 light years and tidal radius is about 43 light years. The cluster contains over 1,000 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 cluster is slowly moving in the direction of the feet of what is currently the constellation of Orion.
 
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 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.

Brightest stars

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

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

 
Pleiades Bright Stars
Name Pronunciation (IPA & respelling) Designation Apparent magnitude Stellar classification
Alcyone /ælˈsaɪ.əniː/ al-SY-ə-nee Eta (25) Tauri 2.86 B7IIIe
Atlas /ˈætləs/ AT-ləs 27 Tauri 3.62 B8III
Electra /ɨˈlɛktrə/ i-LEK-trə 17 Tauri 3.70 B6IIIe
Maia /ˈmeɪə/, /ˈmaɪə/ MAY, MY 20 Tauri 3.86 B7III
Merope /ˈmɛrəpiː/ MERR-ə-pee 23 Tauri 4.17 B6IVev
Taygeta /teɪˈɪdʒɨtə/ tay-IJ-i-tə 19 Tauri 4.29 B6V
Pleione /ˈplaɪ.əniː/ PLY-ə-nee 28 (BU) Tauri 5.09 (var.) B8IVpe
Celaeno /sɨˈliːnoʊ/ sə-LEE-noh 16 Tauri 5.44 B7IV
Sterope, Asterope /ˈstɛrɵpiː/, /əˈstɛrɵpiː/ (ə)-STERR-ə-pee 21 and 22 Tauri 5.64;6.41 B8Ve/B9V
18 Tauri 5.65 B8V

Source: https://en.wikipedia.org/wiki/Pleaides

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3 thoughts on “Looking for the Pleiades

  1. Julianne Victoria June 30, 2013 at 4:16 pm Reply

    Do you have some sort of star map or astrolabe to help you determine which stars you are looking at?

    • thesevenminds June 30, 2013 at 9:51 pm

      This will take some work. The stars will be out tonight, so I will draw a map and then try to match it to online maps. The other way around is just not going to work out.

    • Julianne Victoria June 30, 2013 at 10:15 pm

      Sounds like fun actually. 😉 Good luck!

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