Pleiades (astronomy)
The Pleiades or The Seven Sisters (Messier 45 or M45) is an open star cluster containing hot stars of spectral type B, of young age, located in the constellation of Taurus. It is among the closest star clusters to Earth, and is the cluster best visible to the naked eye in the night sky. The Pleiades hold a prominent place in ancient mythology, as well as a diversity of meanings in different cultures and traditions.
The cluster is dominated by extremely blue and luminous hot stars that have formed in the last 120 million years. The dust that forms a faint reflection nebulosity around the brightest stars was originally thought to have come from a breakup of the cluster formation itself (hence the alternative name for Maia nebula instead of star Maia), but it is now known to be an unrelated dust cloud in the interstellar medium, through which the stars are currently passing. And the above is based on the different values obtained from the radial velocity of the Pleiades, and the radial velocity of the nebula that seems to surround them. Computer simulations have shown that the Pleiades probably formed from a compact configuration resembling the Orion Nebula. Astronomers estimate that the group will survive for approximately another 250 million years, after which time it will disperse due to gravitational interactions in its galactic-like environment.
Distance
The distance to the cluster has been estimated by many methods, as it is an important step in calibrating distances in the universe. Knowing the exact distance to the Pleiades allows astronomers to draw a Hertzsprung-Russell diagram to estimate the distance to other clusters. Other methods can then extend the distance scale from open clusters to galaxies and later to clusters of galaxies, allowing a cosmic distance scale to be constructed.
Pre-launch results from the Hipparcos satellite found the Pleiades to be approximately 135 parsecs (440 light-years) from Earth. Hipparcos caused a stir among astronomers by finding a distance of only 118 parsecs (384.7 light-years) by measuring the parallax of some stars in the cluster, a technique that should yield the most direct and accurate results. More recent work has found that the distance calculated by Hipparcos was in error, although the cause of this error is unknown. The specific distance of the Pleiades is still unknown, but the true distance is currently thought to be around 136.2±1.2 parsec or 444 light-years.
It is the fourth closest open cluster to Earth.
Composition
The cluster is about twelve light-years across and contains a total of about 500 to 1,000 stars. It is dominated by young blue stars, eight of which can be seen with the naked eye depending on atmospheric conditions (very clear skies and no Moon): Taygeta (4.29), Pleione (5.05), Merope (4, 14), Maia (3.87), Electra (3.72), Celaeno (5.45), Atlas (3.62) and Alcyone (2.85). The numbers in parentheses indicate their magnitude of apparent brightness.
The order of its brightest stars is similar to that of Ursa Major and Ursa Minor, with a total mass estimated at about 800 solar masses.
The cluster is largely made up of brown dwarfs—objects with less than 8% of the solar mass—that are too light to be stars. These objects may make up about 25% of the cluster's total population, despite only contributing 2% of its total mass. Also present in the cluster are white dwarfs, which contradict the estimated age of the cluster. Due to the young age of the cluster, it is not expected that normal stars could have evolved to become white dwarfs. It is believed that rather than being individual stars of low or medium mass, the progenitors of these stars were massive and orbited in binary systems. During its rapid evolution, mass transfer from the more massive star to its companion may have accelerated its evolution towards a white dwarf.
Future
It has been calculated that the Pleiades have a future of only another 250 million years (Kenneth Glyn Jones); by then, they will have been separated as single (or multiple) stars along their path.
Under ideal observing conditions, some traces of nebulosity can be seen, and this is demonstrated in long-exposure photographs. It is a reflection nebula, caused by dust that reflects the blue light of hot, young stars.
This dust is often thought to have been left over from the formation of the cluster, but with an age of around 120 million years—which is generally the most widely accepted for this cluster—nearly all of the dust originally present would have been scattered by radiation pressure. The cluster appears to be passing through a particularly dusty region of the interstellar medium.
Studies show that the dust responsible for the nebulosity is not evenly distributed, but is mainly concentrated in two layers along the visible part of the cluster. These layers may have been formed by the slowing down due to radiation pressure as dust has moved towards the stars. The major stars are, in order of magnitude:
Alcyone, Atlas, Electra, Maia, Merope, Taygeta, Pleione, Celaeno, 21 Tauri (5.75) and 22 Tauri (6.40).
Literary mentions
The Pleiades are mentioned in several ancient scriptures.
The Iliad
In canto XVIII of the Iliad (483-489), Homer describes how Hephaestus, the god of fire and metallurgy, makes a shield for the battle of the hero Achilles in the Trojan War. On this shield he "engraved many artistic figures [...] the stars that crown the sky, the Pleiades, the Hyades, the robust Orion, and the Bear."
On Hesiod
In the work Works and days, by Hesiod, in the proem to the farmer's calendar it is mentioned (385):
As the Pléyades descendant of Atlas emerge,the harvest begins; and the openness when they hide.
and again when the year is completed they begin to appear when the sickle is sharpened.
From that moment they are hidden forty nights and forty days
The Bible
They appear three times in the Bible (Job 9:9; Job 38:31; and Amos 5:8).
In some versions of the Bible (Septuagint), the Pleiades are called Kima; however the Vulgate incorrectly identifies that name with the star Arthur.
In the Mahabharata
In the Majabhárata (an epicoreligious text from the 3rd century BC) they are mentioned as the six krittikas, which are the nymphs who raised the god Kartikeia.
The Popol Vuh
They are also mentioned in the Popol Vuh (the sacred book of the Mayans) under the name of Motz, which means "heap" and that they originated when Zipacná the Proud killed 400 warriors, whose Souls were taken by Gucumatz, the great heart of heaven, and placed as stars in the sky, thus creating the Pleiades.
Don Quixote
In more recent but no less important works, such as Don Quixote de la Mancha, mention is also made of "the seven goats", specifically Sancho speaks of them in chapter XLI of the second part, when he talks about air travel What Don Quixote and he did about Clavileño:
And it happened that we were going on the part where the seven goons are, and in God and in my soul that as I was in my childhood I was in my pissed land, that just as I saw them, he gave me a win of entertaining me with them for a while, that if I did not fulfill it, it seems to me to burst.
Other cultures
The Mayans
The Maya based their Haab civil calendar on the annual cycle of the Pleiades, and believed it to be the place of origin of their culture. They are called Tzab-ek or rattlesnake tail, and are also known as the seven sisters.
The Aztecs
The Aztecs knew the Pleiades as Tianquiztli "the market", this because of the crowds that used to form in the markets and their resemblance to the stars of this constellation.
The Rarámuri
The Rarámuri call them the “welia” which literally translates as the many. «Welia be aniriame so'pod, a mu machi? chi'rimeachi ma'china» (The stars called The Many, do you know them? They come out at dawn)
The Incas
According to Aveni, the heliacal rise of the Pleiades begins the Inca year, which occurs thirteen to fifteen days before the winter solstice. They saw a relationship between the time the Pleiades are visible and the annual agricultural cycle. Thus, one of the names given to the cluster was Qollqa, which means "food store" in Quechua. The Pleiades are absent from the night sky between May 3 and June 9, for a period of 37 days., which coincides with the interval between harvest and the next planting season in the highlands.
Although in reality the Inca Andean New Year begins in the month of August, which is still celebrated to date. Unlike the Aymara New Year, which is celebrated in mid-June.
Mapuche people
Possibly, the open star cluster of the Pleiades is the only celestial body in Charles Messier's catalog that was very well known to the Mapuche people. They called the Pleiades Gul Poñu ("lot of potatoes"), and depending on the appearance they presented during the early morning of the night of the Mapuche New Year or We Tripantu, they became an accurate meteorological indicator. If the Pleiades looked bright and clear, the southern winter that was beginning would not be so rainy, but if they were perceived leaden and diffuse, that heralded the arrival of a southern winter with a lot of rain on the coast and snow in the Chilean mountain range.
Spiritually, for the Mapuche, the energy that comes from the Pleiades gives women inner strength.[citation required]
The Rapanui
The Rapanui ―inhabitants of Easter Island― called the Pleiades «Matariki», which allowed them to determine the start of the new year and start festivals and ceremonies, and was possibly key in the Polynesian colonization of the island when used as a navigation guide.
Japan
In Japan, the constellation is mentioned under the name Mutsuraboshi ("six stars") in the 18th-century Kojiki VIII. Unlike Greek or Mayan mythology, Japan took only 6 of the 7 stars we know as the Pleiades since it is difficult to see the star of Merope with the naked eye. The constellation is now known in Japan as Subaru ("unite"). It was chosen as the brand name for Subaru automobiles to reflect the company's origins as a union of five companies, and is represented in the company's six-star logo; in the logo of Subaru vehicles the seventh star is missing, because it is represented by the car that bears the logo. The Subaru Telescope, located at the Mauna Kea Observatory in Hawaii, also bears the Japanese name for the Pleiades.
European description
On March 4, 1769, Charles Messier included them as number 45 in his first list of nebulae and star clusters, which was published in 1771.
Paraguay
In Paraguay the cumulus is also known as «the seven goats», very widespread in the folklore of that country thanks to the poem in Guaraní by Francisco Martín Barrios, which later served as the lyrics of the song to which Mauricio Cardozo Ocampo put music. In addition, it is their mythology, the seven cabrillas represent the end of the curse that Tau and Keraná had, the legend says that when Luisón was born (seventh myth of Paraguay), in the dark skies these stars shone alerting the Guarani that the curse of Tau and Kerana had finished.
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