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74-457: Star clusters visible to the naked eye include the Pleiades , Hyades , and 47 Tucanae . Open clusters are very different from globular clusters. Unlike the spherically distributed globulars, they are confined to the galactic plane , and are almost always found within spiral arms . They are generally young objects, up to a few tens of millions of years old, with a few rare exceptions as old as

148-411: A Hertzsprung–Russell diagram for the cluster, which, when compared with those plotted for clusters whose distance is not known, allows their distances to be estimated. Other methods may then extend the distance scale from open clusters to galaxies and clusters of galaxies, and a cosmic distance ladder may be constructed. Ultimately astronomers' understanding of the age and future evolution of the universe

222-448: A torsion balance . The value he obtained differs by only 1% from the modern value, but was not as precise. The diurnal parallax of the Sun was accurately measured during the transits of Venus in 1761 and 1769, yielding a value of 9″ (9  arcseconds , compared to the present value of 8.794 148 ″ ). From the value of the diurnal parallax, one can determine the distance to the Sun from

296-401: A bow and a quiver. As noted by scholar Stith Thompson , the constellation was "nearly always imagined" as a group of seven sisters, and their myths explain why there are only six. Some scientists suggest that these may come from observations back when Pleione was farther from Atlas and more visible as a separate star as far back as 100,000 BC. In Japan , the cluster is mentioned under

370-625: A distinct constellation , and they are mentioned by Hesiod 's Works and Days , Homer 's Iliad and Odyssey , and the Geoponica . The Pleiades was the most well-known "star" among pre-Islamic Arabs and so often referred to simply as "the Star" ( an-Najm ; النجم ). Some scholars of Islam suggested that the Pleiades are the "star" mentioned in Surah An-Najm ("The Star") in

444-465: A few billion years, such as Messier 67 (the closest and most observed old open cluster) for example. They form H II regions such as the Orion Nebula . Open clusters typically have a few hundred members and are located in an area up to 30 light-years across. Being much less densely populated than globular clusters, they are much less tightly gravitationally bound, and over time, are disrupted by

518-481: A few hundred million years younger than the universe itself – which are mostly yellow and red, with masses less than two solar masses . Such stars predominate within clusters because hotter and more massive stars have exploded as supernovae , or evolved through planetary nebula phases to end as white dwarfs . Yet a few rare blue stars exist in globulars, thought to be formed by stellar mergers in their dense inner regions; these stars are known as blue stragglers . In

592-529: A few tens of millions of years, open clusters tend to have dispersed before these stars die. A subset of open clusters constitute a binary or aggregate cluster. New research indicates Messier 25 may constitute a ternary star cluster together with NGC 6716 and Collinder 394. Establishing precise distances to open clusters enables the calibration of the period-luminosity relationship shown by Cepheids variable stars , which are then used as standard candles . Cepheids are luminous and can be used to establish both

666-454: A map of 64 stars of the Pleiades from his observations in 1779, which he published in 1786. The distance to the Pleiades can be used as a key first step to calibrate the cosmic distance ladder . As the cluster is relatively close to the Earth, the distance should be relatively easy to measure and has been estimated by many methods. Accurate knowledge of the distance allows astronomers to plot

740-441: A mythical mother, Pleione , effectively meaning "daughters of Pleione". In reality, the ancient name of the star cluster related to sailing almost certainly came first in the culture, naming of a relationship to the sister deities followed, and eventually appearing in later myths, to interpret the group name, a mother, Pleione. The M45 group played an important role in ancient times for the establishment of many calendars thanks to

814-440: A ringlike distribution around the centres of their host galaxies. As the latter they seem to be old objects. Star clusters are important in many areas of astronomy. The reason behind this is that almost all the stars in old clusters were born at roughly the same time. Various properties of all the stars in a cluster are a function only of mass, and so stellar evolution theories rely on observations of open and globular clusters. This

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888-497: A similar number to globular clusters. The clusters also share other characteristics with globular clusters, e.g. the stellar populations and metallicity. What distinguishes them from the globular clusters is that they are much larger – several hundred light-years across – and hundreds of times less dense. The distances between the stars are thus much greater. The clusters have properties intermediate between globular clusters and dwarf spheroidal galaxies . How these clusters are formed

962-677: A star cluster. Most young embedded clusters disperse shortly after the end of star formation. The open clusters found in the Galaxy are former embedded clusters that were able to survive early cluster evolution. However, nearly all freely floating stars, including the Sun , were originally born into embedded clusters that disintegrated. Globular clusters are roughly spherical groupings of from 10 thousand to several million stars packed into regions of from 10 to 30  light-years across. They commonly consist of very old Population II stars – just

1036-468: A thousand. A few of the brightest globular clusters are visible to the naked eye ; the brightest, Omega Centauri , was observed in antiquity and catalogued as a star, before the telescopic age. The brightest globular cluster in the northern hemisphere is M13 in the constellation of Hercules . Super star clusters are very large regions of recent star formation, and are thought to be the precursors of globular clusters. Examples include Westerlund 1 in

1110-536: Is a result of uncertainties in stellar evolution models, which include factors such as convective overshoot , in which a convective zone within a star penetrates an otherwise non-convective zone, resulting 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. Brown dwarfs can retain their lithium, however. Due to lithium's very low ignition temperature of 2.5 × 10 K,

1184-605: Is also evident in northern Europe. The Pleiades cluster is displayed on the Nebra sky disc that was found in Germany and is dated to around 1600 BC. On the disk the cluster is represented in a high position between the Sun and the Moon. This asterism also marks the beginning of several ancient calendars: Although M45 is no longer at the vernal point, the asterism still remains important, both functionally and symbolically. In addition to

1258-474: Is approximately equal to the mass of the Sun . It is often used to indicate the masses of other stars , as well as stellar clusters , nebulae , galaxies and black holes . More precisely, the mass of the Sun is The solar mass is about 333 000 times the mass of Earth ( M E ), or 1047 times the mass of Jupiter ( M J ). The value of the gravitational constant was first derived from measurements that were made by Henry Cavendish in 1798 with

1332-410: Is converted into helium through nuclear fusion , in particular the p–p chain , and this reaction converts some mass into energy in the form of gamma ray photons. Most of this energy eventually radiates away from the Sun. Second, high-energy protons and electrons in the atmosphere of the Sun are ejected directly into outer space as the solar wind and coronal mass ejections . The original mass of

1406-461: Is difficult to measure and is only known with limited accuracy ( see Cavendish experiment ). The value of G times the mass of an object, called the standard gravitational parameter , is known for the Sun and several planets to a much higher accuracy than G alone. As a result, the solar mass is used as the standard mass in the astronomical system of units . The Sun is losing mass because of fusion reactions occurring within its core, leading to

1480-413: Is dominated by fainter and redder stars . An estimate of the frequency of binary stars in the Pleiades is approximately 57%. The cluster contains many brown dwarfs , such as Teide 1 . These are objects with less than approximately 8% of the Sun 's mass, insufficient for nuclear fusion reactions to start in their cores and become proper stars. They may constitute up to 25% of the total population of

1554-512: Is influenced by their knowledge of the distance to the Pleiades. Yet some authors argue that the controversy over the distance to the Pleiades discussed below is a red herring , since the cosmic distance ladder can (presently) rely on a suite of other nearby clusters where consensus exists regarding the distances as established by the Hipparcos satellite and independent means (e.g., the Hyades ,

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1628-404: Is not to change, even if subsequent measurements improve on the location of the cluster centre. The first of such designations were assigned by Gosta Lynga in 1982. Pleiades The Pleiades ( / ˈ p l iː . ə d iː z , ˈ p l eɪ -, ˈ p l aɪ -/ ), also known as Seven Sisters and Messier 45 , is an asterism of an open star cluster containing young B-type stars in

1702-587: Is not yet known, but their formation might well be related to that of globular clusters. Why M31 has such clusters, while the Milky Way has not, is not yet known. It is also unknown if any other galaxy contains this kind of clusters, but it would be very unlikely that M31 is the sole galaxy with extended clusters. Another type of cluster are faint fuzzies which so far have only been found in lenticular galaxies like NGC 1023 and NGC 3384 . They are characterized by their large size compared to globular clusters and

1776-483: Is primarily true for old globular clusters. In the case of young (age < 1Gyr) and intermediate-age (1 < age < 5 Gyr), factors such as age, mass, chemical compositions may also play vital roles. Based on their ages, star clusters can reveal a lot of information about their host galaxies. For example, star clusters residing in the Magellanic Clouds can provide essential information about the formation of

1850-923: The Arabs (who call them al-Thurayyā ; الثريا ); the Chinese (who called them mǎo ; 昴 ); the Quechua (who call them Qullqa or the storehouse); the Japanese (who call them Subaru ; 昴 , スバル ); the Maya ; the Aztec ; the Sioux ; the Kiowa ; and the Cherokee . In Hinduism , the Pleiades are known as Kṛttikā and are scripturally associated with the war deity Kartikeya and are also identified or associated with

1924-532: The Coma Berenices cluster , etc.). Measurements of the distance have elicited much controversy. Results prior to the launch of the Hipparcos satellite generally found that the Pleiades were approximately 135 parsecs (pc) away from Earth. Data from Hipparcos yielded a surprising result, namely a distance of only 118 pc, by measuring the parallax of stars in the cluster—a technique that should yield

1998-466: The Hyades were sisters of the Pleiades. The following table gives details of the brightest stars in the cluster: Ages for star clusters may be estimated by comparing the Hertzsprung–Russell diagram for the cluster with theoretical models of stellar evolution . Using this technique, ages for the Pleiades of between 75 and 150 million years have been estimated. The wide spread in estimated ages

2072-551: The International Astronomical Union 's 17th general assembly recommended that newly discovered star clusters, open or globular, within the Galaxy have designations following the convention "Chhmm±ddd", always beginning with the prefix C , where h , m , and d represent the approximate coordinates of the cluster centre in hours and minutes of right ascension , and degrees of declination , respectively, with leading zeros. The designation, once assigned,

2146-679: The Milky Way , star clouds show through gaps between dust clouds of the Great Rift , allowing deeper views along our particular line of sight. Star clouds have also been identified in other nearby galaxies. Examples of star clouds include the Large Sagittarius Star Cloud , Small Sagittarius Star Cloud , Scutum Star Cloud, Cygnus Star Cloud, Norma Star Cloud, and NGC 206 in the Andromeda Galaxy . In 1979,

2220-518: The Quran . On numerous cylinder seals from the beginning of the first millennium BC, M45 is represented by seven points, while the Seven Gods appear, on low-reliefs of Neo-Assyrian royal palaces, wearing long open robes and large cylindrical headdresses surmounted by short feathers and adorned with three frontal rows of horns and a crown of feathers, while carrying both an ax and a knife, as well as

2294-530: The Saptamatrika(s) (Seven Mothers). Hindus celebrate the first day (new moon) of the month of Kartik as Diwali , a festival of abundance and lamps. The Pleiades are also mentioned three times in the Bible . The earliest known depiction of the Pleiades is likely a Northern German Bronze Age artifact known as the Nebra sky disk , dated to approximately 1600 BC. The Babylonian star catalogues name

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2368-559: The Spitzer Space Telescope and Gemini North telescope , astronomers discovered that one of the stars in the cluster, HD 23514 , which has a mass and luminosity a bit greater than that of the Sun, is surrounded by an extraordinary number of hot dust particles. This could be evidence for planet formation around HD 23514. Solar mass The solar mass ( M ☉ ) is a standard unit of mass in astronomy , equal to approximately 2 × 10   kg . It

2442-400: The asymptotic giant branch , before peaking at a rate of 10 to 10 M ☉ /year as the Sun generates a planetary nebula . By the time the Sun becomes a degenerate white dwarf , it will have lost 46% of its starting mass. The mass of the Sun has been decreasing since the time it formed. This occurs through two processes in nearly equal amounts. First, in the Sun's core , hydrogen

2516-668: The luminosity axis. Then, when similar diagram is plotted for a cluster whose distance is not known, the position of the main sequence can be compared to that of the first cluster and the distance estimated. This process is known as main-sequence fitting. Reddening and stellar populations must be accounted for when using this method. Nearly all stars in the Galactic field, including the Sun, were initially born in regions with embedded clusters that disintegrated. This means that properties of stars and planetary systems may have been affected by early clustered environments. This appears to be

2590-455: The proper motions of the stars, it was found that they are 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

2664-769: The weighted mean ; they gave a Hipparcos parallax distance of 126 pc and photometric distance of 132 pc based on stars in the AB Doradus , Tucana-Horologium and Beta Pictoris moving groups, which are all similar in age and composition to the Pleiades. Those authors note that the difference between these results may be attributed to random error. More recent results using very-long-baseline interferometry (VLBI) (August 2014), and preliminary solutions using Gaia Data Release 1 (September 2016) and Gaia Data Release 2 (August 2018), determine distances of 136.2 ± 1.2 pc, 134 ± 6 pc and 136.2 ± 5.0 pc, respectively. The Gaia Data Release 1 team were cautious about their result, and

2738-557: The Ecliptic . The name, Pleiades, comes from Ancient Greek : Πλειάδες . It probably derives from plein ("to sail") because of the cluster's importance in delimiting the sailing season in the Mediterranean Sea : "the season of navigation began with their heliacal rising ". In Classical Greek mythology the name was used for seven divine sisters called the Pleiades . In time, the name was said to be derived from that of

2812-563: The Magellanic Clouds dwarf galaxies. This, in turn, can help us understand many astrophysical processes happening in our own Milky Way Galaxy. These clusters, especially the young ones can explain the star formation process that might have happened in our Milky Way Galaxy. Clusters are also a crucial step in determining the distance scale of the universe . A few of the nearest clusters are close enough for their distances to be measured using parallax . A Hertzsprung–Russell diagram can be plotted for these clusters which has absolute values known on

2886-528: The Milky Way galaxy, globular clusters are distributed roughly spherically in the galactic halo , around the Galactic Center , orbiting the center in highly elliptical orbits . In 1917, the astronomer Harlow Shapley made the first respectable estimate of the Sun's distance from the Galactic Center, based on the distribution of globular clusters. Until the mid-1990s, globular clusters were

2960-506: The Milky Way. In 2005, astronomers discovered a new type of star cluster in the Andromeda Galaxy, which is, in several ways, very similar to globular clusters although less dense. No such clusters (which also known as extended globular clusters ) are known in the Milky Way. The three discovered in Andromeda Galaxy are M31WFS C1 M31WFS C2 , and M31WFS C3 . These new-found star clusters contain hundreds of thousands of stars,

3034-690: The Moon , i.e. five times the path that the "Moon" travels on average in one day and one night, to use the terminology of Abd al-Rahman al-Sufi . In Turkic Mythology - The Pleiades Constellation is one of the oldest cosmological figures of the Turks. Seasonal cycles in Anatolia are determined by this star group. The Pleiades are a prominent sight in winter in the Northern Hemisphere , and are easily visible from mid-southern latitudes. They have been known since antiquity to cultures all around

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3108-565: The Pleiades MUL ( 𒀯𒀯 ), meaning "stars" (literally "star star"), and they head the list of stars along the ecliptic, reflecting the fact that they were close to the point of the vernal equinox around the twenty-third century BC. The Ancient Egyptians may have used the names "Followers" and "Ennead" in the prognosis texts of the Calendar of Lucky and Unlucky Days of papyrus Cairo 86637. Some Greek astronomers considered them to be

3182-461: The Pleiades has been noted as curious, as most of Messier's objects were much fainter and more easily confused with comets—something that 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 the number on his list. Edme-Sébastien Jeaurat then drew in 1782

3256-503: The Pleiades showing 36 stars, in his treatise Sidereus Nuncius in March 1610. The Pleiades have long been known to be a physically related group of stars rather than any chance alignment. John Michell calculated in 1767 that the probability of a chance alignment of so many bright stars was only 1 in 500,000, and so surmised that the Pleiades and many other clusters must consist of physically related stars. When studies were first made of

3330-458: The Pleiades were probably formed from a compact configuration that once resembled the Orion Nebula . Astronomers estimate that the cluster will survive for approximately another 250 million years, after which the clustering will be lost due to gravitational interactions with the galactic neighborhood. Together with the open star cluster of the Hyades , the Pleiades form the Golden Gate of

3404-477: The Sun at the time it reached the main sequence remains uncertain. The early Sun had much higher mass-loss rates than at present, and it may have lost anywhere from 1–7% of its natal mass over the course of its main-sequence lifetime. One solar mass, M ☉ , can be converted to related units: It is also frequently useful in general relativity to express mass in units of length or time. The solar mass parameter ( G · M ☉ ), as listed by

3478-545: The VLBI authors assert "that the Hipparcos -measured distance to the Pleiades cluster is in error". The most recent distance estimate of the distance to the Pleiades based on the Gaia Data Release 3 is 135.74 ± 0.10 pc . The cluster core radius is approximately 8 light-years and tidal radius is approximately 43 light-years. The cluster contains more than 1,000 statistically confirmed members, not counting

3552-425: The case for our own Solar System , in which chemical abundances point to the effects of a supernova from a nearby star early in our Solar System's history. Technically not star clusters, star clouds are large groups of many stars within a galaxy , spread over very many light-years of space. Often they contain star clusters within them. The stars appear closely packed, but are not usually part of any structure. Within

3626-505: The cause of a great mystery in astronomy, as theories of stellar evolution gave ages for the oldest members of globular clusters that were greater than the estimated age of the universe. However, greatly improved distance measurements to globular clusters using the Hipparcos satellite and increasingly accurate measurements of the Hubble constant resolved the paradox, giving an age for the universe of about 13 billion years and an age for

3700-528: The changes in the calendars based on the lunar stations among the Indians and the Arabs, consider the case of an ancient Yemeni calendar in which the months are designated according to an astronomical criterion that caused it to be named Calendar of the Pleiades : the month of ḫams , literally "five", is that during which the Sun and al-Ṯurayyā , i.e. the Pleiades , deviate from each other by five movements of

3774-415: The cloud is depleted by star formation or dispersed through radiation pressure , stellar winds and outflows , or supernova explosions . In general less than 30% of cloud mass is converted to stars before the cloud is dispersed, but this fraction may be higher in particularly dense parts of the cloud. With the loss of mass in the cloud, the energy of the system is altered, often leading to the disruption of

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3848-541: The clouds begin to collapse and form stars . There is often ongoing star formation in these clusters, so embedded clusters may be home to various types of young stellar objects including protostars and pre-main-sequence stars . An example of an embedded cluster is the Trapezium Cluster in the Orion Nebula . In ρ Ophiuchi cloud (L1688) core region there is an embedded cluster. The embedded cluster phase may last for several million years, after which gas in

3922-431: 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 toward the stars. Analyzing deep-infrared images obtained by

3996-458: The cluster may be seen even with small telescopes or average binoculars. 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 approximately 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

4070-405: The cluster will take approximately 250 million years to disperse, because of gravitational interactions with giant molecular clouds and the spiral arms of our galaxy hastening its demise. With larger amateur telescopes, the nebulosity around some of the stars may be easily seen, especially when long-exposure photographs are taken. Under ideal observing conditions, some hint of nebulosity around

4144-640: The cluster, although they contribute less than 2% of the total mass. Astronomers have made great efforts to find and analyze brown dwarfs in the Pleiades and other young clusters, because they are still relatively bright and observable, while brown dwarfs in older clusters have faded and are much more difficult to study. The brightest stars of the cluster are named the Seven Sisters in early Greek mythology : Sterope , Merope , Electra , Maia , Taygeta , Celaeno , and Alcyone . Later, they were assigned parents, Pleione and Atlas . As daughters of Atlas,

4218-483: The combination of two remarkable elements. The first, which is still valid, is its unique and easily identifiable appearance on the celestial vault near the ecliptic . The second, essential for the ancients, is that in the middle of the third millennium BC, this asterism (a prominent pattern or group of stars that is smaller than a constellation) marked the vernal point . (2330 BC with ecliptic latitude about +3.5° according to Stellarium ) The importance of this asterism

4292-471: The distances to remote galaxies and the expansion rate of the Universe ( Hubble constant ). Indeed, the open cluster NGC 7790 hosts three classical Cepheids which are critical for such efforts. Embedded clusters are groups of very young stars that are partially or fully encased in interstellar dust or gas which is often impervious to optical observations. Embedded clusters form in molecular clouds , when

4366-404: The emission of electromagnetic energy , neutrinos and by the ejection of matter with the solar wind . It is expelling about (2–3) × 10   M ☉ /year. The mass loss rate will increase when the Sun enters the red giant stage, climbing to (7–9) × 10   M ☉ /year when it reaches the tip of the red-giant branch . This will rise to 10   M ☉ /year on

4440-429: The geometry of Earth. The first known estimate of the solar mass was by Isaac Newton . In his work Principia (1687), he estimated that the ratio of the mass of Earth to the Sun was about 1 ⁄ 28 700 . Later he determined that his value was based upon a faulty value for the solar parallax, which he had used to estimate the distance to the Sun. He corrected his estimated ratio to 1 ⁄ 169 282 in

4514-523: The gravity of giant molecular clouds and other clusters. Close encounters between cluster members can also result in the ejection of stars, a process known as "evaporation". The most prominent open clusters are the Pleiades and Hyades in Taurus . The Double Cluster of h + Chi Persei can also be prominent under dark skies. Open clusters are often dominated by hot young blue stars, because although such stars are short-lived in stellar terms, only lasting

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4588-613: The highest-mass brown dwarfs will burn it eventually, and so determining the highest mass of brown dwarfs still containing lithium in the cluster may give an idea of its age. Applying this technique to the Pleiades gives an age of about 115 million years. The cluster is slowly moving in the direction of the feet of what is currently the constellation of Orion . Like most open clusters, the Pleiades will not stay gravitationally bound forever. Some component stars will be ejected after close encounters with other stars; others will be stripped by tidal gravitational fields. Calculations suggest that

4662-544: The inner pair of stars within Atlas (a bright triple star in the Pleiades) favors a distance of 133 to 137 pc. However, the author of the 2007–2009 catalog of revised Hipparcos parallaxes reasserted that the distance to the Pleiades is ~120 pc and challenged the dissenting evidence. In 2012, Francis and Anderson proposed that a systematic effect on Hipparcos parallax errors for stars in clusters would bias calculation using

4736-437: The last 100 million years. Reflection nebulae around the brightest stars were once thought to be leftover material from their formation, but are now considered likely to be an unrelated dust cloud in the interstellar medium through which the stars are currently passing. This dust cloud is estimated to be moving at a speed of approximately 18 km/s relative to the stars in the cluster. Computer simulations have shown that

4810-408: The mass of the Sun is given by solving Kepler's third law : M ⊙ = 4 π 2 × ( 1 A U ) 3 G × ( 1 y r ) 2 {\displaystyle M_{\odot }={\frac {4\pi ^{2}\times (1\,\mathrm {AU} )^{3}}{G\times (1\,\mathrm {yr} )^{2}}}} The value of G

4884-500: The most direct and accurate results. Later work consistently argued that the Hipparcos distance measurement for the Pleiades was erroneous: In particular, distances derived to the cluster via the Hubble Space Telescope and infrared color–magnitude diagram fitting (so-called " spectroscopic parallax ") favor a distance between 135 and 140 pc; a dynamical distance from optical interferometric observations of

4958-739: The name Mutsuraboshi ("six stars") in the eighth-century Kojiki . The cluster is now known in Japan as Subaru. The name was chosen for that of the Subaru Telescope , the 8.2-meter (320 in) flagship telescope of the National Astronomical Observatory of Japan , located at the Mauna Kea Observatory on the island of Hawaii . It had the largest monolithic primary mirror in the world from its commissioning in 1998 until 2005. It also

5032-416: The northwest of the constellation Taurus . At a distance of about 444 light-years , it is among the nearest star clusters to Earth and the nearest Messier object to Earth, being the most obvious star cluster to the naked eye in the night sky . It is also observed to house the reflection nebula NGC 1432 , an HII region . The cluster is dominated by hot blue luminous stars that have formed within

5106-436: The number that would be added if all binary stars could be resolved. Its light is dominated by young, hot blue stars , up to 14 of which may be seen with the naked eye, depending on local observing conditions and visual acuity of the observer. The brightest stars form a shape somewhat similar to that of Ursa Major and Ursa Minor . The total mass contained in the cluster is estimated to be approximately 800 solar masses and

5180-483: The oldest stars of a few hundred million years less. Our Galaxy has about 150 globular clusters, some of which may have been captured cores of small galaxies stripped of stars previously in their outer margins by the tides of the Milky Way , as seems to be the case for the globular cluster M79 . Some galaxies are much richer in globulars than the Milky Way: The giant elliptical galaxy M87 contains over

5254-422: The orbital radius and orbital period of the planet or stars using Kepler's third law. The mass of the Sun cannot be measured directly, and is instead calculated from other measurable factors, using the equation for the orbital period of a small body orbiting a central mass. Based on the length of the year, the distance from Earth to the Sun (an astronomical unit or AU), and the gravitational constant ( G ),

5328-622: The third edition of the Principia . The current value for the solar parallax is smaller still, yielding an estimated mass ratio of 1 ⁄ 332 946 . As a unit of measurement, the solar mass came into use before the AU and the gravitational constant were precisely measured. This is because the relative mass of another planet in the Solar System or the combined mass of two binary stars can be calculated in units of Solar mass directly from

5402-670: The world, including the Celts ( Welsh : Tŵr Tewdws , Irish : Streoillín ); pre-colonial Filipinos (who called it Mapúlon , Mulo‑pulo or Muró‑púro , among other names), for whom it indicated the beginning of the year; Hawaiians (who call them Makaliʻi ), Māori (who call them Matariki ); Indigenous Australians (from several traditions ); the Achaemenid Empire , whence in Persians (who called them Parvīn – پروین – or Parvī – پروی );

5476-410: Was chosen as the brand name of Subaru automobiles to reflect the origins of the firm as the joining of five companies, and is depicted in the firm's six-star logo. Galileo Galilei was the first astronomer to view the Pleiades through a telescope . He thereby discovered that the cluster contains many stars too dim to be seen with the naked eye. He published his observations, including a sketch of

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