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94-563: A number of features exist that are of interest to astronomers. Taurus hosts two of the nearest open clusters to Earth, the Pleiades and the Hyades , both of which are visible to the naked eye. At first magnitude, the red giant Aldebaran is the brightest star in the constellation. In the northeast part of Taurus is Messier 1 , more commonly known as the Crab Nebula, a supernova remnant containing

188-401: A main sequence star. The surrounding reflection nebula NGC 1555 is illuminated by T Tauri, and thus is also variable in luminosity. To the north lies Kappa Tauri , a visual double star consisting of two A7-type components. The pair have a separation of just 5.6 arc minutes, making them a challenge to split with the naked eye. In the northern part of the constellation to the northeast of

282-406: A planetary nebula and evolve into white dwarfs . While most clusters become dispersed before a large proportion of their members have reached the white dwarf stage, the number of white dwarfs in open clusters is still generally much lower than would be expected, given the age of the cluster and the expected initial mass distribution of the stars. One possible explanation for the lack of white dwarfs

376-552: A planisphere . In these ancient cultures, the orientation of the horns was portrayed as upward or backward. This differed from the later Greek depiction where the horns pointed forward. To the Egyptians, the constellation Taurus was a sacred bull that was associated with the renewal of life in spring. When the spring equinox entered Taurus, the constellation would become covered by the Sun in the western sky as spring began. This "sacrifice" led to

470-478: A pulsar . One of the closest regions of active star formation, the Taurus-Auriga complex, crosses into the northern part of the constellation. The variable star T Tauri is the prototype of a class of pre-main-sequence stars . Taurus is a large and prominent constellation in the northern hemisphere 's winter sky, between Aries to the west and Gemini to the east; to the north lies Perseus and Auriga , to

564-485: A common proper motion through space. By comparing the photographic plates of the Pleiades cluster taken in 1918 with images taken in 1943, van Maanen was able to identify those stars that had a proper motion similar to the mean motion of the cluster, and were therefore more likely to be members. Spectroscopic measurements revealed common radial velocities , thus showing that the clusters consist of stars bound together as

658-460: A few billion years. In contrast, the more massive globular clusters of stars exert a stronger gravitational attraction on their members, and can survive for longer. Open clusters have been found only in spiral and irregular galaxies , in which active star formation is occurring. Young open clusters may be contained within the molecular cloud from which they formed, illuminating it to create an H II region . Over time, radiation pressure from

752-461: A great deal of intrinsic difference between a very sparse globular cluster such as Palomar 12 and a very rich open cluster. Some astronomers believe the two types of star clusters form via the same basic mechanism, with the difference being that the conditions that allowed the formation of the very rich globular clusters containing hundreds of thousands of stars no longer prevail in the Milky Way. It

846-440: A group. The first color–magnitude diagrams of open clusters were published by Ejnar Hertzsprung in 1911, giving the plot for the Pleiades and Hyades star clusters . He continued this work on open clusters for the next twenty years. From spectroscopic data, he was able to determine the upper limit of internal motions for open clusters, and could estimate that the total mass of these objects did not exceed several hundred times

940-418: A mean apparent magnitude of +3.40. It is classified as a Delta Scuti type variable star and its brightness varies from magnitude +3.35 to +3.42 with a period of 1.82 hours. Its primary component, Theta Tauri Aa, is a white A-type giant . The secondary, Theta Tauri Ab, is of the 6th magnitude and is 0.005 arcseconds , or at least 2 AU, distant. It completes an orbit once every 141 days. Theta Tauri B

1034-449: A molecular cloud. The gravitational tidal forces generated by such an encounter tend to disrupt the cluster. Eventually, the cluster becomes a stream of stars, not close enough to be a cluster but all related and moving in similar directions at similar speeds. The timescale over which a cluster disrupts depends on its initial stellar density, with more tightly packed clusters persisting longer. Estimated cluster half lives , after which half

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1128-458: A more irregular shape. These were generally found in or near the galactic plane of the Milky Way. Astronomers dubbed the former globular clusters , and the latter open clusters. Because of their location, open clusters are occasionally referred to as galactic clusters , a term that was introduced in 1925 by the Swiss-American astronomer Robert Julius Trumpler . Micrometer measurements of

1222-406: A particularly dense form known as infrared dark clouds , eventually leading to the formation of up to several thousand stars. This star formation begins enshrouded in the collapsing cloud, blocking the protostars from sight but allowing infrared observation. In the Milky Way galaxy, the formation rate of open clusters is estimated to be one every few thousand years. The hottest and most massive of

1316-531: A polygon of 26 segments. In the equatorial coordinate system , the right ascension coordinates of these borders lie between 03 23.4 and 05 53.3 , while the declination coordinates are between 31.10° and −1.35°. Because a small part of the constellation lies to the south of the celestial equator , this can not be a completely circumpolar constellation at any latitude. There are four stars above magnitude 3 in Taurus. The brightest member of this constellation

1410-475: A rate of 1° east every 72 years until approximately 2600 AD, at which point it will be in Aries on the first day of summer. As of 2008, the Sun appears in the constellation Taurus from May 13 to June 21. In tropical astrology , the Sun is considered to be in the sign Taurus from April 20 to May 20. The space probe Pioneer 10 is moving in the direction of this constellation, though it will not be nearing any of

1504-475: A single star, but groupings of many stars. For Praesepe, he found more than 40 stars. Where previously observers had noted only 6–7 stars in the Pleiades, he found almost 50. In his 1610 treatise Sidereus Nuncius , Galileo Galilei wrote, "the galaxy is nothing else but a mass of innumerable stars planted together in clusters." Influenced by Galileo's work, the Sicilian astronomer Giovanni Hodierna became possibly

1598-410: A star will have an encounter with another member every 10 million years. The rate is even higher in denser clusters. These encounters can have a significant impact on the extended circumstellar disks of material that surround many young stars. Tidal perturbations of large disks may result in the formation of massive planets and brown dwarfs , producing companions at distances of 100  AU or more from

1692-481: A third of the original stars, with the remainder becoming unbound once the gas is expelled. The young stars so released from their natal cluster become part of the Galactic field population. Because most if not all stars form in clusters, star clusters are to be viewed as the fundamental building blocks of galaxies. The violent gas-expulsion events that shape and destroy many star clusters at birth leave their imprint in

1786-428: A variation of their net magnitude throughout each orbit. Located about 1.8° west of Epsilon (ε) Tauri is T Tauri , the prototype of a class of variable stars called T Tauri stars . This star undergoes erratic changes in luminosity, varying between magnitude 9 to 13 over a period of weeks or months. This is a newly formed stellar object that is just emerging from its envelope of gas and dust, but has not yet become

1880-516: A younger age than their counterparts in the outer regions. Because open clusters tend to be dispersed before most of their stars reach the end of their lives, the light from them tends to be dominated by the young, hot blue stars. These stars are the most massive, and have the shortest lives, a few tens of millions of years. The older open clusters tend to contain more yellow stars. The frequency of binary star systems has been observed to be higher within open clusters than outside open clusters. This

1974-653: Is Berkeley 29 , at a distance of about 15,000 parsecs. Open clusters, especially super star clusters , are also easily detected in many of the galaxies of the Local Group and nearby: e.g., NGC 346 and the SSCs R136 and NGC 1569 A and B . Accurate knowledge of open cluster distances is vital for calibrating the period–luminosity relationship shown by variable stars such as Cepheid stars, which allows them to be used as standard candles . These luminous stars can be detected at great distances, and are then used to extend

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2068-409: Is Aldebaran, an orange-hued, spectral class K5 III giant star . Its name derives from الدبران al-dabarān , Arabic for "the follower", probably from the fact that it follows the Pleiades during the nightly motion of the celestial sphere across the sky. Forming the profile of a Bull's face is a V or K -shaped asterism of stars. This outline is created by prominent members of

2162-544: Is a white, spectral class B7 III giant star known as El Nath , which comes from the Arabic phrase "the butting", as in butting by the horns of the bull. At magnitude 1.65, it is the second brightest star in the constellation, and shares the border with the neighboring constellation of Auriga. As a result, it also bears the designation Gamma Aurigae. Zeta Tauri (the proper name is Tianguan ) is an eclipsing binary star that completes an orbit every 133 days. The star Lambda (λ) Tauri

2256-535: Is an eclipsing binary star. This system consists of a spectral class B3 star being orbited by a less massive class A4 star. The plane of their orbit lies almost along the line of sight to the Earth. Every 3.953 days the system temporarily decreases in brightness by 1.1 magnitudes as the brighter star is partially eclipsed by the dimmer companion. The two stars are separated by only 0.1 astronomical units , so their shapes are modified by mutual tidal interaction. This results in

2350-563: Is common for two or more separate open clusters to form out of the same molecular cloud. In the Large Magellanic Cloud , both Hodge 301 and R136 have formed from the gases of the Tarantula Nebula , while in our own galaxy, tracing back the motion through space of the Hyades and Praesepe , two prominent nearby open clusters, suggests that they formed in the same cloud about 600 million years ago. Sometimes, two clusters born at

2444-511: Is depicted; this was sometimes explained as Taurus being partly submerged as he carried Europa out to sea. A second Greek myth portrays Taurus as Io , a mistress of Zeus. To hide his lover from his wife Hera , Zeus changed Io into the form of a heifer. Greek mythographer Acusilaus marks the bull Taurus as the same that formed the myth of the Cretan Bull , one of The Twelve Labors of Heracles . Taurus became an important object of worship among

2538-409: Is estimated to dissipate in another 250 million years. The Pleiades cluster is classified as a Shapley class c and Trumpler class I 3 r n cluster, indicating that it is irregularly shaped and loose, though concentrated at its center and detached from the star-field. To the east, the two horns of the bull are formed by Beta (β) Tauri and Zeta (ζ) Tauri ; two star systems that are separated by 8°. Beta

2632-464: Is loosely bound by mutual gravitational attraction and becomes disrupted by close encounters with other clusters and clouds of gas as they orbit the Galactic Center . This can result in a loss of cluster members through internal close encounters and a dispersion into the main body of the galaxy. Open clusters generally survive for a few hundred million years, with the most massive ones surviving for

2726-581: Is now so included in the List of IAU-approved Star Names. In Chinese , 畢宿 ( Bì Xiù ), meaning Net , refers to an asterism consisting of Theta² Tauri, Epsilon Tauri (named Ain), Delta³ Tauri , Delta¹ Tauri , Gamma Tauri , Alpha Tauri ( Aldebaran ), 71 Tauri and Lambda Tauri . Consequently, the Chinese name for Theta² Tauri itself is 畢宿六 ( Bì Xiù liù ), "the Sixth Star of Net". Theta Tauri A has

2820-407: Is seen as evidence that single stars get ejected from open clusters due to dynamical interactions. Some open clusters contain hot blue stars which seem to be much younger than the rest of the cluster. These blue stragglers are also observed in globular clusters, and in the very dense cores of globulars they are believed to arise when stars collide, forming a much hotter, more massive star. However,

2914-411: Is that when a red giant expels its outer layers to become a planetary nebula, a slight asymmetry in the loss of material could give the star a 'kick' of a few kilometres per second , enough to eject it from the cluster. Because of their high density, close encounters between stars in an open cluster are common. For a typical cluster with 1,000 stars with a 0.5 parsec half-mass radius, on average

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3008-560: Is the double star's Bayer designation ; θ Tauri and θ Tauri those of its two constituents. The designations of the two constituents as Theta Tauri A and B , and those of the four components - Theta Tauri Aa , Ab , Ba and Bb - derive from the convention used by the Washington Multiplicity Catalog (WMC) for multiple star systems , and adopted by the International Astronomical Union (IAU). In

3102-442: Is the only constellation crossed by all three of the galactic equator, celestial equator, and ecliptic. A ring-like galactic structure known as Gould's Belt passes through the constellation. The recommended three-letter abbreviation for the constellation, as adopted by the International Astronomical Union in 1922, is "Tau". The official constellation boundaries, as set by Belgian astronomer Eugène Delporte in 1930, are defined by

3196-404: Is the so-called moving cluster method . This relies on the fact that the stars of a cluster share a common motion through space. Measuring the proper motions of cluster members and plotting their apparent motions across the sky will reveal that they converge on a vanishing point . The radial velocity of cluster members can be determined from Doppler shift measurements of their spectra , and once

3290-553: The Beehive Cluster . Theta Tauri Theta Tauri ( θ Tauri , abbreviated Theta Tau , θ Tau ) is a wide double star in the constellation of Taurus and a member of the Hyades open cluster . θ Tauri is composed of two 3rd magnitude stars, designated Theta Tauri ( Theta Tauri B ) and Theta Tauri ( Theta Tauri A ). Theta² is brighter, hence the pair are sometimes referred to as Theta Tauri B and A, respectively. They are separated by 5.62 arcminutes (0.094°) on

3384-641: The Chalcolithic and the Early Bronze Age , from about 4000 BC to 1700 BC, after which it moved into the neighboring constellation Aries. The Pleiades were closest to the Sun at vernal equinox around the 23rd century BC . In Babylonian astronomy , the constellation was listed in the MUL.APIN as GU 4 .AN.NA , "The Bull of Heaven ". Although it has been claimed that "when the Babylonians first set up their zodiac,

3478-594: The Druids . Their Tauric religious festival was held while the Sun passed through the constellation. Among the arctic people known as the Inuit , the constellation is called Sakiattiat and the Hyades is Nanurjuk, with the latter representing the spirit of the polar bear . Aldebaran represents the bear, with the remainder of the stars in the Hyades being dogs that are holding the beast at bay. In Buddhism , legends hold that Gautama Buddha

3572-408: The Galactic Center , generally at substantial distances above or below the galactic plane . Tidal forces are stronger nearer the center of the galaxy, increasing the rate of disruption of clusters, and also the giant molecular clouds which cause the disruption of clusters are concentrated towards the inner regions of the galaxy, so clusters in the inner regions of the galaxy tend to get dispersed at

3666-526: The Hyades , the nearest distinct open star cluster after the Ursa Major Moving Group . In this profile, Aldebaran forms the bull's bloodshot eye, which has been described as "glaring menacingly at the hunter Orion", a constellation that lies just to the southeast. Aldebaran has around 116% the mass of the Sun. It also hosts a candidate exoplanet. The Hyades span about 5° of the sky, so that they can only be viewed in their entirety with binoculars or

3760-544: The Pleiades , the Hyades and the Alpha Persei Cluster , are visible with the naked eye. Some others, such as the Double Cluster , are barely perceptible without instruments, while many more can be seen using binoculars or telescopes . The Wild Duck Cluster , M11, is an example. The prominent open cluster the Pleiades , in the constellation Taurus, has been recognized as a group of stars since antiquity, while

3854-577: The Southern Taurids are active; though the latter stream is stronger. However, between November 1 and 10, the two streams equalize. The identification of the constellation of Taurus with a bull is very old, certainly dating to the Chalcolithic , and perhaps even to the Upper Paleolithic . Michael Rappenglück of the University of Munich believes that Taurus is represented in a cave painting at

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3948-510: The Sun according to his general theory of relativity which he published in 1915. Open cluster An open cluster is a type of star cluster made of tens to a few thousand stars that were formed from the same giant molecular cloud and have roughly the same age. More than 1,100 open clusters have been discovered within the Milky Way galaxy, and many more are thought to exist. Each one

4042-427: The Ursa Major Moving Group . Eventually their slightly different relative velocities will see them scattered throughout the galaxy. A larger cluster is then known as a stream, if we discover the similar velocities and ages of otherwise well-separated stars. When a Hertzsprung–Russell diagram is plotted for an open cluster, most stars lie on the main sequence . The most massive stars have begun to evolve away from

4136-486: The celestial sphere forms the apparent path of the Sun as the Earth completes its annual orbit. As the orbital plane of the Moon and the planets lie near the ecliptic, they can usually be found in the constellation Taurus during some part of each year. The galactic plane of the Milky Way intersects the northeast corner of the constellation and the galactic anticenter is located near the border between Taurus and Auriga. Taurus

4230-663: The main sequence on the Hertzsprung–Russell diagram for a cluster at a known distance with that of a more distant cluster, the distance to the more distant cluster can be estimated. The nearest open cluster is the Hyades: The stellar association consisting of most of the Plough stars is at about half the distance of the Hyades, but is a stellar association rather than an open cluster as the stars are not gravitationally bound to each other. The most distant known open cluster in our galaxy

4324-425: The mass of the Sun . These clouds have densities that vary from 10 to 10 molecules of neutral hydrogen per cm , with star formation occurring in regions with densities above 10 molecules per cm . Typically, only 1–10% of the cloud by volume is above the latter density. Prior to collapse, these clouds maintain their mechanical equilibrium through magnetic fields, turbulence and rotation. Many factors may disrupt

4418-587: The mythology of the Maya peoples , Theta Tauri is known as Chamukuy , meaning a small bird in the Yucatec Maya language . In 2016, the IAU organized a Working Group on Star Names (WGSN) to catalog and standardize proper names for stars. The WGSN decided to attribute proper names to individual stars rather than entire multiple systems . It approved the name Chamukuy for the component Theta Tauri Aa on 5 September 2017 and it

4512-566: The parallax (the small change in apparent position over the course of a year caused by the Earth moving from one side of its orbit around the Sun to the other) of stars in close open clusters can be measured, like other individual stars. Clusters such as the Pleiades, Hyades and a few others within about 500 light years are close enough for this method to be viable, and results from the Hipparcos position-measuring satellite yielded accurate distances for several clusters. The other direct method

4606-481: The Danish–Irish astronomer J. L. E. Dreyer , and the two supplemental Index Catalogues , published in 1896 and 1905. Telescopic observations revealed two distinct types of clusters, one of which contained thousands of stars in a regular spherical distribution and was found all across the sky but preferentially towards the center of the Milky Way . The other type consisted of a generally sparser population of stars in

4700-523: The Hall of the Bulls in the caves at Lascaux (dated to roughly 15,000 BC), which he believes is accompanied by a depiction of the Pleiades. The name "seven sisters" has been used for the Pleiades in the languages of many cultures, including indigenous groups of Australia , North America and Siberia . This suggests that the name may have a common ancient origin. Taurus marked the point of vernal (spring) equinox in

4794-818: The Hyades (which also form part of Taurus ) is one of the oldest open clusters. Other open clusters were noted by early astronomers as unresolved fuzzy patches of light. In his Almagest , the Roman astronomer Ptolemy mentions the Praesepe cluster, the Double Cluster in Perseus , the Coma Star Cluster and the Ptolemy Cluster , while the Persian astronomer Al-Sufi wrote of the Omicron Velorum cluster . However, it would require

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4888-403: The Milky Way to appear close to each other. Open clusters range from very sparse clusters with only a few members to large agglomerations containing thousands of stars. They usually consist of quite a distinct dense core, surrounded by a more diffuse 'corona' of cluster members. The core is typically about 3–4  light years across, with the corona extending to about 20 light years from

4982-514: The Pleiades being the result of a chance alignment as seen from Earth was just 1 in 496,000. Between 1774 and 1781, French astronomer Charles Messier published a catalogue of celestial objects that had a nebulous appearance similar to comets . This catalogue included 26 open clusters. In the 1790s, English astronomer William Herschel began an extensive study of nebulous celestial objects. He discovered that many of these features could be resolved into groupings of individual stars. Herschel conceived

5076-469: The Pleiades lies the Crystal Ball Nebula, known by its catalogue designation of NGC 1514 . This planetary nebula is of historical interest following its discovery by German-born English astronomer William Herschel in 1790. Prior to that time, astronomers had assumed that nebulae were simply unresolved groups of stars. However, Herschel could clearly resolve a star at the center of the nebula that

5170-494: The Taurus-Auriga complex, or Taurus dark clouds, a star-forming region containing sparse, filamentary clouds of gas and dust. This spans a diameter of 98 light-years (30 parsecs ) and contains 35,000  solar masses of material, which is both larger and less massive than the Orion Nebula . At a distance of 490 light-years (150 parsecs), this is one of the nearest active star forming regions. Located in this region, about 10° to

5264-412: The abundances of these light elements are much lower than models of stellar evolution predict. While the reason for this underabundance is not yet fully understood, one possibility is that convection in stellar interiors can 'overshoot' into regions where radiation is normally the dominant mode of energy transport. Determining the distances to astronomical objects is crucial to understanding them, but

5358-450: The cluster center. Typical star densities in the center of a cluster are about 1.5 stars per cubic light year ; the stellar density near the Sun is about 0.003 stars per cubic light year. Open clusters are often classified according to a scheme developed by Robert Trumpler in 1930. The Trumpler scheme gives a cluster a three-part designation, with a Roman numeral from I-IV for little to very disparate, an Arabic numeral from 1 to 3 for

5452-407: The cluster is also named the "Seven Sisters". However, many more stars are visible with even a modest telescope. Astronomers estimate that the cluster has approximately 500–1,000 stars, all of which are around 100 million years old. However, they vary considerably in type. The Pleiades themselves are represented by large, bright stars; also many small brown dwarfs and white dwarfs exist. The cluster

5546-503: The cluster will disperse the molecular cloud. Typically, about 10% of the mass of a gas cloud will coalesce into stars before radiation pressure drives the rest of the gas away. Open clusters are key objects in the study of stellar evolution . Because the cluster members are of similar age and chemical composition , their properties (such as distance, age, metallicity , extinction , and velocity) are more easily determined than they are for isolated stars. A number of open clusters, such as

5640-516: The day and is mentioned in Chinese historical texts. At its peak, the supernova reached magnitude −4, but the nebula is currently magnitude 8.4 and requires a telescope to observe. North American peoples also observed the supernova, as evidenced from a painting on a New Mexican canyon and various pieces of pottery that depict the event. However, the remnant itself was not discovered until 1731, when John Bevis found it. This constellation includes part of

5734-566: The distance scale to nearby galaxies in the Local Group. Indeed, the open cluster designated NGC 7790 hosts three classical Cepheids . RR Lyrae variables are too old to be associated with open clusters, and are instead found in globular clusters . The stars in open clusters can host exoplanets, just like stars outside open clusters. For example, the open cluster NGC 6811 contains two known planetary systems, Kepler-66 and Kepler-67 . Additionally, several hot Jupiters are known to exist in

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5828-482: The equilibrium of a giant molecular cloud, triggering a collapse and initiating the burst of star formation that can result in an open cluster. These include shock waves from a nearby supernova , collisions with other clouds and gravitational interactions. Even without external triggers, regions of the cloud can reach conditions where they become unstable against collapse. The collapsing cloud region will undergo hierarchical fragmentation into ever smaller clumps, including

5922-521: The first astronomer to use a telescope to find previously undiscovered open clusters. In 1654, he identified the objects now designated Messier 41 , Messier 47 , NGC 2362 and NGC 2451 . It was realized as early as 1767 that the stars in a cluster were physically related, when the English naturalist the Reverend John Michell calculated that the probability of even just one group of stars like

6016-491: The galaxy, although their concentration is highest where the gas density is highest. Open clusters are not seen in elliptical galaxies : Star formation ceased many millions of years ago in ellipticals, and so the open clusters which were originally present have long since dispersed. In the Milky Way Galaxy, the distribution of clusters depends on age, with older clusters being preferentially found at greater distances from

6110-504: The host star. Many open clusters are inherently unstable, with a small enough mass that the escape velocity of the system is lower than the average velocity of the constituent stars. These clusters will rapidly disperse within a few million years. In many cases, the stripping away of the gas from which the cluster formed by the radiation pressure of the hot young stars reduces the cluster mass enough to allow rapid dispersal. Clusters that have enough mass to be gravitationally bound once

6204-511: The idea that stars were initially scattered across space, but later became clustered together as star systems because of gravitational attraction. He divided the nebulae into eight classes, with classes VI through VIII being used to classify clusters of stars. The number of clusters known continued to increase under the efforts of astronomers. Hundreds of open clusters were listed in the New General Catalogue , first published in 1888 by

6298-499: The invention of the telescope to resolve these "nebulae" into their constituent stars. Indeed, in 1603 Johann Bayer gave three of these clusters designations as if they were single stars. The first person to use a telescope to observe the night sky and record his observations was the Italian scientist Galileo Galilei in 1609. When he turned the telescope toward some of the nebulous patches recorded by Ptolemy, he found they were not

6392-436: The main sequence and are becoming red giants ; the position of the turn-off from the main sequence can be used to estimate the age of the cluster. Because the stars in an open cluster are all at roughly the same distance from Earth , and were born at roughly the same time from the same raw material, the differences in apparent brightness among cluster members are due only to their mass. This makes open clusters very useful in

6486-471: The mass of the Sun. He demonstrated a relationship between the star colors and their magnitudes, and in 1929 noticed that the Hyades and Praesepe clusters had different stellar populations than the Pleiades. This would subsequently be interpreted as a difference in ages of the three clusters. The formation of an open cluster begins with the collapse of part of a giant molecular cloud , a cold dense cloud of gas and dust containing up to many thousands of times

6580-431: The morphological and kinematical structures of galaxies. Most open clusters form with at least 100 stars and a mass of 50 or more solar masses. The largest clusters can have over 10 solar masses, with the massive cluster Westerlund 1 being estimated at 5 × 10 solar masses and R136 at almost 5 x 10 , typical of globular clusters. While open clusters and globular clusters form two fairly distinct groups, there may not be

6674-468: The newly formed stars (known as OB stars ) will emit intense ultraviolet radiation , which steadily ionizes the surrounding gas of the giant molecular cloud, forming an H II region . Stellar winds and radiation pressure from the massive stars begins to drive away the hot ionized gas at a velocity matching the speed of sound in the gas. After a few million years the cluster will experience its first core-collapse supernovae , which will also expel gas from

6768-511: The northeast of Aldebaran, is an asterism NGC 1746 spanning a width of 45 arcminutes . During November, the Taurid meteor shower appears to radiate from the general direction of this constellation. The Beta Taurid meteor shower occurs during the months of June and July in the daytime, and is normally observed using radio techniques. Between 18 and 29 October, both the Northern Taurids and

6862-534: The oldest depictions shows the bull standing before the goddess' standard; since it has 3 stars depicted on its back (the cuneiform sign for "star-constellation"), there is good reason to regard this as the constellation later known as Taurus. The same iconic representation of the Heavenly Bull was depicted in the Dendera zodiac , an Egyptian bas-relief carving in a ceiling that depicted the celestial hemisphere using

6956-495: The original cluster members will have been lost, range from 150–800 million years, depending on the original density. After a cluster has become gravitationally unbound, many of its constituent stars will still be moving through space on similar trajectories, in what is known as a stellar association , moving cluster, or moving group . Several of the brightest stars in the ' Plough ' of Ursa Major are former members of an open cluster which now form such an association, in this case

7050-692: The positions of stars in clusters were made as early as 1877 by the German astronomer E. Schönfeld and further pursued by the American astronomer E. E. Barnard prior to his death in 1923. No indication of stellar motion was detected by these efforts. However, in 1918 the Dutch–American astronomer Adriaan van Maanen was able to measure the proper motion of stars in part of the Pleiades cluster by comparing photographic plates taken at different times. As astrometry became more accurate, cluster stars were found to share

7144-436: The radial velocity, proper motion and angular distance from the cluster to its vanishing point are known, simple trigonometry will reveal the distance to the cluster. The Hyades are the best-known application of this method, which reveals their distance to be 46.3  parsecs . Once the distances to nearby clusters have been established, further techniques can extend the distance scale to more distant clusters. By matching

7238-551: The range in brightness of members (from small to large range), and p , m or r to indication whether the cluster is poor, medium or rich in stars. An 'n' is appended if the cluster lies within nebulosity . Under the Trumpler scheme, the Pleiades are classified as I3rn, and the nearby Hyades are classified as II3m. There are over 1,100 known open clusters in our galaxy, but the true total may be up to ten times higher than that. In spiral galaxies , open clusters are largely found in

7332-426: The renewal of the land. To the early Hebrews , Taurus was the first constellation in their zodiac and consequently it was represented by the first letter in their alphabet, Aleph . In Greek mythology , Taurus was identified with Zeus , who assumed the form of a magnificent white bull to abduct Europa , a legendary Phoenician princess. In illustrations of Greek mythology, only the front portion of this constellation

7426-660: The same time will form a binary cluster. The best known example in the Milky Way is the Double Cluster of NGC 869 and NGC 884 (also known as h and χ Persei), but at least 10 more double clusters are known to exist. New research indicates the Cepheid -hosting M25 may constitute a ternary star cluster together with NGC 6716 and Collinder 394. Many more binary clusters are known in the Small and Large Magellanic Clouds—they are easier to detect in external systems than in our own galaxy because projection effects can cause unrelated clusters within

7520-517: The sky where they become the stars we know as Ursa Major and Ursa Minor. Some locate Gilgamesh as the neighboring constellation of Orion, facing Taurus as if in combat, while others identify him with the sun whose rising on the equinox vanquishes the constellation. In early Mesopotamian art, the Bull of Heaven was closely associated with Inanna , the Sumerian goddess of sexual love, fertility, and warfare. One of

7614-407: The sky. Based upon parallax measurements, Theta¹ Tauri is located at a distance of 152 ly (47 pc), while Theta² Tauri is at a distance of 157 light-years (48 parsecs). θ Tauri A and B are both spectroscopic binaries ; the four components are designated Theta Tauri Aa (formally named Chamukuy / ˈ tʃ ɑː m uː k uː i / ), Ab, Ba, and Bb. θ Tauri ( Latinised to Theta Tauri )

7708-460: The southeast Orion , to the south Eridanus , and to the southwest Cetus . In late November-early December, Taurus reaches opposition (furthest point from the Sun) and is visible the entire night. By late March, it is setting at sunset and completely disappears behind the Sun's glare from May to July. This constellation forms part of the zodiac and hence is intersected by the ecliptic . This circle across

7802-449: The spiral arms where gas densities are highest and so most star formation occurs, and clusters usually disperse before they have had time to travel beyond their spiral arm. Open clusters are strongly concentrated close to the galactic plane, with a scale height in our galaxy of about 180 light years, compared with a galactic radius of approximately 50,000 light years. In irregular galaxies , open clusters may be found throughout

7896-399: The star formation process. All clusters thus suffer significant infant weight loss, while a large fraction undergo infant mortality. At this point, the formation of an open cluster will depend on whether the newly formed stars are gravitationally bound to each other; otherwise an unbound stellar association will result. Even when a cluster such as the Pleiades does form, it may hold on to only

7990-509: The stars in this constellation for many thousands of years, by which time its batteries will be long dead. Several stars in the Hyades star cluster, including Kappa Tauri , were photographed during the total solar eclipse of May 29, 1919 , by the expedition of Arthur Eddington in Príncipe and others in Sobral, Brazil , that confirmed Albert Einstein 's prediction of the bending of light around

8084-454: The stellar density in open clusters is much lower than that in globular clusters, and stellar collisions cannot explain the numbers of blue stragglers observed. Instead, it is thought that most of them probably originate when dynamical interactions with other stars cause a binary system to coalesce into one star. Once they have exhausted their supply of hydrogen through nuclear fusion , medium- to low-mass stars shed their outer layers to form

8178-750: The study of stellar evolution, because when comparing one star with another, many of the variable parameters are fixed. The study of the abundances of lithium and beryllium in open-cluster stars can give important clues about the evolution of stars and their interior structures. While hydrogen nuclei cannot fuse to form helium until the temperature reaches about 10 million  K , lithium and beryllium are destroyed at temperatures of 2.5 million K and 3.5 million K respectively. This means that their abundances depend strongly on how much mixing occurs in stellar interiors. Through study of their abundances in open-cluster stars, variables such as age and chemical composition can be fixed. Studies have shown that

8272-501: The surrounding nebula has evaporated can remain distinct for many tens of millions of years, but, over time, internal and external processes tend also to disperse them. Internally, close encounters between stars can increase the velocity of a member beyond the escape velocity of the cluster. This results in the gradual 'evaporation' of cluster members. Externally, about every half-billion years or so an open cluster tends to be disturbed by external factors such as passing close to or through

8366-405: The unaided eye. It includes a naked eye double star, Theta Tauri (the proper name of Theta Tauri is Chamukuy ), with a separation of 5.6  arcminutes . In the northwestern quadrant of the Taurus constellation lie the Pleiades ( M45 ), one of the best known open clusters, easily visible to the naked eye. The seven most prominent stars in this cluster are at least visual magnitude six, and so

8460-472: The vast majority of objects are too far away for their distances to be directly determined. Calibration of the astronomical distance scale relies on a sequence of indirect and sometimes uncertain measurements relating the closest objects, for which distances can be directly measured, to increasingly distant objects. Open clusters are a crucial step in this sequence. The closest open clusters can have their distance measured directly by one of two methods. First,

8554-621: The vernal equinox lay in Taurus," there is a claim that the MUL.APIN tablets indicate that the vernal equinox was marked by the Babylonian constellation known as "the hired man" (the modern Aries). In the Old Babylonian Epic of Gilgamesh , the goddess Ishtar sends Taurus, the Bull of Heaven , to kill Gilgamesh for spurning her advances. Enkidu tears off the bull's hind part and hurls the quarters into

8648-418: The vicinity. In most cases these processes will strip the cluster of gas within ten million years, and no further star formation will take place. Still, about half of the resulting protostellar objects will be left surrounded by circumstellar disks , many of which form accretion disks. As only 30 to 40 percent of the gas in the cloud core forms stars, the process of residual gas expulsion is highly damaging to

8742-515: Was born when the full moon was in Vaisakha , or Taurus. Buddha's birthday is celebrated with the Wesak Festival, or Vesākha , which occurs on the first or second full moon when the Sun is in Taurus. In 1990, due to the precession of the equinoxes , the position of the Sun on the first day of summer (June 21) crossed the IAU boundary of Gemini into Taurus. The Sun will slowly move through Taurus at

8836-490: Was surrounded by a nebulous cloud of some type. In 1864, English astronomer William Huggins used the spectrum of this nebula to deduce that the nebula is a luminous gas, rather than stars. North-west of ζ Tauri by 1.15 degrees is the Crab Nebula (M1), a supernova remnant. This expanding nebula was created by a Type II supernova explosion, which was seen from Earth on July 4, 1054. It was bright enough to be observed during

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