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95-468: The Southern Cross or Crux , a constellation visible in the Southern Hemisphere , is depicted on flags and coats of arms of various countries and sub-national entities. This star constellation is visible mostly in the southern hemisphere and it therefore symbolises the southern location of its users. The term Southern Cross can also refer to the blue saltire as used in various flags of

190-406: 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

285-510: 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 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

380-546: A cluster such as the Pleiades does form, it may hold on to only 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

475-534: 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 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

570-461: 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

665-509: A letter to the monarch describing his observations of the southern sky, which included a rather crude map of the stars around the south celestial pole including the Southern Cross and the two Magellanic Clouds seen in an external orientation, as on a globe. Emery Molyneux and Petrus Plancius have also been cited as the first uranographers (sky mappers) to distinguish Crux as a separate constellation; their representations date from 1592,

760-557: A line from γ to α Crucis (the foot of the crucifix) approximately 4 + 1 ⁄ 2 times beyond gives a point close to the Southern Celestial Pole which is also, coincidentally, where intersects a perpendicular line taken southwards from the east–west axis of Alpha Centauri to Beta Centauri , which are stars at an alike declination to Crux and of a similar width as the cross, but higher magnitude. Argentine gauchos are documented as using Crux for night orientation in

855-490: 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 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

950-449: 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

1045-538: A planet— HD 106906 b —that has one of the widest orbits of any currently known planetary-mass companions. Crux is backlit by the multitude of stars of the Scutum-Crux Arm (more commonly called the Scutum-Centaurus Arm ) of the Milky Way. This is the main inner arm in the local radial quarter of the galaxy. Part-obscuring this is: A key feature of the Scutum-Crux Arm is: The most prominent feature of Crux

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1140-410: 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

1235-531: 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 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

1330-661: A term that was introduced in 1925 by the Swiss-American astronomer Robert Julius Trumpler . Micrometer measurements of 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

1425-516: 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

1520-653: 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

1615-764: Is a major rail terminal in Melbourne, Australia. The Personal Ordinariate of Our Lady of the Southern Cross is a personal ordinariate of the Roman Catholic Church primarily within the territory of the Australian Catholic Bishops Conference for groups of Anglicans who desire full communion with the Catholic Church in Australia and Asia. The Knights of the Southern Cross (KSC) is a Catholic fraternal order throughout Australia. In India, there

1710-520: Is a story related to the creation of Trishanku Swarga (त्रिशंकु), meaning Cross (Crux), created by Sage Vishwamitra . In Chinese , 十字架 ( Shí Zì Jià ), meaning Cross , refers to an asterism consisting of γ Crucis, α Crucis , β Crucis and δ Crucis . In Australian Aboriginal astronomy , Crux and the Coalsack mark the head of the 'Emu in the Sky' (which is seen in the dark spaces rather than in

1805-569: Is also mentioned in the Samoan National Anthem . " Vaai 'i na fetu o lo'u a agiagia ai: Le faailoga lea o Iesu, na maliu ai mo Samoa. " ("Look at those stars that are waving on it: This is the symbol of Jesus, who died on it for Samoa.") The 1952-53 NBC Television Series Victory At Sea contained a musical number entitled "Beneath the Southern Cross". " Southern Cross " is a single released by Crosby, Stills and Nash in 1981. It reached #18 on Billboard Hot 100 in late 1982. "The Sign of

1900-592: Is also shared by an archaic name of the constellation in Vietnam , where it was once known as sao Cá Liệt (the ponyfish star). Among Filipino people , the southern cross have various names pertaining to tops , including kasing ( Visayan languages ), paglong ( Bikol ), and pasil ( Tagalog ). It is also called butiti ( puffer fish ) in Waray . The Javanese people of Indonesia called this constellation Gubug pèncèng ("raking hut") or lumbung ("the granary"), because

1995-480: Is also visible near the horizon from tropical latitudes of the northern hemisphere for a few hours every night during the northern winter and spring. For instance, it is visible from Cancun or any other place at latitude 25° N or less at around 10 pm at the end of April. There are 5 main stars. Due to precession , Crux will move closer to the South Pole in the next millennia, up to 67 degrees south declination for

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2090-611: 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

2185-454: 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 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

2280-400: 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 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

2375-407: 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,

2470-411: 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

2565-496: Is the distinctive asterism known as the Southern Cross. It has great significance in the cultures of the southern hemisphere, particularly of Australia, Brazil, Chile and New Zealand. Several southern countries and organisations have traditionally used Crux as a national or distinctive symbol. The four or five brightest stars of Crux appear, heraldically standardised in various ways, on the flags of Australia , Brazil , New Zealand , Papua New Guinea and Samoa . They also appear on

2660-404: 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

2755-543: The Ancient Greeks , where Ptolemy regarded them as part of the constellation Centaurus . They were entirely visible as far north as Britain in the fourth millennium BC. However, the precession of the equinoxes gradually lowered the stars below the European horizon, and they were eventually forgotten by the inhabitants of northern latitudes. By 400  AD , the stars in the constellation now called Crux never rose above

2850-556: The Brazilian coat of arms and, as of July 2015 , on the cover of Brazilian passports . Five stars appear in the logo of the Brazilian football team Cruzeiro Esporte Clube and in the insignia of the Order of the Southern Cross , and the cross has featured as name of the Brazilian currency (the cruzeiro from 1942 to 1986 and again from 1990 to 1994). All coins of the current (1998) series of

2945-519: The Brazilian real display the constellation. Songs and literature reference the Southern Cross, including the Argentine epic poem Martín Fierro . The Argentinian singer Charly García says that he is "from the Southern Cross" in the song "No voy en tren". The Cross gets a mention in the lyrics of the Brazilian National Anthem (1909): " A imagem do Cruzeiro resplandece " ("the image of

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3040-660: 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 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 ,

3135-738: The Federal Senate Flag of Assis Flag of Bom Sucesso do Sul Flag of Cachoeiro de Itapemirim Flag of Cruzeiro do Sul, Acre Flag of Diamantino Flag of Extrema Flag of Goiás Flag of Goioerê Flag of Igaporã Flag of Ijuí Flag of Ilha Comprida Flag of Itamarandiba Flag of Itauçu Flag of Jaguaripe Flag of Joinville Flag of Londrina Flag of Mairiporã Flag of Maringá Flag of Monte Santo, Bahia Flag of Paraná Flag of Cruzeiro do Sul, Paraná Flag of Peruíbe Flag of Pindamonhangaba Flag of Quaraí Flag of Rio Claro, Rio de Janeiro Flag of Tefé Queen's Personal New Zealand Flag (1962–2022) Flag of

3230-408: 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

3325-582: The German East Africa Company of 1885–1920, which included a constellation of five white five-pointed Crux "stars" on a red ground, later served as the model for symbolism associated with generic German colonial-oriented organisations: the Reichskolonialbund of 1936–1943 and the Friends of the former German Protectorates  [ de ] (1956/1983 to the present). Southern Cross station

3420-528: The Pampas and Patagonia . Alpha and Beta Centauri are of similar declinations (thus distance from the pole) and are often referred as the "Southern Pointers" or just "The Pointers", allowing people to easily identify the Southern Cross, the constellation of Crux. Very few bright stars lie between Crux and the pole itself, although the constellation Musca is fairly easily recognised immediately south of Crux. Down to apparent magnitude +2.5 are 92 stars that shine

3515-734: The Scorpius–Centaurus association , the nearest OB association to the Sun . They are among the highest-mass stellar members of the Lower Centaurus–Crux subgroup of the association, with ages of roughly 10 to 20 million years. Other members include the blue-white stars Zeta , Lambda and both the components of the visual double star , Mu . Crux contains many variable stars . It boasts four Cepheid variables that may all reach naked eye visibility. Other well studied variable stars includes: The star HD 106906 has been found to have

3610-641: The Solomon Islands saw several figures in the Southern Cross. These included a knee protector and a net used to catch Palolo worms . Neighboring peoples in the Marshall Islands saw these stars as a fish. Peninsular Malays also see the likeness of a fish in the Crux, particularly the Scomberomorus or its local name Tohok . Open cluster An open cluster is a type of star cluster made of tens to

3705-492: 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

3800-663: 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

3895-660: 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

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3990-542: 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 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

4085-541: The Australian Eureka Flag . The constellation was also used on the dark blue, shield-like patch worn by personnel of the U.S. Army's Americal Division , which was organized in the Southern Hemisphere, on the island of New Caledonia , and also on the blue diamond of the U.S. 1st Marine Division , which fought on the Southern Hemisphere islands of Guadalcanal and New Britain . The Petersflagge flag of

4180-592: The Confederate States of America in the American Civil War . This list is an incomplete list and some of the flags in this list might not have official status. Flag proportions may vary between the different flags, and sometimes even vary between different versions of the same flag. Presidential Standard of Brazil Vice Presidential Standard of Brazil Flag of the Minister of Defense of Brazil Flag of

4275-747: The Cross shines"). The Southern Cross is mentioned in the Australian National Anthem , " Beneath our radiant Southern Cross we'll toil with hearts and hands " The Southern Cross features in the coat of arms of William Birdwood, 1st Baron Birdwood , the British officer who commanded the Australian and New Zealand Army Corps during the Gallipoli Campaign of the First World War . The Southern Cross

4370-413: 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 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

4465-403: 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

4560-502: 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 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

4655-598: The Pointers are its rope. In Tonga it is known as Toloa ("duck"); it is depicted as a duck flying south, with one of his wings ( δ Crucis ) wounded because Ongo tangata ("two men", α and β Centauri ) threw a stone at it. The Coalsack is known as Humu (the " triggerfish "), because of its shape. In Samoa the constellation is called Sumu ("triggerfish") because of its rhomboid shape, while α and β Centauri are called Luatagata (Two Men), just as they are in Tonga. The peoples of

4750-567: The Portuguese monarch. Explorer Amerigo Vespucci seems to have observed not only the Southern Cross but also the neighboring Coalsack Nebula on his second voyage in 1501–1502. Another early modern description clearly describing Crux as a separate constellation is attributed to Andrea Corsali , an Italian navigator who from 1515 to 1517 sailed to China and the East Indies in an expedition sponsored by King Manuel I . In 1516, Corsali wrote

4845-848: 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 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

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4940-466: The Southern Cross on exiting the Gambia River in 1455, calling it the carro dell'ostro ("southern chariot"). However, Cadamosto's accompanying diagram was inaccurate. Historians generally credit João Faras for being the first European to depict it correctly. Faras sketched and described the constellation (calling it " las guardas ") in a letter written on the beaches of Brazil on 1 May 1500 to

5035-495: The Southern Cross" is a song released by Black Sabbath in 1981. The song was released on the album " Mob Rules ". The Order of the Southern Cross is a Brazilian order of chivalry awarded to "those who have rendered significant service to the Brazilian nation". In " O Sweet Saint Martin's Land ", the lyrics mention the Southern Cross: Thy Southern Cross the night . A stylized version of Crux appears on

5130-412: 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

5225-425: The asterism are Alpha, Beta, Gamma, and Delta Crucis. There is also a fifth star, that is often included with the Southern Cross. There are several other naked-eye stars within the borders of Crux, especially: Unusually, a total of 15 of the 23 brightest stars in Crux are spectrally blue-white B-type stars. Among the five main bright stars, Delta, and probably Alpha and Beta, are likely co-moving B-type members of

5320-517: The brightest as viewed from the Earth . Three of these stars are in Crux making it the most densely populated as to those stars (this being 3.26% of these 92 stars, and in turn being 19.2 times more than the expected 0.17% that would result on a homogenous distribution of all bright stars and a randomised drawing of all 88 constellations, given its area, 0.17% of the sky). Within the constellation's borders, there are 49 stars brighter than or equal to apparent magnitude 6.5. The four main stars that form

5415-408: The brightest. The three other stars of the cross appear clockwise and in order of lessening magnitude: β Crucis (Mimosa), γ Crucis (Gacrux), and δ Crucis (Imai). ε Crucis (Ginan) also lies within the cross asterism. Many of these brighter stars are members of the Scorpius–Centaurus association , a large but loose group of hot blue-white stars that appear to share common origins and motion across

5510-499: 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 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

5605-445: The cloud can reach conditions where they become unstable against collapse. The collapsing cloud region will undergo hierarchical fragmentation into ever smaller clumps, including 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

5700-450: 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

5795-547: The constellation, as adopted by the International Astronomical Union in 1922, is "Cru". The official constellation boundaries, as set by Belgian astronomer Eugène Delporte in 1930, are defined by a polygon of four segments. In the equatorial coordinate system , the right ascension coordinates of these borders lie between 11 56.13 and 12 57.45 , while the declination coordinates are between −55.68° and −64.70°. Its totality figures at least part of

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5890-566: 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

5985-532: The efforts of astronomers. Hundreds of open clusters were listed in the New General Catalogue , first published in 1888 by 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

6080-580: The flags of the Australian state of Victoria , the Australian Capital Territory , the Northern Territory , as well as the flag of Magallanes Region of Chile , the flag of Londrina (Brazil) and several Argentine provincial flags and emblems (for example, Tierra del Fuego and Santa Cruz ). The flag of the Mercosur trading zone displays the four brightest stars. Crux also appears on

6175-456: The former depicting it on his celestial globe and the latter in one of the small celestial maps on his large wall map. Both authors, however, depended on unreliable sources and placed Crux in the wrong position. Crux was first shown in its correct position on the celestial globes of Petrus Plancius and Jodocus Hondius in 1598 and 1600. Its stars were first catalogued separately from Centaurus by Frederick de Houtman in 1603. The constellation

6270-491: 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

6365-433: The gas in the cloud core forms stars, the process of residual gas expulsion is highly damaging to 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

6460-570: The governor-general Flag of Niue Flag of Tokelau New Zealand Red Ensign Royal New Zealand Navy Ensign New Zealand Civil Air Ensign New Zealand Police Ensign Burgee of the Royal New Zealand Yacht Squadron Ensign of the Royal New Zealand Yacht Squadron Crux Blue-white α Crucis (Acrux) is the most southerly member of the constellation and, at magnitude 0.8,

6555-488: The handle and the four stars as the left hand of Tagai, and the stars of Musca as the trident of the fishing spear he is holding. In Aranda traditions of central Australia, the four Cross stars are the talon of an eagle and Gamma Centauri as its leg. Various peoples in the East Indies and Brazil viewed the four main stars as the body of a ray. In both Indonesia and Malaysia, it is known as Bintang Pari and Buruj Pari , respectively ("ray stars"). This aquatic theme

6650-400: The horizon throughout most of Europe. Dante may have known about the constellation in the 14th century, as he describes an asterism of four bright stars in the southern sky in his Divine Comedy . His description, however, may be allegorical, and the similarity to the constellation a coincidence. The 15th century Venetian navigator Alvise Cadamosto made note of what was probably

6745-504: 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

6840-516: 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 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

6935-436: 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

7030-493: The middle of the constellation. However, by the year 14,000, Crux will be visible for most parts of Europe and the continental United States. Its visibility will extend to North Europe by the year 18,000 when it will be less than 30 degrees south declination. In the Southern Hemisphere , the Southern Cross is frequently used for navigation in much the same way that Polaris is used in the Northern Hemisphere . Projecting

7125-431: 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

7220-417: 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 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

7315-495: 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

7410-621: The patterns of stars) in several Aboriginal cultures , while Crux itself is said to be a possum sitting in a tree ( Boorong people of the Wimmera region of northwestern Victoria), a representation of the sky deity Mirrabooka ( Quandamooka people of Stradbroke Island ), a stingray ( Yolngu people of Arnhem Land ), or an eagle ( Kaurna people of the Adelaide Plains ). Two Pacific constellations also included Gamma Centauri . Torres Strait Islanders in modern-day Australia saw Gamma Centauri as

7505-436: 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

7600-551: 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

7695-660: 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

7790-426: The shape of the constellation was like that of a raking hut . The Southern Cross ( α , β , γ and δ Crucis ) together with μ Crucis is one of the asterisms used by Bugis sailors for navigation, called bintoéng bola képpang , meaning "incomplete house star" The Māori name for the Southern Cross is Māhutonga and it is thought of as the anchor ( Te Punga ) of Tama-rereti's waka (the Milky Way ), while

7885-415: The sky but preferentially towards the center of the Milky Way . The other type consisted of a generally sparser population of stars in 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 ,

7980-490: The sky. Crux is sometimes confused with the nearby False Cross asterism by stargazers. The False Cross consists of stars in Carina and Vela, is larger and dimmer, does not have a fifth star, and lacks the two prominent nearby "Pointer Stars". Between the two is the even larger and dimmer Diamond Cross . Crux is easily visible from the southern hemisphere , south of 35th parallel at practically any time of year as circumpolar. It

8075-579: The southern Milky Way. Crux contains four Cepheid variables , each visible to the naked eye under optimum conditions. Crux also contains the bright and colourful open cluster known as the Jewel Box (NGC 4755) on its eastern border. Nearby to the southeast is a large dark nebula spanning 7° by 5° known as the Coalsack Nebula , portions of which are mapped in the neighbouring constellations of Centaurus and Musca . The bright stars in Crux were known to

8170-449: 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

8265-582: 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 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

8360-454: 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

8455-465: 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 the Pleiades , the Hyades and the Alpha Persei Cluster , are visible with the naked eye. Some others, such as

8550-750: 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

8645-501: 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

8740-472: 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,

8835-400: The year south of the 25th parallel north . In tropical regions Crux can be seen in the sky from April to June. Crux is exactly opposite to Cassiopeia on the celestial sphere, and therefore it cannot appear in the sky with the latter at the same time. In this era, south of Cape Town , Adelaide , and Buenos Aires (the 34th parallel south ), Crux is circumpolar and thus always appears in

8930-405: 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 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

9025-475: Was later adopted by Jakob Bartsch in 1624 and Augustin Royer in 1679. Royer is sometimes wrongly cited as initially distinguishing Crux. Crux is bordered by the constellations Centaurus (which surrounds it on three sides) on the east, north and west, and Musca to the south. Covering 68 square degrees and 0.165% of the night sky, it is the smallest of the 88 constellations. The three-letter abbreviation for

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