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A number of recreation activities occur in and around the dam and catchment area . Canning Dam features a number of picnic areas ( with gas barbecues ) , look outs and historic walks โ many with disabled access . Bushwalking occurs throughout the catchment , particularly along the Bibbulmun Track , which passes through the catchment about 10 km upstream of Canning Dam . Several mountain bike trails run either through the Canning National Park or adjacent State Forest areas . |
The Canning Reservoir , Canning River and tributaries are illegally fished for marron , especially during summer . Boating , fishing and swimming are prohibited in the reservoir for health and hygiene reasons . Unauthorised camping ( including overnight stays and / or outside of designated areas ) and unauthorised trail establishment occur more and more frequently in the Canning catchment . |
= = Gallery = = |
= Midge ( Barbie ) = |
Midge Hadley is a fictional doll character in the Barbie line of toys by Mattel that was first released in 1963 . Midge was created , along with Skipper , to counteract criticism that claimed Barbie was a sex symbol . She was marketed as Barbie 's best friend . No Midge dolls were sold for the rest of the vintage years after the 1960s . |
Midge was re @-@ introduced in 1988 as part of the play line , though two vintage reproduction dolls were made specifically for collectors in 1993 and 1998 . The dolls sold in this time period usually had red hair , often with freckles , and her eye color was usually blue . Also in the period , Wedding Day Midge was sold , with the groom being Alan Sherwood , who had been marketed as Midge 's boyfriend in the vintage years . Midge and Alan had three children introduced named Ryan , Nikki , and Cassandra . They also had twins who were never introduced . This was known as the Happy Family line , and in the set , Midge was sold " pregnant " with Nikki as a newborn baby . The Happy Family product became the subject of controversy when some parents disliked the " pregnant " Midge toy because they believed that Midge was too young to have children . |
In 2013 Mattel decided to revamp Midge 's history , reintroducing her as a best friend of Barbie 's , but unmarried , without children , and with no connection to Alan . |
= = Vintage years = = |
When Barbie first came out , she was the subject of a lot of criticism , some of which that claimed Barbie was too mature @-@ looking for children . Midge was the first same @-@ size friend of Barbie ever sold , and was created to oppose these controversies aimed at Barbie . She had a fuller , gentler face mold that was less sexually intimidating , although her body proportions were the same as Barbie and they both stood at 11 1 โ 2 inches ( 290 mm ) tall . This allowed the two dolls to be able to share clothes and accessories . Her head mold was stamped " 1958 " , the same as Barbie . When Midge arrived , the markings on the straight leg body mold they shared changed to include both her and Barbie . Midge had shoulder @-@ length hair that flipped at the ends . Buyers had an option of buying a doll with one of three different hair colors : red , blond , or brunette . Her face was usually brushed with freckles . The dolls that were sold without freckles had a longer hair style and are now hard to find . Depending on the doll 's hair color , the color of her two @-@ piece swimming suit varied . If Midge had red hair her swimsuit was yellow and orange , for blond hair it was in two shades of blue , and if she was brunette it was pink and red . The first vintage Midge dolls had a value of $ 175 MIB ( Mint In Box ) in 2007 . |
For the first two years that Midge was sold , she had " straight legs " that could not bend at the knee . A rare Midge with teeth was sold the first year and is now sought after by collectors . One year later , in 1964 the dolls that were sold had slightly longer hair . Midge 's boyfriend Allan arrived as well . Early in 1965 , Wigs Wardrobe Midge was sold , and consisted of a Midge head with short molded hair and three wigs . This was the Midge counterpart of the Fashion Queen Barbie . Since she came with only a head , another doll had to provide for the body . In 1965 Midge with bendable legs was introduced . She had shorter " bobbed " hair , like the American Girl Barbie , with a blue headband . Her swimming suit was different as well , and was now one @-@ piece and striped . |
= = Return = = |
From her introduction to until 1967 , Midge was marketed as Barbie 's original best friend , but no dolls were sold for about 20 years until 1988 , when California Dream Midge was sold as part of a beach line , which used the " Steffie " mold . The same " Steffie " mold was used for Cool Times Midge in 1989 . In 1990 , she began to use the " Diva " mold for All Stars Midge and The Beat Midge . In 1991 she was married to Allan ( now spelled " Alan " ) . Before and after the Wedding Day Midge doll was sold , many Midge play line dolls were produced . Before Wedding Day Midge , Midge dolls still had freckles , but up until Hawaii Midge was sold in 1999 , the dolls lacked freckles . Most of the dolls were red @-@ haired with blue or green eyes , but some dolls were brunette . The most commonly used head mold for Midge in this period was the " Diva " mold , stamped 1985 . |
A 35th anniversary Midge reproduction doll was sold in 1998 for collectors , made to look like the vintage Midge dolls . She had red hair , was dressed in her original orange and lime two @-@ piece swimming suit , and came with a reproduction of the Senior Prom outfit from 1964 โ 1965 as well as a reproduction of the box the Midge dolls originally came in . Earlier in 1993 , for Midge 's 30th anniversary , a Midge reproduction doll was also produced , but she did not possess a reproduction of her original swimsuit or the original box . Like the later version , she came in a reproduction of the Senior Prom outfit . |
In 2013 , Midge appeared on the webseries Barbie : Life in the Dreamhouse where it is revealed that she has moved to Malibu . With this , her canon has been changed extensively , and she is a teenager who is retro at heart and still uses old @-@ fangled terms . The whole ' Happy Family ' canon has been dropped altogether due to controversy . Two Midge dolls will be released in 2013 - one is as part of a collectors set with Barbie , and the other on her own in the Life in the Dreamhouse doll line . |
= = " Happy Family " line = = |
The year after Midge and Alan were married , a picture of the couple with twin babies was shown in a pamphlet , but the dolls were never produced . However , in 2003 , she and Alan were re @-@ introduced with a family consisting of them and three different kids , three @-@ year @-@ old Ryan , and newborn baby Nikki . This was known as the " Happy Family " line , and was similar to the discontinued Heart Family line of the 1980s . The dolls came in both European American and African American versions . This was the first time an African American Midge was ever produced . |
Midge was sold " pregnant " with Nikki , who was a tiny baby inside Midge 's magnetic removable womb . This led to some controversy with some consumers saying that the doll was inappropriate for children , or that it promoted teen pregnancy . Another cause for this controversy was that Midge did not initially have a wedding ring , but this was later fixed . She also was packaged without Alan . Customers complaining about the doll led to Wal @-@ Mart pulling the Happy Family line off their shelves . A new version of this Midge was produced for Wal @-@ Mart , this time not pregnant and with a cardboard cut @-@ out display of Alan and Ryan standing next to her inside the box . The Happy Family Line included everything from a talking house , a backyard swimming pool , neighborhood market , and playground . |
Later , around Nikki 's first birthday , Midge was " pregnant " again with another child , who wasn 't named or given a specific gender , as the gender was a surprise when the owner opened the doll 's box . Midge 's new baby was later named Cassandra . Midge has two known parents who are simply called " Grandpa " and " Grandma " . At first , the grandparent dolls were sold together as part of a big set consisting of the dolls and a kitchen play set , but for Nikki 's first birthday they were sold separately . Midge , Alan , and Ryan gave Nikki a dog for her birthday . They too came in both Caucasian and African American versions . They use different body molds , to reflect their age . |
= = Head Molds = = |
Midge 's first appearance was made with her own headmold , Vintage Midge |
Later , we have Midge using DIVA ( by Barbie and the Rockers ) headmold |
Before Teresa made her debut , Midge used Steffie headmold |
Midge comes and goes so many times , but with her 50th birthday , she returns with the Steffie headmold |
Florida Midge uses Mackie headmold . |
= The Tempest ( album ) = |
The Tempest is the tenth studio album by American hip hop duo Insane Clown Posse . Released in 2007 , the album marks the return of producer Mike E. Clark , who had a falling @-@ out with the duo in 2000 . However , he did not collaborate directly with ICP , and would not do so until their 2009 album Bang ! Pow ! Boom ! |
The album 's concept compares a violent storm to a roller coaster ; its lyrical themes vary from horrorcore @-@ based character deconstructions and songs about the supernatural to humorous and lighter subject matter . Clark 's production was praised by critics , and the album peaked at # 20 on the Billboard 200 . It is the group 's 23rd overall release . |
= = History = = |
Mike E. Clark produced much of Insane Clown Posse 's discography , as well as working with other groups on Psychopathic Records , until having a falling @-@ out with ICP in 2000 , after completing ICP 's album 's Bizaar and Bizzar , and beginning production on the Dark Lotus debut album Tales from the Lotus Pod . |
After becoming a full @-@ time producer for Kid Rock , Clark contracted pneumonia , but ignored the illness , and began coughing severely as he awoke , leading to a three @-@ month stay in Mount Clemens General Hospital , during which one of his lungs collapsed three times . As the result of his near @-@ death experience , Clark decided to reconcile with Bruce and Utsler . Phone conversations between Clark and Insane Clown Posse led to Clark producing Shaggy 2 Dope 's 2006 solo album F.T.F.O .. The following year , Clark produced The Tempest ; however , in both instances , he did not work with Psychopathic Records directly . Because of this , ICP felt that The Tempest was missing the collaborative element that they felt made their earlier albums enjoyable . Clark would not work directly work with Psychopathic Records until 2009 's Bang ! Pow ! Boom ! |
= = Music and lyrics = = |
Unlike previous Insane Clown Posse albums , The Tempest is not connected to the Dark Carnival mythology , which formed the basis for ICP 's " Joker 's Cards " series , which began in 1992 with Carnival of Carnage and concluded with the albums The Wraith : Shangri @-@ La and Hell 's Pit ; however , it references themes , concepts and songs from previous albums . Joseph Bruce ( Violent J ) said that The Tempest is a concept album in its own right . Bruce describes the album 's concept as relating to both a violent storm which turns into a tornado and pulls people into a hurricane as well as a roller coaster . According to Bruce , " That 's a lot like riding on a violent roller coaster , I 'd assume . You get jerked to the left , jerked to the right , sucked way up into the sky , and then you go shooting down to the floor , and then you jerk up to the left and then you whip around to the right . Well , The Tempest is a storm in the form of a roller coaster . " As a result of this concept , the album focuses on a variety of different moods . |
The Tempest maintains much of the horrorcore lyrical content ICP is known for , as well as their humorous perspective . Unlike previous albums , this album does not contain any disses aimed at other rappers or music industry figures . Bruce and Joseph Utsler ( Shaggy 2 Dope ) ' s rapping on this album is described by Allmusic reviewer David Jeffries as being delivered in " a carnival barker fashion that fits with their circus motif " , and contrasted Bruce and Utsler themselves as being like " Alice Cooper with a mallrat attitude " . |
The lyrics of " Growing Again " , which describes Violent J growing into a giant , were inspired by Bruce 's weight gain ; Bruce also says that the song reflects the feeling of being able to " rap about anything we want [ ... ] I feel we have the right for some songs to be softer and not about killing or Dark Carnival . " " The Tower " describes a war veteran and expert marksman climbing a college tower and shooting people with an arsenal of weapons , a reference to Charles Whitman 's 1966 murder spree . |
Mike E. Clark 's production incorporates elements of rock and heavy metal , as well as live instrumentation . Reviewer Lana Cooper of PopMatters compares " Ride the Tempest " to Flock of Seagulls , and describes the instrumentation as incorporating elements of synthesizers and calliope . Cooper says that " Growing Again " incorporates power ballad chords . Jeffries describes " I Do This ! " as being influenced by psychedelia , and called " Mexico City " " Low Rider music " . |
= = Release and reception = = |
The album was released with a bonus poster . The Tempest debuted at # 20 on the U.S. Billboard 200 , selling about 33 @,@ 000 copies in its first week . Reviews from Allmusic and PopMatters generally appraised Mike E. Clark 's production as the album 's most appealing element . Allmusic 's David Jeffries wrote , " there 's no denying that Clark 's vision does wonders for the duo . " PopMatters ' Lana Cooper said that " [ Insane Clown Posse 's ] theatrics have to be given their due . " |
= = Track listing = = |
= = Chart positions = = |
= = Personnel = = |
Joseph Bruce โ vocals , composer |
Shaggy 2 Dope โ vocals , scratching |
Mike E. Clark โ composer , engineer , mixing , producer , programming |
Jeffrey Campo โ mastering |
Brian Debler โ artwork , cover design |
DJ Clay โ scratching , vocals |
Insane Clown Posse โ composer , vocals |
James Mitchell โ vocals |
The R.O.C. โ vocals , background vocals |
Razor Ray โ guitar , soloist , vocals , background vocals |
Michael Scotta โ artwork , cover design |
Cindy Wulkan โ artwork , cover design |
= Star = |
A star is a luminous sphere of plasma held together by its own gravity . The nearest star to Earth is the Sun . Many other stars are visible to the naked eye from Earth during the night , appearing as a multitude of fixed luminous points in the sky due to their immense distance from Earth . Historically , the most prominent stars were grouped into constellations and asterisms , the brightest of which gained proper names . Astronomers have assembled star catalogues that identify the known stars and provide standardized stellar designations . However , most of the stars in the Universe , including all stars outside our galaxy , the Milky Way , are invisible to the naked eye from Earth . Indeed , most are invisible from Earth even through the most powerful telescopes . |
For at least a portion of its life , a star shines due to thermonuclear fusion of hydrogen into helium in its core , releasing energy that traverses the star 's interior and then radiates into outer space . Almost all naturally occurring elements heavier than helium are created by stellar nucleosynthesis during the star 's lifetime , and for some stars by supernova nucleosynthesis when it explodes . Near the end of its life , a star can also contain degenerate matter . Astronomers can determine the mass , age , metallicity ( chemical composition ) , and many other properties of a star by observing its motion through space , its luminosity , and spectrum respectively . The total mass of a star is the main factor that determines its evolution and eventual fate . Other characteristics of a star , including diameter and temperature , change over its life , while the star 's environment affects its rotation and movement . A plot of the temperature of many stars against their luminosities produces a plot known as a Hertzsprung โ Russell diagram ( H โ R diagram ) . Plotting a particular star on that diagram allows the age and evolutionary state of that star to be determined . |
A star 's life begins with the gravitational collapse of a gaseous nebula of material composed primarily of hydrogen , along with helium and trace amounts of heavier elements . When the stellar core is sufficiently dense , hydrogen becomes steadily converted into helium through nuclear fusion , releasing energy in the process . The remainder of the star 's interior carries energy away from the core through a combination of radiative and convective heat transfer processes . The star 's internal pressure prevents it from collapsing further under its own gravity . When the hydrogen fuel at the core is exhausted , a star of mass 0 @.@ 4 times greater than the Sun 's will expand to become a red giant . In some cases , it will fuse heavier elements at the core or in shells around the core . As the star expands it throws a part of its mass , enriched with those heavier elements , into the interstellar environment , to be recycled later as new stars . Meanwhile , the core becomes a stellar remnant : a white dwarf , a neutron star , or if it is sufficiently massive a black hole . |
Binary and multi @-@ star systems consist of two or more stars that are gravitationally bound and generally move around each other in stable orbits . When two such stars have a relatively close orbit , their gravitational interaction can have a significant impact on their evolution . Stars can form part of a much larger gravitationally bound structure , such as a star cluster or a galaxy . |
= = Observation history = = |
Historically , stars have been important to civilizations throughout the world . They have been part of religious practices and used for celestial navigation and orientation . Many ancient astronomers believed that stars were permanently affixed to a heavenly sphere and that they were immutable . By convention , astronomers grouped stars into constellations and used them to track the motions of the planets and the inferred position of the Sun . The motion of the Sun against the background stars ( and the horizon ) was used to create calendars , which could be used to regulate agricultural practices . The Gregorian calendar , currently used nearly everywhere in the world , is a solar calendar based on the angle of the Earth 's rotational axis relative to its local star , the Sun . |
The oldest accurately dated star chart was the result of ancient Egyptian astronomy in 1534 BC . The earliest known star catalogues were compiled by the ancient Babylonian astronomers of Mesopotamia in the late 2nd millennium BC , during the Kassite Period ( ca . 1531 โ 1155 BC ) . |
The first star catalogue in Greek astronomy was created by Aristillus in approximately 300 BC , with the help of Timocharis . The star catalog of Hipparchus ( 2nd century BC ) included 1020 stars , and was used to assemble Ptolemy 's star catalogue . Hipparchus is known for the discovery of the first recorded nova ( new star ) . Many of the constellations and star names in use today derive from Greek astronomy . |
In spite of the apparent immutability of the heavens , Chinese astronomers were aware that new stars could appear . In 185 AD , they were the first to observe and write about a supernova , now known as the SN 185 . The brightest stellar event in recorded history was the SN 1006 supernova , which was observed in 1006 and written about by the Egyptian astronomer Ali ibn Ridwan and several Chinese astronomers . The SN 1054 supernova , which gave birth to the Crab Nebula , was also observed by Chinese and Islamic astronomers . |
Medieval Islamic astronomers gave Arabic names to many stars that are still used today and they invented numerous astronomical instruments that could compute the positions of the stars . They built the first large observatory research institutes , mainly for the purpose of producing Zij star catalogues . Among these , the Book of Fixed Stars ( 964 ) was written by the Persian astronomer Abd al @-@ Rahman al @-@ Sufi , who observed a number of stars , star clusters ( including the Omicron Velorum and Brocchi 's Clusters ) and galaxies ( including the Andromeda Galaxy ) . According to A. Zahoor , in the 11th century , the Persian polymath scholar Abu Rayhan Biruni described the Milky Way galaxy as a multitude of fragments having the properties of nebulous stars , and also gave the latitudes of various stars during a lunar eclipse in 1019 . |
According to Josep Puig , the Andalusian astronomer Ibn Bajjah proposed that the Milky Way was made up of many stars that almost touched one another and appeared to be a continuous image due to the effect of refraction from sublunary material , citing his observation of the conjunction of Jupiter and Mars on 500 AH ( 1106 / 1107 AD ) as evidence . Early European astronomers such as Tycho Brahe identified new stars in the night sky ( later termed novae ) , suggesting that the heavens were not immutable . In 1584 Giordano Bruno suggested that the stars were like the Sun , and may have other planets , possibly even Earth @-@ like , in orbit around them , an idea that had been suggested earlier by the ancient Greek philosophers , Democritus and Epicurus , and by medieval Islamic cosmologists such as Fakhr al @-@ Din al @-@ Razi . By the following century , the idea of the stars being the same as the Sun was reaching a consensus among astronomers . To explain why these stars exerted no net gravitational pull on the Solar System , Isaac Newton suggested that the stars were equally distributed in every direction , an idea prompted by the theologian Richard Bentley . |
The Italian astronomer Geminiano Montanari recorded observing variations in luminosity of the star Algol in 1667 . Edmond Halley published the first measurements of the proper motion of a pair of nearby " fixed " stars , demonstrating that they had changed positions since the time of the ancient Greek astronomers Ptolemy and Hipparchus . |
William Herschel was the first astronomer to attempt to determine the distribution of stars in the sky . During the 1780s he established a series of gauges in 600 directions and counted the stars observed along each line of sight . From this he deduced that the number of stars steadily increased toward one side of the sky , in the direction of the Milky Way core . His son John Herschel repeated this study in the southern hemisphere and found a corresponding increase in the same direction . In addition to his other accomplishments , William Herschel is also noted for his discovery that some stars do not merely lie along the same line of sight , but are also physical companions that form binary star systems . |
The science of stellar spectroscopy was pioneered by Joseph von Fraunhofer and Angelo Secchi . By comparing the spectra of stars such as Sirius to the Sun , they found differences in the strength and number of their absorption lines โ the dark lines in a stellar spectra caused by the atmosphere 's absorption of specific frequencies . In 1865 Secchi began classifying stars into spectral types . However , the modern version of the stellar classification scheme was developed by Annie J. Cannon during the 1900s . |
The first direct measurement of the distance to a star ( 61 Cygni at 11 @.@ 4 light @-@ years ) was made in 1838 by Friedrich Bessel using the parallax technique . Parallax measurements demonstrated the vast separation of the stars in the heavens . Observation of double stars gained increasing importance during the 19th century . In 1834 , Friedrich Bessel observed changes in the proper motion of the star Sirius and inferred a hidden companion . Edward Pickering discovered the first spectroscopic binary in 1899 when he observed the periodic splitting of the spectral lines of the star Mizar in a 104 @-@ day period . Detailed observations of many binary star systems were collected by astronomers such as William Struve and S. W. Burnham , allowing the masses of stars to be determined from computation of orbital elements . The first solution to the problem of deriving an orbit of binary stars from telescope observations was made by Felix Savary in 1827 . The twentieth century saw increasingly rapid advances in the scientific study of stars . The photograph became a valuable astronomical tool . Karl Schwarzschild discovered that the color of a star and , hence , its temperature , could be determined by comparing the visual magnitude against the photographic magnitude . The development of the photoelectric photometer allowed precise measurements of magnitude at multiple wavelength intervals . In 1921 Albert A. Michelson made the first measurements of a stellar diameter using an interferometer on the Hooker telescope at Mount Wilson Observatory . |
Important theoretical work on the physical structure of stars occurred during the first decades of the twentieth century . In 1913 , the Hertzsprung @-@ Russell diagram was developed , propelling the astrophysical study of stars . Successful models were developed to explain the interiors of stars and stellar evolution . Cecilia Payne @-@ Gaposchkin first proposed that stars were made primarily of hydrogen and helium in her 1925 PhD thesis . The spectra of stars were further understood through advances in quantum physics . This allowed the chemical composition of the stellar atmosphere to be determined . |
With the exception of supernovae , individual stars have primarily been observed in the Local Group , and especially in the visible part of the Milky Way ( as demonstrated by the detailed star catalogues available for our galaxy ) . But some stars have been observed in the M100 galaxy of the Virgo Cluster , about 100 million light years from the Earth . In the Local Supercluster it is possible to see star clusters , and current telescopes could in principle observe faint individual stars in the Local Group ( see Cepheids ) . However , outside the Local Supercluster of galaxies , neither individual stars nor clusters of stars have been observed . The only exception is a faint image of a large star cluster containing hundreds of thousands of stars located at a distance of one billion light years โ ten times further than the most distant star cluster previously observed . |
= = Designations = = |
The concept of a constellation was known to exist during the Babylonian period . Ancient sky watchers imagined that prominent arrangements of stars formed patterns , and they associated these with particular aspects of nature or their myths . Twelve of these formations lay along the band of the ecliptic and these became the basis of astrology . Many of the more prominent individual stars were also given names , particularly with Arabic or Latin designations . |
As well as certain constellations and the Sun itself , individual stars have their own myths . To the Ancient Greeks , some " stars " , known as planets ( Greek ฯฮปฮฑฮฝฮฎฯฮทฯ ( planฤtฤs ) , meaning " wanderer " ) , represented various important deities , from which the names of the planets Mercury , Venus , Mars , Jupiter and Saturn were taken . ( Uranus and Neptune were also Greek and Roman gods , but neither planet was known in Antiquity because of their low brightness . Their names were assigned by later astronomers . ) |
Circa 1600 , the names of the constellations were used to name the stars in the corresponding regions of the sky . The German astronomer Johann Bayer created a series of star maps and applied Greek letters as designations to the stars in each constellation . Later a numbering system based on the star 's right ascension was invented and added to John Flamsteed 's star catalogue in his book " Historia coelestis Britannica " ( the 1712 edition ) , whereby this numbering system came to be called Flamsteed designation or Flamsteed numbering . |
The only internationally recognized authority for naming celestial bodies is the International Astronomical Union ( IAU ) . A number of private companies sell names of stars , which the British Library calls an unregulated commercial enterprise . The IAU has disassociated itself from this commercial practice , and these names are neither recognized by the IAU nor used by them . One such star @-@ naming company is the International Star Registry , which , during the 1980s , was accused of deceptive practice for making it appear that the assigned name was official . This now @-@ discontinued ISR practice was informally labeled a scam and a fraud , and the New York City Department of Consumer Affairs issued a violation against ISR for engaging in a deceptive trade practice . |
= = Units of measurement = = |
Although stellar parameters can be expressed in SI units or CGS units , it is often most convenient to express mass , luminosity , and radii in solar units , based on the characteristics of the Sun : |
Large lengths , such as the radius of a giant star or the semi @-@ major axis of a binary star system , are often expressed in terms of the astronomical unit โ approximately equal to the mean distance between the Earth and the Sun ( 150 million km or 93 million miles ) . |
= = Formation and evolution = = |
Stars condense from regions of space of higher density , yet those regions are less dense than within a vacuum chamber . These regions - known as molecular clouds - consist mostly of hydrogen , with about 23 to 28 percent helium and a few percent heavier elements . One example of such a star @-@ forming region is the Orion Nebula . Most stars form in groups of dozens to hundreds of thousands of stars . Massive stars in these groups may powerfully illuminate those clouds , ionizing the hydrogen , and creating H II regions . Such feedback effects , from star formation , may ultimately disrupt the cloud and prevent further star formation . |
All stars spend the majority of their existence as main sequence stars , fueled primarily by the nuclear fusion of hydrogen into helium within their cores . However , stars of different masses have markedly different properties at various stages of their development . The ultimate fate of more massive stars differs from that of less massive stars , as do their luminosities and the impact they have on their environment . Accordingly , astronomers often group stars by their mass : |
Very low mass stars , with masses below 0 @.@ 5 M โ , are fully convective and distribute helium evenly throughout the whole star while on the main sequence . Therefore , they never undergo shell burning , never become red giants , which cease fusing and become helium white dwarfs and slowly cool after exhausting their hydrogen . However , as the lifetime of 0 @.@ 5 M โ stars is longer than the age of the universe , no such star has yet reached the white dwarf stage . |
Low mass stars ( including the Sun ) , with a mass between 0 @.@ 5 M โ and 1 @.@ 8 โ 2 @.@ 5 M โ depending on composition , do become red giants as their core hydrogen is depleted and they begin to burn helium in core in a helium flash ; they develop a degenerate carbon @-@ oxygen core later on the asymptotic giant branch ; they finally blow off their outer shell as a planetary nebula and leave behind their core in the form of a white dwarf . |
Intermediate @-@ mass stars , between 1 @.@ 8 โ 2 @.@ 5 M โ and 5 โ 10 M โ , pass through evolutionary stages similar to low mass stars , but after a relatively short period on the RGB they ignite helium without a flash and spend an extended period in the red clump before forming a degenerate carbon @-@ oxygen core . |
Massive stars generally have a minimum mass of 7 โ 10 M โ ( possibly as low as 5 โ 6 M โ ) . After exhausting the hydrogen at the core these stars become supergiants and go on to fuse elements heavier than helium . They end their lives when their cores collapse and they explode as supernovae . |
= = = Star formation = = = |
The formation of a star begins with gravitational instability within a molecular cloud , caused by regions of higher density - often triggered by compression of clouds by radiation from massive stars , expanding bubbles in the interstellar medium , the collision of different molecular clouds , or the collision of galaxies ( as in a starburst galaxy ) . When a region reaches a sufficient density of matter to satisfy the criteria for Jeans instability , it begins to collapse under its own gravitational force . |
As the cloud collapses , individual conglomerations of dense dust and gas form " Bok globules " . As a globule collapses and the density increases , the gravitational energy converts into heat and the temperature rises . When the protostellar cloud has approximately reached the stable condition of hydrostatic equilibrium , a protostar forms at the core . These pre โ main sequence stars are often surrounded by a protoplanetary disk and powered mainly by the conversion of gravitational energy . The period of gravitational contraction lasts about 10 to 15 million years . |
Early stars of less than 2 M โ are called T Tauri stars , while those with greater mass are Herbig Ae / Be stars . These newly formed stars emit jets of gas along their axis of rotation , which may reduce the angular momentum of the collapsing star and result in small patches of nebulosity known as Herbig โ Haro objects . These jets , in combination with radiation from nearby massive stars , may help to drive away the surrounding cloud from which the star was formed . |
Early in their development , T Tauri stars follow the Hayashi track โ they contract and decrease in luminosity while remaining at roughly the same temperature . Less massive T Tauri stars follow this track to the main sequence , while more massive stars turn onto the Henyey track . |
Most stars are observed to be members of binary star systems , and the properties of those binaries are the result of the conditions in which they formed . A gas cloud must lose its angular momentum in order to collapse and form a star . The fragmentation of the cloud into multiple stars distributes some of that angular momentum . The primordial binaries transfer some angular momentum by gravitational interactions during close encounters with other stars in young stellar clusters . These interactions tend to split apart more widely separated ( soft ) binaries while causing hard binaries to become more tightly bound . This produces the separation of binaries into their two observed populations distributions . |
= = = Main sequence = = = |
Stars spend about 90 % of their existence fusing hydrogen into helium in high @-@ temperature and high @-@ pressure reactions near the core . Such stars are said to be on the main sequence , and are called dwarf stars . Starting at zero @-@ age main sequence , the proportion of helium in a star 's core will steadily increase , the rate of nuclear fusion at the core will slowly increase , as will the star 's temperature and luminosity . The Sun , for example , is estimated to have increased in luminosity by about 40 % since it reached the main sequence 4 @.@ 6 billion ( 4 @.@ 6 ร 109 ) years ago . |
Every star generates a stellar wind of particles that causes a continual outflow of gas into space . For most stars , the mass lost is negligible . The Sun loses 10 โ 14 M โ every year , or about 0 @.@ 01 % of its total mass over its entire lifespan . However , very massive stars can lose 10 โ 7 to 10 โ 5 M โ each year , significantly affecting their evolution . Stars that begin with more than 50 M โ can lose over half their total mass while on the main sequence . |
The time a star spends on the main sequence depends primarily on the amount of fuel it has and the rate at which it fuses it . The Sun 's is expected to live 10 billion ( 1010 ) years . Massive stars consume their fuel very rapidly and are short @-@ lived . Low mass stars consume their fuel very slowly . Stars less massive than 0 @.@ 25 M โ , called red dwarfs , are able to fuse nearly all of their mass while stars of about 1 M โ can only fuse about 10 % of their mass . The combination of their slow fuel @-@ consumption and relatively large usable fuel supply allows low mass stars to last about one trillion ( 1012 ) years ; the most extreme of 0 @.@ 08 M โ ) will last for about 12 trillion years . Red dwarfs become hotter and more luminous as they accumulate helium . When they eventually run out of hydrogen , they contract into a white dwarf and decline in temperature . However , since the lifespan of such stars is greater than the current age of the universe ( 13 @.@ 8 billion years ) , no stars under about 0 @.@ 85 M โ are expected to have moved off the main sequence . |
Besides mass , the elements heavier than helium can play a significant role in the evolution of stars . Astronomers label all elements heavier than helium " metals " , and call the chemical concentration of these elements in a star , its metallicity . A star 's metallicity can influence the time the star takes to burn its fuel , and controls the formation of its magnetic fields , which affects the strength of its stellar wind . Older , population II stars have substantially less metallicity than the younger , population I stars due to the composition of the molecular clouds from which they formed . Over time , such clouds become increasingly enriched in heavier elements as older stars die and shed portions of their atmospheres . |
= = = Post โ main sequence = = = |
As stars of at least 0 @.@ 4 M โ exhaust their supply of hydrogen at their core , they start to fuse hydrogen in a shell outside the helium core . Their outer layers expand and cool greatly as they form a red giant . In about 5 billion years , when the Sun enters the helium burning phase , it will expand to a maximum radius of roughly 1 astronomical unit ( 150 million kilometres ) , 250 times its present size , and lose 30 % of its current mass . |
As the hydrogen shell burning produces more helium , the core increases in mass and temperature . In a red giant of up to 2 @.@ 25 M โ , the mass of the helium core becomes degenerate prior to helium fusion . Finally , when the temperature increases sufficiently , helium fusion begins explosively in what is called a helium flash , and the star rapidly shrinks in radius , increases its surface temperature , and moves to the horizontal branch of the HR diagram . For more massive stars , helium core fusion starts before the core becomes degenerate , and the star spends some time in the red clump , slowly burning helium , before the outer convective envelope collapses and the star then moves to the horizontal branch . |
After the star has fused the helium of its core , the carbon product fuses producing a hot core with an outer shell of fusing helium . The star then follows an evolutionary path called the asymptotic giant branch ( AGB ) that parallels the other described red giant phase , but with a higher luminosity . The more massive AGB stars may undergo a brief period of carbon fusion before the core becomes degenerate . |
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