Globular cluster a circularly symmetrical system of

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108) Globular Cluster – a circularly symmetrical system of stars with the highest concentration of stars near its own center a) Most famous naked-eye globular cluster is M13 in the constellation of Hercules b) Oldest assemblages of stars in the galaxy c) Estimated anywhere from 10-12 billion years old d) Composed of Population II stars 109) Open Clusters – appear comparatively loose and “open” a) Fewer stars than globular clusters b) Show no concentration of stars toward their own centers c) Lack the high degree of spherical symmetry
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d) Relatively young e) Are brighter and hotter stars f) Some appear irregular 110) Association – a group of stars that do not fall under the category of globular or open cluster stars a) Orion is one of the most well know Association stars 111) Surface Temperature of star determines its brightness and color and its MASS a) More Mass means higher temperature, higher luminosity, bigger a.i) Hottest stars are blue a.ii) Coolest are red b) Mass also determines b.i)the lifetime of a star, b.ii) how much fuel it has to burn, and b.iii) how quickly it will burn (luminosity) 112) Main Sequence Star is a sequence of stars on the Hertzsprung-Russell diagram (H-R diagram) containing the majority of stars and they run diagonally from the upper left to the lower right (a.i.1) About 23,000 stars are plotted on the H-R diagram to show relationship between absolute magnitude, luminosity, classification and the effective temperature b) A star on the main sequence as long as it has enough Hydrogen to burn c) Life of a Main Sequence Star c.i) Becomes a main sequence star once it starts nuclear fusion (c.i.1) Main sequence star is converting hydrogen to helium through nuclear reactions (c.i.2) Left over mass escapes as electromagnetic radiation (light and heat) (c.i.3) Once the hydrogen supply is gone, it leaves the main sequence and becomes a Red Giant 113) Stars are born in Molecular Clouds a) Dense clouds of gas and dust b) Molecular clouds are also referred to as a “Stellar Nursery” c) Usually seen as a nebula of high density 114) Protostar – the stage before becoming an actual star a) Large cool mass of gas b) If it’s too small it may never be a star – instead a Brown Dwarf 115) Nuclear Fusion of Hydrogen– must occur for a protostar to become an actual star a) Must have enough mass to reach 10 million degrees Celsius b) Nuclear fusion begins to turn hydrogen into helium so the protostar can become an actual main sequence star, determined by mass c) Star collapses after the star turns all of the hydrogen in its core into helium d) The core keeps compressing until it reaches a temperature and density that is high enough to begin fusion of helium to form carbon e) Meanwhile the outer layers are expanding rapidly f) Result is a bigger star with a smaller core – Red Giant f.i) Red because its cooler than a main sequence star, but due to its size, its more luminous 116) Summary- a.i) The hydrogen in a molecule cloud collapses to form a weakly glowing protostar.
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