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DSST Astronomy notes 1

The magnitude of a variable star changes with time

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The magnitude of a variable star changes with time and is called the “light curve” of that star 98) Pulsating Variable Stars – they periodically expand and contract, affecting size and light a) Largest number of variable stars are pulsating 99) Eruptive Variable Stars – stars that show sudden outbursts of light a) Least common of variable stars 100) Eclipsing Variable Binary Stars whose orbits of mutual revolution are in our line of sight and eclipse each other a) Not true variable stars, but are classified as such because of their luminosity changes during eclipses 101) Novae (plural) or Nova - most famous of the eruptive variable stars a) Nova means “new” – an existing star that suddenly emits an outburst of light b) Ancient times people believed this to be the birth of a new star c) Novae stars remain bright for only a few days or weeks and gradually fade 102) Supernova – a star that flares up to hundreds of millions of times its former brightness 103) Interstellar Dust – clouds of gas and tiny solid particles in space a) Has very high reflecting power, much like snow b) Called a nebula, Latin for clouds c) Grains absorb some light but most is scattered 104) Dark Nebulae – areas of gas and dust can extend over vast regions and greatly dim or completely obscure the light of starts behind them a) Example: the opaque clouds on any photograph of the Milky way b) Earliest catalogues of nebulous appearing objects was prepared in 1781 by Charles Messier 105) Reddening – of starlight by interstellar dust shows that the stars are dimmed a) It is possible to estimate the total amount a star is dimmed from the amount of reddening 106) Polarize Light means to cause it to vibrate in a particular direction or path 107) Star Cluster – a congregation of stars that have a stronger gravitational attraction for each other over other stars a) Can be many stars or only a few 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
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The magnitude of a variable star changes with time and is...

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