96 variable stars stars that vary in light a are

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96) Variable Stars – stars that vary in light a) Are designated in order of time of discovery in the constellation in which they occur b) Once discovered they are named by a letter followed by the constellation where it appears 97) Variables of Star Brightness a) Estimating the magnitude of the variable by visual observation through a telescope b) Comparing the magnitude to the variable star to other stars c) Determining the magnitude of the star by photoelectric photometry d) 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 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
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