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Study Notes for Chapter 30: Stars, Galaxies, and the Universe 1 A galaxy is made of stars, dust, and gas bound together by ______. gravity 2 A large, bright star whose hot core has used most of its hydrogen is a _____. giant 3 A light-year is the distance ____ travels in a year. light 4 A small, hot, extremely dense core left after a star collapses is a _____ dwarf. white 5 A star moving away from the Earth has a spectrum that is shifted toward ______. red 6 A star with the sun’s mass would stay on the _____ sequence of the H-R diagram for about 10 billion years. main 7 A white ______ is a hot, extremely dense core of matter left after a star _______. dwarf collapses 8 About ______ stars are visible from Earth without a telescope. 6,000 9 ______ magnitude is the true brightness of a star. Absolute 10 After its temperature rises to 10,000,000°C, a _____ becomes a star when nuclear fusion begins. protostar 11 _______ magnitude is the brightness of a star as it appears from Earth. Apparent 12 Astronomers believe that cosmic background _______ formed shortly after the big bang. radiation 13 By analyzing the light that a star emits, astronomers can determine the ______ and ________ of a star. composition temperature 14 During the main sequence stage, ______ fuses into ______ to generate energy in a star’s core. hydrogen helium 15 Hubble’s discovery that there was ____ shift in the spectra of galaxies lead to an understanding that the universe is ____. red expanding 16 Many astronomers believe that black _____ do not exist. dwarfs 17 Most of the universe is made of _____ energy and dark _______. dark matter 18 Red shift in the spectra of galaxies told ______ that the universe is expanding. Hubble 19 Scientists determine the composition and temperature of stars by analyzing the ________ of the light that stars emit. spectra 20 Stars _____ to move in the sky because ______ is moving. appear Earth 21 The ____ bang occurred about __ billion years ago. big 14 22 The ____ stars are ____ in color, the hottest stars are _____. coolest red blue THE END