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Unformatted text preview: RR Lyraes: all have same luminosity (about 100x sun) Range good to about 100 kpc Visible portion of our galactic disc is 30 kpc across, light takes 100,000 years to get across Cepheid: luminosity is neatly correlated to pulsation period Much greater range: 25 mega pcs Andromeda (nearest galaxy) is about 0.8 mpc away Globs sun not at center of our galaxy Galaxtic mass: Velocity of a circular objects = (GM <r / r) M <r = rV c 2 / G Mass within 8 kpc =~ 10 11 solar masses Mass within 15 kpc = ~ 2 x 10 11 solar masses Due to information about rotation speed, keplerian motion, distance from galactic center, there must be extra mass than what we see dark matter Mass within 15 kpc must be 6 x 10 11 solar masses Dark halo of dark matter About 15% of the matter in the universe is made of visible matter 85% dark matter...
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- Fall '08