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UCCS PES 1060: Astronomy II Chapter 18 Problems Worksheet name: __________________________ 1. A beam of light shining through a dense molecular cloud is diminished in intensity by a factor of: 2 for every: 5 pc it travels. By how many magnitudes is the light from a background star dimmed if the total thickness of the cloud is: 60 pc? 60 5 It gets reduced by: 2 a total of: = times as it passes through the cloud. Thus, the light is dimmed by a factor of: it entered the cloud. 212 4096 . times fainter than it was before This corresponds to: 9 magnitudes, since 2.512 4000 . 9 The number of magnitudes can be directly calculated using the formula: 2.5 Log ( 4096 ) = 2. A star of apparent magnitude: 10 lies at: 500 pc from Earth. Interstellar absorption results in an average extinction of: 2 magnitudes per kilo parsec. The apparent magnitude of the star is being made dimmer by the presence of dust. Over half a kiloparsec (500 pc), this extinction will be only: 1 magnitude. Without the effects of dust, the apparent magnitude would be: +9. a. Find the absolute magnitude (M): ( apparent magnitude without dust ) - { 5 log10 [ ( distance from Earth ) / ( apparent magnitude with dust ) ] } / [ log10 ( (5)( minus )] = ) = = Abs Mag b. Find the luminosity L, (in solar units) of the star with an absolute magnitude M = 0.51. L (solar units) = 10 – ( M L (solar units) = 10 – ( 0.51 L (solar units) = 10 – ( ) / 2.5 L (solar units) = 10 – ( ) L (solar units) = 10 ( ) L (solar units) = - 4.83 ) / 2.5 - 4.83 ) / 2.5