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# l19p - Today How do we determine distances Announcements No...

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ISP209s8 Lecture 19 -1- Today • Announcements: – No one got a perfect score on Exam #2, so I will make the exam out of 39 – HW#8 is due 26 March at 8:00am. – Watch for the chance to vote on the Spring Break Stories. The size of the Universe The Big Bang ISP209s8 Lecture 19 -2- How do we determine distances? Radar – nearby things like the Sun Parallax – 1 arcsec motion 1 parsec (pc) = 3.24 ly Spectroscopic parallax – use location on the Hertzsrpung Russell diagram ISP209s8 Lecture 19 -3- Stellar Parallax 1 arcsec corresponds to a distance of 1 parsec (pc) = 3.24 ly Distances to 300 ly can be measured this way ISP209s8 Lecture 19 -4- Why is there always r 2 ? I hate r 2 . 2 d 4 L[Watts] intensity π = Inverse square law If we know L the luminosity (measured in watts), and measure the intensity, we can determine d, the distance to the source

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ISP209s8 Lecture 19 -5- Hertzsprung-Russell Diagram ISP209s8 Lecture 19 -6- Map of the night time sky ISP209s8 Lecture 19 -7- The Great Galaxy in Andromeda – M31 ISP209s8 Lecture 19 -8- The Pace of Science Astronomers have studied the sky for thousands of years, but 90% of all astronomical information has been obtained obtained since 1900. For example, in 1900 scientists believed that the universe: Was infinitely old Was infinitely large Contained only one galaxy (the Milky Way) Did not change with time Was uniform throughout (problem with Olber’s paradox) All of these are false!
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l19p - Today How do we determine distances Announcements No...

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