Lecture15 - Signature Course UGS 303 (Fall 2009) Big Q:...

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1 The History and Philosophy of Astronomy (Lecture 15: Birth of Astrophysics) Instructor: Volker Bromm The University of Texas at Austin Department of Astronomy Signature Course UGS 303 (Fall 2009) Big Q: What is the Nature of the Stars? Which questions would an astronomer have asked about the stars in the early 1800s? • How far away are they (stellar distance scale)? • What are the stars made of (stellar composition)? • How long do they live (stellar lifetimes)? • By what mechanism do they shine? • Is the Sun just a (nearby) star? A: Yes, already widely believed (Descartes, Newton) • How massive are they? Can we ever know the `Physics of the Stars ʼ ? • Auguste Comte (1798-1857) • founder of `Positivism ʼ - real knowledge only due to hard facts, e.g., laboratory science, measurements • claimed that we will never know the nature of the stars - distant stars are forever out of our reach - we cannot conduct laboratory experiments with them (= astrophysics)
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2 The Hunt for Stellar Parallax! The Hunt for Stellar Parallax! Resolution Measuring the Distance to the Stars • Friedrich Wilhelm Bessel (1784-1864) • highly talented in astronomy and mathematics (“Bessel functions”) • director of Konigsberg Observatory • 1838: First stellar parallax . . Q: How to select promising candidates? • possible criteria: 1) brightest stars 2) most rapid proper motion Bessel ʼ s choice! • need to train your telescope on nearby star!
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3 Stellar Motions on the Sky • proper motion 1/d d Q: How to select promising candidates? • 61 Cygni: the `fying star ʼ (5 arcsec per year) Great Success: First Stellar Parallax (1838)! Bessel
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This note was uploaded on 12/18/2010 for the course UGS 303 taught by Professor Foster during the Spring '08 term at University of Texas at Austin.

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Lecture15 - Signature Course UGS 303 (Fall 2009) Big Q:...

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