PPT-Distances of the Stars

Key Ideas Distance is the most important amp most difficult quantity to measure in Astronomy Method of Trigonometric Parallaxes Direct geometric method of finding distances Units of Cosmic Distance. Galaxies . And the Foundation of Modern Cosmology. How are the lives of galaxies connected with the history of the universe?. Hubble Deep Field. Our deepest images of the universe show a great variety of galaxies, some of them billions of light-years away. Introduction. Trigonometric Parallax . Spectroscopic Parallax . Cepheid Variables . Type Ia Supernovae. Tully-Fisher Relationship. Hubble’s ‘Law’ . Trigonometric Parallax. While fundamental, this method is very limited in terms of how far away one can use it. For large numbers of star, ground-based measurements of parallax do not get beyond about 20 pc, although on individual objects this can be extended to about 100 pc (with much effort). . 23. vs. .. 1. First spiral nebula found in 1845 by the Earl of . Rosse. . Speculated it was beyond our Galaxy.. 1920 - "Great Debate" between Shapley and Curtis on whether spiral nebulae were galaxies beyond our own. Settled in 1924 when Edwin . ’ Stars . . Supremely Important. In order to make the most important astrophysical determinations, including. True (intrinsic) brightness. , . mass, . size, . e. tc. …. we . have to . know the distances.. Universe. Imagine that you find a star with an unknown distance, but you notice that it has a distinctive characteristic that tells you that it is a specific type of star. And let’s imagine that all stars of that type have the same luminosity, and you happen to know the value of that luminosity. You can then estimate the distance for the star you found from the inverse square law of light:. What is a Constellation?. A specific group of stars.. Ancient people of many cultures . connected. groups of stars to form patterns, like huge dot-to-dot puzzles.. These . patterns. are known as constellations. . Spiral Nebulae: . A Huge Challenge!. The . ‘. Great Debate. ’. Curtis . vs. Shapley (. 1920). : . are the nebulae big, . even comparable . to our own Milky Way (as Curtis argued)?. or are they small satellites of the Milky Way (as Shapley maintained). Distances:. The Principle. . ‘. Real Life. ’. Distance . Determinations . We . use various . ways; . y. ou can think . of . several! For instance, you notice that a car down the road ‘looks small’,. Islands of Stars. Our goals for learning. :. How are the lives of galaxies connected with the history of the universe?. What are the three major types of galaxies?. How are galaxies grouped together?. .. 1. First spiral nebula found in 1845 by the Earl of . Rosse. . Speculated it was beyond our Galaxy.. 1920 - "Great Debate" between Shapley and Curtis on whether spiral nebulae were galaxies beyond our own. Settled in 1924 when Edwin . An . Astronomical Unit . (AU) is defined as the average distance between the Earth and Sun. . . 1 AU = . 92 955 807 miles . or . 149 597 871 km. AU’s are used to measure distances within the solar system. . The “. Cosmic Distance Ladder. ”. Visual. “. Parallax. ”. “. Binocular. Vision”…. Let’s us “see” 3D images . (depth). …but, how to do this to get . Astronomical Distances. ?. “. What is a Constellation?. A specific group of stars.. Ancient people of many cultures . connected. groups of stars to form patterns, like huge dot-to-dot puzzles.. These . patterns. are known as constellations. . R. Ellis & S. G. Djorgovski. Winter 2011. Class Logistics. All info, lecture notes, useful links, . homeworks. , exams, announcements, etc., will be on the class website:. http://www.astro.caltech.edu/~schenker/ay124.