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Discovery of the Expansion of the Universe

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Shapley's View of the Universe
Harlow Shapley's main arguments were: (1) Our Galaxy was very large, approximately 300,000 light years in diameter. This measurement was quite drastic, compared to the previous measurement made. (2) Sun was not at the center of the galaxy, it was approximately 60,000 light years away. This is because the globular clusters were observed to be concentrated towards one half of the sky. Also, the distances of the variable stars implied that the globular clusters were far away. (3) He believed that Milky Way was so large that it was the entire Galaxy (4) Spiral Nebulae were just gaseous clouds located within our Milky Way. He modeled this by observing the globular star clusters. (Zabludoff, 2012) Previously, the distance to one of the prominent globular cluster called M13 was determined by an astronomer and from this he assumed that all the globular clusters were nearly the same size. To derive the distance to the star, Shapley used the Cepheids. He measured the period over which Cephied variable star fluctuates. This period is related to its intrinsic brightness. From measuring the period, he determined its intrinsic brightness/ luminosity and then compared the intrinsic brightness to the observed brightness to determined the actual distance of the stars. He found that the cluster formed a halo around the flat, disk-shaped body of the rest of the galaxy. He concluded that the nebulae did not lay beyond the Milky Way. His theory was that the nebulae was just part of the solar system still in the process of formation. (GEAS,2006) Adriaan Van Manen, was one of Shapley's colleagues at the Observatory he worked. He took photographs of the spiral nebulae and by comparing the photographs of the nebulae over ...

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... Universe expand forever?” http://wmap.gsfc.nasa.gov/universe/uni_shape.html The Sloan Digital Sky Survey (SDSS) “The Expanding Universe” http://skyserver.sdss.org/dr1/en/astro/universe/universe.asp The General Education Astronomy Source (GEAS) (2006) “The Shapley-Curtis Debate – What is our Place in the Universe?” New Mexico State University http://astronomy.nmsu.edu/geas/lectures/lecture27/slide01.html Zabludoff .(2012) “A Great Debate: Shapley vs. Curtis and the Scale of the Universe (1920)”. The University of Arizona http://atropos.as.arizona.edu/aiz/teaching/a250/shapley_curtis.html Cary Sneider, “1929: Edwin Hubble Discovers the Universe is Expanding”, Carnegie Institute for Science http://cosmology.carnegiescience.edu/timeline/1929 Swara Ravindranath, "Edwin Powell Hubble", March 2009, pp. 211-213
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