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Introduction to
Astrophysics and Cosmology
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COSMOLOGY
Galactic recession has always carried a moderate public interest, perhaps due to comprehensive difficulties of how the universe can expand.
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Originally discovered by Hubble, whom spent much of the 1920’s measuring and cataloging both the distance and Doppler shifts of galaxies using rather primative instrumentation. What he found was shocking to the scientific community at the time – namely, that all distant galaxies are receeding from us. Moreover, the farther away the galaxy was, the faster it was speeding away from us! Taking the somewhat bold assumption that we are indeed not the center of the universe (as most Americans like to think), Hubble plotted their recession speed v against their distance r. This analysis showed a linear relationship, which, in science, often implies that it is something at a more fundamental level. This relationship came to be known as the Hubble Law, v = H0 r.
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The slope of the line, H0, is known as the Hubble Constant.
Hubble’s observation of this recession, or redshift, demonstrated the Universe itself to be expanding.
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