Describe the experiment that Edwin Hubble conducted, which led to Hubble\'s Law.

Question

Describe the experiment that Edwin Hubble conducted, which led to Hubble's Law. Why might this have led to the wrong value for Hubble's constant? How could one carry out a more precise experiment nowadays? The term red shift is widely used in astronomy. Distinguish the two different types of redshift in astronomy and cosmology, explaining what they correspond to. Using very deep multi-wavelength imaging data from the Hubble Space Telescope, astronomers have recently discovered a number of galaxies which could lie at very large distances using the Lyman-break technique. What is the Lyman-break technique? A group in France recently targeted some of these galaxies using the Very Large Telescope in Chile. They found an emission line from one of the galaxies with a wavelength of = 1.1673 mu/m. Assuming this emission line is the Lyman-alpha line of Hydrogen, with a rest-frame wavelength of lambda rf = 1216A. determine the redshift of this object. The result of (d) indicates this galaxy resides in what is known as the epoch of reionization. Describe what is meant by the term "the epoch of reionization".

Explanation / Answer

Hubble, aided by Milton Humason extended the work of Slipher by using the larger Hooker telescope. He took long exposures of the spectra of faint galaxies.
By measuring the amount of shift of specific spectral lines relative to those produced by reference arc lamps in the spectrograph he was able to calculate values for the galaxy velocities. This proportionality between distance and speed of galaxies was formulated in 1929 by Hubble and Humason, and is known as Hubble's Law. It was an extraordinary discovery; one that meant that the universe was constantly expanding The mathematical equation for Hubble's law is as follows:
                                      v = H0D Hubble constant at the time of observation in the history of the universe. (A megaparsec is 3.26 million light-years.)

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