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# astlahp - Laboratory 9 Calculation of the Age of the...

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60 Laboratory 9 - Calculation of the Age of the Universe Materials Used: Spectral photos, vernier calipers, Excel spreadsheet. Objectives: To study redshifts and recession velocity; to determine the Hubble Parameter; to determine the age of the Universe with a Hubble Plot. Discussion: In the late 1920's astronomer Edwin Hubble discovered that galaxies were receding, i.e., from a reference frame in any galaxy all distant galaxies are moving away. A decade later Hubble and M. L. Humanson demonstrated that the more distant a galaxy the faster it is moving away with the discovery that distant galaxies have spectral lines that are strongly shifted toward the red (longer wavelength) end of the spectrum. This shifting of spectral lines is referred to as the l a w o f r e d s h i f t s . Hubble produced a plot of the recession velocity of galaxies vs. their distance from the Milky Way. This plot, known as a H u b b l e P l o t , revealed that the more distant a galaxy the higher its r e c e s s i o n v e l o c i t y and that the increase in recession velocity is directly proportional to distance. This was the evidence needed to herald the end of the S t e a d y S t a t e theory of the Universe and usher in the concept of an expanding Universe that began with the Big Bang. In this procedure you will determine the Hubble Parameter, H o , which is used to estimate the rate of expansion of the Universe, and produce a Hubble Plot to estimate the age of the universe. Many careful measurements and numerous calculations are required to determine the Hubble parameter and produce a Hubble plot. In this procedure you will take measurements and perform calculations just like any astronomer would to make the same determinations. A spreadsheet, Hubble_Plot.xls, has been created to aid you with the calculations required. Accurate measurements are crucial in obtaining a good value for the Hubble Parameter and a reasonable estimate for the age of the Universe. Take your time with each measurement and be as meticulous as you can. Procedure Calibrating the Spectrometer Figure 1 contains images of five galaxies on the left with spectral data for each galaxy (and reference spectra above and below) on the right. The images of all five galaxies were acquired at the same magnification so the smaller the image of the galaxy the farther away it is. The galaxies are similar in shape and for this exercise we will assume that they all have a diameter of about 100,000 light years. The spectra of all five galaxies were obtained with the same diffraction grating. The reference spectra are included in order to calibrate the grating, which is accomplished by determining its d i s p e r s i o n . The reference spectral lines are labeled a through g , and their corresponding wavelengths (in angstroms) are: a - 3889Å b - 3965Å c - 4026Å d - 4144Å e - 4472Å f - 4713Å g - 5016 Å You will begin by measuring the distance between the “a” spectral line and all of the others.

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