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©2011 John Sohl, Department of Physics, Weber State University, Ogden, UT 84408-2508 - page 6 / 7





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Now that we know how far away the subject galaxy is, we need to determine the recessional velocity using equation (2). Using the data from column 3 for the K line we get

This result is inserted into column 7 and these steps are repeated for the H line (when it is not “off scale”) with the result going into column 8. The values in columns 7 and 8 are then averaged and then that average is entered into column 9. (If you only have data for the K line then just enter column 7's data into the spot in column 9.)

We have now determined how far away the galaxy is and how fast it is moving, next we use equation (3) to determine how long it took for the galaxy to get to that position. Using our values from columns 6 and 9 we get

This goes into column 10 which is then divided by 3.15 X 107 seconds per year (s/yr) to obtain the value (in years) that is shown in column 11 (1.27×1010 years).

The final step is to average all of your values in column 11 (you might as well use my values as part of your average too). This goes at the bottom of column 11 and is your best estimate of the age of the universe. So that you can work yourself though another example, if you need to, I have included on the worksheet the data and analysis for a second galaxy, Coma 3. Needless to say, you must choose different galaxies in these two galaxy fields (Ursa Major II and Coma Berenices).

NB: Use scientific notation for numbers larger than 99,999 and smaller than 0.0001. Be reasonable with your number of significant figures, use the two examples as a guide.

Final note: The numbers in the last column should be fairly similar for all the galaxies. If it is way off for one of the objects, you probably measured a star and not a galaxy. Try that field again.


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