Name(s): ______

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Date: ______Course/Section: ______

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Astronomical Redshift

Part 1: Measuring Rest Wavelengths

1. Calculate the wavelengths of the Balmer series for Hydrogen in Angstrom (Å).

Balmer Line λ Hα

Hβ

Hγ

Hδ

Hε

2. Sketch the spectra of Hydrogen, label the axes, and the peak lines by both their wavelength and Balmer name.

Part 2: Measuring Redshifted Wavelengths

1. Identify the emission lines in the spectrum of a quasar and record their measured wavelengths in the table below. Use the graph in Part 2 of the lab website to help identify the lines. Then, compute the redshift.

Rest Wavelength Peak Wavelength Emission Line Redshift λrest λpeak

2. Examine your calculated redshift values. Which values seem suspect to you? Explain why you would discard those measurements. Then, determine which values you believe and then determine a characteristic redshift of the galaxy.

3. Why can you assume a characteristic redshift?

4. Calculate the velocity of the galaxy in km/s.

5. Using the distances given in the .PDF, make a plot of velocity in km/s vs distance in Mpc for all the galaxies. You can make this plot in Logger Pro, Excel, or python. Fit a line to your data to find the slope of the line. What is this value and what, conceptually, does it mean? Explain how this value and your plot describe the universe.

6. With your value of the Hubble constant, calculate the age of the universe.

7. Compare your results with the known Hubble constant, 71 km/s/Mpc, and the age of the universe.

8. Quantify your errors, meaning write a small summary about how you would do this lab differently, given what you now know.