The spectra of stars and galaxies

The spectra of stars and galaxies can both show shifts from their expected wavelengths, but for different reasons. The spectra of stars shift due to the Doppler effect--so because of motion--and they can shift blue (to shorter wavelengths) or red. Galaxies on the other hand almost always shift to the red, so in general we refer to these shifts as redshifts. In this lab you will investigate the redshifts of stars and galaxies. The redshift* has already been calculated for all SDSS spectra, you can find it under Explore, or printed in the header of every SDSS spectrum, like this: z=0.024. Although you don't have to calculate the redshift for your objects, I'll ask you to calculate the velocity required for the Doppler effect to produce the observed redshift. Fortunately that's easy: v = cz where v is the velocity, c is the speed of light (lets all use c=3.00*105 km/s) and z is the redshift. You'll investigate redshift by collecting some stars and galaxies that have spectra. 1. Navigate to Voyages: Red shift (Links to an external site.)Links to an external site.. 2. Since you completed My Special Place in the SDSS, click the "I Have a Starting Place" button. 3. Follow the instructions there to load a list of spectra from your location. 4. Re-open Voyages: Red shift (Links to an external site.)Links to an external site. and follow the instructions there to load a collection of stars. In addition to their instructions, write "=0" in the warning column to cut out spectra with bad red shifts (usually very dim stars). 5. Click anywhere in the rows for the lowest and highest red shift stars to open their Spectrum Detail pages. These pages have the star's spectra, thumbnail images and other information. Thumbnail image of a distant object Copy the thumbnail images for these two stars to your document, and label with their red shifts, rounded to a few significant figures. 6. Change the class to galaxy (type GALAXY in the class box) without changing the other columns. Open the Spectrum Detail pages for the lowest and highest red shift galaxies left in your table. If the table is blank, I'm sorry, but you should go back and find a new place by clicking the "Use Constellations Notebook" button in step 2. 7. Now create a page that shows: o Thumbnail images of the lowest and highest red shift stars from your sample, labelled with their red shift and velocity (use the red shift equation, v = cz, as explained above). o Thumbnail images of the lowest and highest red shift galaxies from your sample, labelled with their red shift. o Then write a short paragraph answering the following questions:  What is the average red shift for the stars you found, and for the galaxies? How do the stellar red shifts compare to the galactic red shifts?  For the galaxy with the greatest red shift, are its spectral lines shifted to longer or shorter wavelengths?  For this galaxy, calculate the velocity that corresponds to it's red shift.  Is this galaxy moving toward or away from us? You're welcome to use PowerPoint, Word, Keynote, or any tool that can arrange pictures and text on a page, but please submit either a Word document or a PDF. * Red shift is defined as if it is a Doppler shift: the shift in wavelength is the observed wavelength subtracted from the resting (non-moving) wavelength, divided by the rest wavelength:                                                                                                                                            

Sample Solution