Redshift

Description

In this lab, students compare typical redshifts of stars and galaxies in the SDSS using SkyServer and Voyages.

Procedure

In this lab, you will investigate the redshifts of stars and galaxies.Your book describes redshift in several places, but for your reference it is defined as:

z = (λobserved -λrest) / λrest

This quantity is called redshift, and has already been found for all SDSS spectra. Although you don't have to calculate the redshift for your objects, I will ask you to calculate the velocity that would produce the observed redshift by the Doppler effect . To do this, use:

cz = v

where c is the speed of light (lets all use c=3.00*105 km/s), z is the redshift, and v is the velocity. You'll investigate redshift by collecting some stars and galaxies that have spectra.

    1. Navigate to Voyages: Redshift.

    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. Return to Voyages: Redshift and follow the instructions there to load a collection of stars in redshift order. In addition to their instructions, write "=0" in the zwarning column to cut out spectra with bad redshifts (usually very dim stars).

    5. Click anywhere in the rows for the lowest and highest redshift stars to open their Spectrum Detail pages. These pages have the star's spectra, thumbnail images and other information.

    1. Thumbnail image of a distant object

    2. Copy the thumbnail images for these two stars to your document and label them with their redshift-- rounded to a few significant figures--and velocity (use the redshift equation, v = cz, as explained above).

    3. Now change the class to galaxy (type GALAXY in the class box) without changing the other columns. Copy thumbnail images and rounded redshifts for the lowest and highest redshift galaxies into your document. 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.

    4. Now create a page that includes:

        • The thumbnail images of the lowest and highest redshift stars from your sample, labelled with their redshift and velocity (use the redshift equation, v = cz, as explained above).

        • The thumbnail images of the lowest and highest redshift galaxies from your sample, labelled with their redshift.

        • A short paragraph answering the following questions:

            • What is the average redshift for the two stars you found, and for the two galaxies? How do the stellar redshifts compare to the galactic redshifts?

            • For the galaxy with the greatest redshift, are its spectral lines shifted to longer or shorter wavelengths?

            • For this galaxy, calculate the velocity that corresponds to it's redshift.

            • Is this galaxy appear to be moving toward or away from us?

You're welcome to use any tool that can arrange text on a page, but please submit something Canvas can open (Microsoft Word, Powerpoint, or a pdf).

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