Themes > Science > Astronomy > Modern Astronomy > Cosmology > Expansion of the Universe > The Hubble Law

Here you will have an opportunity to measure redshifts for several galaxies using a set of common spectral lines here. While the spectra that you will be using have many lines (emission and absorption) concentrate on using the following sets:

Calcium H and K

These are very prominent absorption lines is most all galaxies. An example is shown here:

These pair of absorption lines will appear in all the spectra and they should be your principle source for determining the redshift.

Hydrogen Emission Lines

In addition, some galaxies have emission lines that are principally due to hydrogren recombination. One of these lines that appears in these spectra is H-beta which is shown below:

Note that not all the galaxies have this line but in those cases where its present, it should be measured in addition to the Calcium H and K lines.

Exercises:

1. Measure redshifts and angular diameters for the 28 galaxies that are in the applet. To measure the angular diameter, center the galaxy image in the available reticle and meausure its angular diameter in units of recticle rings. Note that the box which sees diameter is not functional - please dont' type in it. In your lab book write down the angular diameter of the galaxy, the observed wavelengths of the 3 lines you have measured in the spectra, and any notes about the appearance of the galaxy (e.g. spiral, elliptical, etc). Also note if the galaxy spectra has emission lines in it or not.

2. Now determine the redshift of each galaxy and make a plot of angular size vs redshift. What does this plot tell you?

3. Also determine if there is a correlation between the presence of emission lines in the spectra and the overall appearance (morphology) of the galaxy.

Information supplied by: http://csep10.phys.utk.edu