Modern astronomers have refined Hubble’s classification scheme to include more information about galaxies. However, the modern classification system is still based on the Hubble tuning fork.
Now that you know how to classify galaxies, you are ready to use your knowledge to learn something about what galaxies are like. Below are some ideas for further exploring galaxies in the SDSS data. Choose one, then search through the SDSS data to answer the questions. The Navigation Tool and the SQL Search tool below will help you find galaxies; see the Searching for Data tutorial to learn how to use the SQL Search tool.
Search
Results will appear here
Exercise 5. To prepare for the Research Challenge, make a color-color diagram for a large number of galaxies. Plot u-g on the y-axis and g-r on the x-axis. On your diagram, label each galaxy by its type. Try to identify the areas where different types of galaxies lie on the color-color diagram. Try to come up with rules that will tell you what type of a galaxy you are observing based on its colors. You may want to make other color-color diagrams (such as g-r on the y-axis and r-i on the x-axis) as well.
Research Challenge. The following table contains the redshifts and celestial coordinates of several galaxy clusters. Can you see any differences in the clusters, or the galaxies that make them up, at different redshifts? You may need to make color-color diagrams of several clusters and compare them. Do you notice any differences between rich clusters (with many galaxies) and poor clusters (with few galaxies)?
Click on the Cluster name to launch the Navigation Tool focused on that cluster.
| Cluster | Redshift | RA | Dec |
|---|---|---|---|
Abell 0023 | 0.105 | 5.44 | -0.89 |
Abell 0119 | 0.044 | 14.09 | -1.26 |
Abell 0267 | 0.230 | 28.77 | 1.01 |
Abell 0381 | 0.179 | 41.48 | -0.64 |
Abell 0919 | 0.095 | 151.24 | -0.693 |