Help for Part II of the GalaxyZoo.org Project: Galaxy Properties
The data table mentioned in Part II, number 1 of the GalaxyZoo.Org Project writeup in the Student Course Activity Guide is available as an Excel spreadsheet or a PDF document you can print.
Correction for Observing Project Writeup:
For question 6 of Part III, the question should read:
Explore object ID 587731520668631247. Classify this object as either elliptical or spiral and give a short explanation (a couple sentences long) describing why you made the choice you did. Your choice should address shape, color, and spectrum.
Step-by-step instructions for finding the the numbers u and r and the spectrum:
- Download the Excel spreadsheet or
a PDF document version of the data
table for recording the data.
- Log in, go to Galaxy Analysis, then click on "Show My Galaxies".
A list of all of your galaxies comes up, and one column is the "Galaxy
Ref" number. See the pic below.
- To see an individual galaxy, click on its Galaxy Ref number.
- Click on the number below the picture and a new window will open
up with more info about that galaxy.
- When the screen with detailed info comes
up, check to see if you can use the galaxy...it needs to have a spectrum.
You can see a picture of the screen for
- The numbers u and r that you want are shown below. See the sidebar on "About u,r, and color" for details.
About u, r and color
The numbers u and r are called magnitudes. The amount of blue light from the galaxy is related to u and the amount of red light is related to r. The magnitude scale is backward so a big number means less light. For examply, if one galaxy has u=17 and another has u=14, the galaxy with the smaller u, 14 in this case, is the one that emits more blue light.
The difference u-r tells you about the amount of red light compared to blue. Larger u-r means a redder color and smaller u-r means a bluer color.
- The color is the difference u-r. For the sample just above, that is 16.29-14.28,
which is 2.01. See the sidebar on "About u,r, and color" for details.
- The
spectrum is the graph that appears on the detail page.
See the good
galaxy picture (below) if you aren't sure what spectrum is.
(click on image for larger view of image)
