Astronomy 201: Cosmology

Fall 2009

Prof. Bechtold

The Galaxy Zoo Project

200 points

Due: Nov. 24, 2009 in class

Professional astronomers often have to search through enormous quantities of data in order to find an interesting result. Usually, the approach is to write a computer program to search the data automatically. But there are some types of analyses that are difficult to train a computer to do. Human brains are very good at seeing patterns in complex images, and it turns out that it’s sometimes hard to write a computer program to do as good a job at pattern recognition as a human. For example, in medical imaging, it is now standard to use digital cameras to take mammograms and to do other types of cancer screening, and computer programs are used to flag suspicious structures in the images, but in the end, the images are looked at by a pathologist, because there is no substitute for a “trained eye.”

In this homework, you are going to participate in an interesting on-line project which uses “the public” to classify galaxies as spirals, ellipticals, etc.. This project is called “The Galaxy Zoo.”

The Galaxy Zoo is based on images taken with the Sloan Digital Sky Survey telescope in New Mexico. This telescope has taken millions of images and millions of spectra of stars, galaxies and quasars. The data is all on-line, and professional astronomers have been “data mining” the Sloan Survey for several years. They have found all sorts of interesting results.

The Galaxy Zoo project is basically interested in producing a catalog of the “galaxy type” for millions of galaxies in the Sloan Digital Sky Survey. It trains you to classify galaxies in terms a few simple rules, gives you some example galaxies to classify, and then lets you classify as many galaxies as you want. Your classifications are added to the millions that have already been done by others. Each galaxy is classified by many different people, so if you enter something “wrong” they will be able to flag your classification as suspect – i.e. if you say some galaxy is a spiral and a hundred other people say its an elliptical, they will throw your classification out.

So there is no real right or wrong answer. The point of this homework assignment is to familiarize you with a “citizen astronomy” project, and let you look at a number of real galaxies. In classes and textbooks, we tend to show pictures of beautiful galaxies, but real galaxies are a lot messier. And you can tell your friends and family that you got to do real astronomical research as part of this class! By completing this assignment, you will be contributing to a state-of-the-art astronomical research project.

The first “citizen astronomy” project was “SETI at Home” which is still going on. This is a project where you download a program to your computer and analyze radio signals from radio telescopes to look for communications from extra-terrestrial civilizations. See their web page: http://setiathome.berkeley.edu.

Another “citizen astronomy” project is “Stardust at home” where you help astronomers look for interplanetary dust grains on aerogels from the Stardust project. See http://stardustathome.ssl.berkeley.edu/

Here’s what do do for this homework assignment.

1. Register as a Galaxy Zoo User. Go to

http://galaxyzoo.org/

This is actually “Galaxy Zoo 2” – the second project to collect galaxy classifications.

Click on “Register” underneath “Classifier Log In” (see below).

For your “User Name” and “Display Name” please give your firstname_lastname. So for example, if your name is “Edwin Hubble” your user and display name should be Edwin_Hubble. Once you have registered and logged in, your results can be saved.

2. Read the instructions, and do the practice exercises. Click on “The Story So Far”, “The Science” and “How to Take Part”. The page called “How to Take Part” walks you through how to classify galaxies. Do their examples and figure out what they are looking for.

3. Classify Galaxies. Click on Classify Galaxies, and a galaxy will pop up for you to classify. Answer the questions indicated. Classify at least 50 galaxies. You do not have to do them at one sitting – if you are logged on when you are classifying galaxies, it will keep your classifications for you to look at later on.

4. Print out “My Galaxies”. When you click on “My Galaxies” you get a page which shows you the galaxies you have classified. When I did this the other day I got:

You can click on the thumbnails of the galaxies and see more information about the galaxies you classified.

When you have classified 50 galaxies or more, print out your “My Galaxies” page and turn it in. On my printer it comes out with black text on white background.