Science Lab - $20

The Galaxy Zoo

Description:

Astronomy has not yet revealed much about the nature of galaxies. For the most part, astronomers know that they are composed of stars, gas and dust. They appear to have different star formation histories, and differing amounts of the aforementioned constituents, but little is known about how galaxies get to be the way they are.

In order to better understand galaxies, however, astronomers have attempted to divide them into groups by their appearances. It is possible that the appearances of galaxies may be related to their history or evolutionary track. Although, as yet, there is not enough evidence to support this hypothesis, the first step in any endeavor to understand something scientifically, is to classify and compare.

In this exercise, students will look at a number of galaxies and divide them into categories that they determine. Following this, students will compare how their classification scheme compares with the astronomy one.

Introduction:

Galaxies are large groups of gravitationally bound stars, with gas and dust clouds intermingled. In this exercise, you will use the World Wide Telescope to observe several galaxies. You will then divide these galaxies into at least two groups based on their shape and appearance. You will determine the nature of the categories that you develop. At the end of the exercise, you will compare the groupings that you made to those of astronomers and discuss whether grouping galaxies in either way is helpful to understanding the nature of galaxies.

1. Use the World Wide Telescope to observe the galaxies listed in the table at the end of this exercise. Make sure that you look at each galaxy carefully. You can decide how to categorize the galaxies at any point during these observations, but you must designate a category for every galaxy in the table. Your categories can be broad or narrow. You must have at least 2, you should not have more than 10.

[Type answer here – list categories and their abbreviations if any, along with a brief description of each.]

2. Write a description of how you classified the galaxies you observed. What features did you consider in classifying these galaxies? What features did you ignore? Did you develop a symbol or designation for your classifications? What do your symbols or designations mean?

[Type answers here]

3. Now go back and use the Research button for each galaxy to determine the astronomical classification of each galaxy. The designations should be S for spiral, SB for barred spiral, E for elliptical, I for irregular and pec for peculiar. If you are unsure how to interpret the classification for each galaxy, ask for help from your instructor.

[Type answer here]

4. Now compare your classification scheme with the astronomical one. (a) Does either lend any insight into the nature of a galaxy? (b) Is one better than the other?

[Type answers here]

OPTIONAL STEP 5: Read a textbook or other reliable information source to learn more about the morphological classification of galaxies. Write a paper about the insight that has been gained from these designations, if any.

List of Galaxies

NGC 628

NGC 4486

NGC 1300

IC 1623B

NGC 5194

NGC 300

NGC 393

NGC 7331

NGC 3031

NGC 205

NGC 523

NGC 5457

NGC 4472

NGC 1566

NGC 1316

NGC 4594

NGC 221

NGC 536

NGC 620

ESO 286-19

Instructor’s Notes:

It would be best to do this exercise, before discussing galaxy morphology. This will give the students the freedom to choose designations that represent their own way of classifying.

The galaxy morphological classifications of these galaxies can be found using NED and looking for “Basic Data”. In this section, galaxy classification is listed, but classifications will be in designation form, so this will need to be explained to students. The initial information is included in the exercise, but some students will wonder about the numbers following the letter designations. For students who are really getting in to this exercise, there are other, interesting areas to “play” with. Students could be challenged to find an irregular galaxy or a peculiar galaxy that is not interacting, for example.