# Physics 103 fall 2001 Laboratory Exercise #6 – Part I galaxy classification purpose

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Group Name ________________________________ Section ______________________
Lab Partners: Date _____________________
PHYSICS 103

FALL 2001

Laboratory Exercise #6 – Part I

## GALAXY CLASSIFICATION

Purpose: To develop a system by which to classify galaxies. To experience why classification is an important first step to understanding. To experience the difficulty with any classification scheme.

## INTRODUCTION

When faced with a new kind of object, the first thing scientists usually do is describe what it looks like. Then they identify features that appear the same as or different from other members of the new class. Finally, they try to understand what causes these similarities and differences.

This activity encourages you to look at photographs of galaxies and to discover similarities and differences in the way they look. You will then sort the galaxies into different categories, based on what you see. Astronomer Edwin Hubble did essentially the same thing in the 1920s, when he devised a system for classifying galaxies by shape that proved extremely useful in helping us understand galaxies. His system is still widely in use, although it is being modified by new discoveries that indicate that galaxy shape depends greatly on the environment in which a galaxy is born.

## PART 1: DEVISE A CLASSIFICATION

### Instructions

On the following pages you will find images of 32 different galaxies. You will devise a scheme by which to classify the galaxies. First, look at all the galaxies. Ask yourself and your lab partners: What types of features do these galaxies possess? What are some similarities and differences between the different galaxies? Try to put the galaxies into classes or categories. YOU MAY SEPARATE THE IMAGES IF IT WILL HELP. Once you have placed the galaxies into categories, come up with names and descriptions of each category.

 1) M31 2) M32 3) M49 4) M51

 5) M59 6) M61 7) M64 8) M81

 9) M82 10) M83 11) M84 12) M86

 13) M87 14) M88 15) M89 16) M101

 17) M104 18) M109 19) M110 20) Arp 252

 21) LMC 22) Leo I 23) NGC 253 24) NGC 1302

 25) NGC 1365 26) NGC 2146 27) NGC 3351 28) NGC 4565

 29) NGC 4596 30) NGC 5383 31) NGC 6946 32) NGC 7743

On this page, describe your classification system. Be sure to give the name of each class and describe the properties each class does or does not posses. Be specific. If I give you another galaxy, you should be able to place it into a category based on these descriptions.

In the table below write the class each galaxy belongs to.

 Galaxy Class Galaxy Class 1) M31 17) M104 2) M32 18) M109 3) M49 19) M110 4) M51 20) Arp 252 5) M59 21) LMC 6) M61 22) Leo I 7) M64 23) NGC 253 8) M81 24) NGC 1302 9) M82 25) NGC 1365 10) M83 26) NGC 2146 11) M84 27) NGC 3351 12) M86 28) NGC 4565 13) M87 29) NGC 4596 14) M88 30) NGC 5283 15) M89 31) NGC 6946 16) M101 32) NGC 7743

When you reach this point, ask the instructor for Part 2 of the lab.

PART 2: CLASSIFY GALAXIES IN YOUR SCHEME
Below are images of two more galaxies. Next to each, write the name of the class in your scheme to which you would assign each galaxy.

NGC 1201

The Milky Way – Artist’s conception
When you reach this point, tell the instructor you are done and wait for Part 3.

PART 3: HUBBLE’S CLASSIFICATION SYSTEM

Astronomers have been using a classification scheme developed by Edwin Hubble in the 1920s. Read about this system in your textbook, chapter 15 pages 378-383. In the space below, write a brief description of each class of galaxy. Note: While the descriptions in the book are correct, some of the classifications given for specific galaxies are slightly off.

In the table below write the Hubble class each galaxy belongs to.

 Galaxy Class Galaxy Class 1) M31 17) M104 2) M32 18) M109 3) M49 19) M110 4) M51 20) Arp 252 5) M59 21) LMC 6) M61 22) Leo I 7) M64 23) NGC 253 8) M81 24) NGC 1302 9) M82 25) NGC 1365 10) M83 26) NGC 2146 11) M84 27) NGC 3351 12) M86 28) NGC 4565 13) M87 29) NGC 4596 14) M88 30) NGC 5283 15) M89 31) NGC 6946 16) M101 32) NGC 7743 NGC 1201 Milky Way

You have finally reached the end of the lab.

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