tut4

Name: ASTR 311 — Tutorial 4 Galaxy Scales and Classification 1 Galaxy Scales 100,000 lt-yr A A B B C C D D E E Sun Sun The diagram at the left shows an artistic conception of how our galaxy, the Milky Way, would look from outside. The location of the Sun is indicated by a yellow dot. Astronomers use Galactic longitude to indicate how far away from the Galactic centre objects appear on the sky. The radial spokes indicate the Galactic longitude. The circles centered on the Sun show how far away an object is. Each one is 5,000 light-years (or lt- yr for short). The scale is 1 mm is 1,000 light-years. The Galaxy is about 100,000 light-years across. On the diagram are five points in- dicated by the letters A through E. Each of these points is the location of an interesting object; some are the location of several interesting objects. 1. The diameter of the yellow dot is about 1 mm. If you de- picted the size of the Sun on the diagram to scale would it be larger or smaller than the yellow dot? 2. Here is a list of a few of my favourite stars with their distance from Earth in light years. In the third column write the distance in millimeters to place them on the diagram above. In the last column, write which letter corresponds to each object. Several objects may correspond to the same letter. Name Distance (lt-yr) Scaled Distance (mm) Letter Betelgeuse 650 Rigel 860 Arcturus 40 Vega 25 3. Here is a list of a few of my favourite stars with their distance from Earth in light years. In the third column write the distance in millimeters to place them on the diagram above. In the last column, write which letter corresponds to each object. Several objects may correspond to the same letter. Name Distance (lt-yr) Scaled Distance (mm) Letter Crab Nebula 6500 Casseopeia A (radio source) 11000 Omega Centauri (globular cluster) 16000 Sagittarius Dwarf Spheriodal 65000

Now let’s build a scale model of our Galaxy, the Milky Way, in the context of its nearest neighbours, the Local Group of galaxies. Our Local Group contains two large galaxies, the Milky Way and Andromeda. Each are about 100,000 light-years across. The Andromeda Galaxy is about 2,500,000 light-years from the Milky Way. 1. If we represent our Galaxy as a compact disk (12 cm diameter), how far away would be the Andromeda Galaxy? 2. In our Local Group, the next two biggest galaxies are the Large Magellanic Cloud (LMC) and M33. M33 is disk about 50,000 light-years across and the LMC is a bar about 14,000 light-years across. What objects could you use to represent these Galaxies? 3. The LMC is about 200,000 light-years away from the centre of the Milky Way and M33 is about 500,000 light-years away from Andromeda. How far would you place these galaxies from the Milky Way and Andromeda in your scale model? 4. Would you say that galaxies are closer or further apart relative to their sizes than stars are? Why? 5. Would you say that stars or galaxies are more likely to collide with each other than stars? Why? 6. Which happens more often big galaxies colliding with other big galaxies or big galaxies colliding with small ones? 7. The LMC is in the opposite part of the sky to Andromeda, and from the point of view on someone in Andromeda, M33 and the Milky Way are 90 degrees apart on the sky. Draw a diagram showing the four largest galaxies in the Local Group to scale.

In your groups, look at the images of actual galaxies and suggest answers to the following questions. 5. If you had to name the galaxies pictured in the chart based upon their resemblance to common objects, what would you name them? Write your suggestions on the first line underneath each picture. 6. Let’s say that you never heard of the Hubble classification. If you had to classify the galaxies in the chart, how would you do it? Decide on how many groups or classifications you would have and give each group a name. Then, include the criteria you would use to include a galaxy in this group. Group Name Criteria 1. 2. 3. 4. 5. 7. Now classify each galaxy in the chart according to the Hubble scheme. Write the galaxy type and classification below your name of each image on the second line underneath the images (For example, the Andromeda Galaxy is Spiral, Sb.)