1. The Universe Looking at Galaxies

2. The Universe Early in the history of the universe, hydrogen and helium (and other forms of matter) clumped together by gravitational attraction to form countless trillions of stars. Billions of galaxies, each a cluster of billions of stars, now form most of the visible mass in the universe.

3. When stars are viewed through a telescope, they appear as points of light. However some objects in the sky look like "fuzzy" clouds. Some are nebulae (star-forming regions) Others are actually islands of stars that are much farther from us than the individual stars we see in the night sky. These islands are galaxies.

4. © 2011 Pearson Education, Inc. Hubble’s Galaxy Classification This pair of images shows the Coma cluster of galaxies. Almost every object visible is a galaxy.

5. Galaxies Galaxies are systems of stars, gas and dust They exist in a wide variety of shapes and sizes 4 basic types

6. Galactic Inquiry Purpose: Recognize that galaxies are a collection of stars Understand that galaxies take a variety of forms Learn to develop your own classification scheme to understand how scientists classify Comprehend the four major categories of galaxies

7. Galactic Inquiry 1.Looking at the 15 pictures of galaxies develop your own classification system 2.Get a Hubble classification system from me and use the Hubble tuning fork to reclassify the galaxies 3.Answer the reflection questions.

8. Review Four basic types elliptical, spiral, barred spiral, and irregular

9. Elliptical Galaxies About 60% of the galaxies are round to oval in shape

10. © 2011 Pearson Education, Inc. Elliptical galaxies have no spiral arms and no disk. They come in many sizes, from giant ellipticals of trillions of stars, down to dwarf ellipticals of less than a million stars. Ellipticals also contain very little, if any, cool gas and dust, and they show no evidence of ongoing star formation. Elipticals have large clouds of hot gas, extending far beyond the visible boundaries of the galaxy. Hubble’s Galaxy Classification

11. © 2011 Pearson Education, Inc. Ellipticals are classified according to their shape from E0 (almost spherical) to E7 (the most elongated) Hubble’s Galaxy Classification

12. © 2011 Pearson Education, Inc. What would you classify this galaxy? Tell your elbow partner why.

13. Spiral galaxies Have a central nucleus surrounded by a flattened disc with the stars, gas, and dust organized into a pattern of spiral arms. Greater concentration of stars near their centers

14. Spiral galaxies are classified according to the size of their central bulge Hubble’s Galaxy Classification

15. © 2011 Pearson Education, Inc. Type Sa has the largest central bulge, Type Sb is smaller, and Type Sc is the smallest. Type Sa tends to have the most tightly bound spiral arms with Types Sb and Sc progressively less tight, although the correlation is not perfect. Hubble’s Galaxy Classification

16. © 2011 Pearson Education, Inc. Hubble’s Galaxy Classification The Sombrero galaxy, with its large central bulge, is a type Sa. We cannot see the spiral arms, as they are edge-on.

17. Turn to your elbow partner  One of you hold up a text book or notebook for your partner with the edge facing your partner.  Now hold the book with the title facing your partner. How does the book look different. Which is more recognizable as a book?  Try this with a pen. Look down the top of the pen. Now look at it from the side. How is the image different?

18. © 2011 Pearson Education, Inc. Similar to the spiral galaxies are the barred spirals Hubble’s Galaxy Classification

19. Barred Spiral Has a bar through the center with arms extending through the bar The variation from SBa to SBc is similar to that for the spirals

20. What is this classified as?

21. Irregular Galaxy These galaxies have little symmetry in their structure About 10% of the galaxies

22. © 2011 Pearson Education, Inc. The irregular galaxies have a wide variety of shapes. The small and large Magellanic Clouds are close neighbors to our own Milky Way. Hubble’s Galaxy Classification

23. © 2011 Pearson Education, Inc. Here are several other irregular galaxies: AM 0644-741 and its neighbors on the left, and NGC 1569 on the right. Hubble’s Galaxy Classification

24. © 2011 Pearson Education, Inc. Hubble’s “tuning fork” is a convenient way to remember the galaxy classifications. Hubble’s Galaxy Classification

25. © 2011 Pearson Education, Inc. Let’s locate a few galaxies on Stellarium M31 in Andromeda a spiral galaxy M81 in Ursa Major a spiral galaxy M95 in Leo a barred spiral M87 in Virgo (near Mars) an elliptical