- Edwin Hubble developed a classification system for galaxies that included spiral, elliptical, and irregular galaxies. Spiral galaxies have spiral arms and central bulges, elliptical galaxies have spherical or egg-shaped structures, and irregular galaxies have no defined shape. - Galaxies exist in groups and clusters held together by gravity, with galaxy clusters containing dozens to thousands of galaxies. Superclusters are clusters of galaxy clusters and are the largest known structures in the universe. - The Milky Way is part of the Local Group, which also includes the Andromeda Galaxy and other dwarf galaxies. The Magellanic Clouds are two small, nearby galaxies that orbit the Milky Way.

1. Astronomy Topic 06 : Galaxies (part 2) Stephen’s Quintet

3. Hubble Tuning Fork http://www.astro.psu.edu/users/niel/astro1/slideshows/class21/003-hubblefork3.gif

6. M87’s Jet Kitt Peak image Hubble

7. M87-CFH Telescope M87’s jet is visible at the 1:00 position

10. M51-Whirlpool Galaxy (Spiral) http://antwrp.gsfc.nasa.gov/apod/image/0207/m51_hallas_big.jpg

12. M109 http://www.astronomysight.com/as/images/pics/

15. Galaxy Comparisons http://www.glyphweb.com/esky/_images/diagrams/galaxies.gif Elliptical galaxies, such as M87, are the largest known galaxies

18. Galaxy Summary Table Values Spiral Elliptical Irregular Mass (Milky Way = 1) 0.005 to 2.0 0.000001 to 50.0 0.0005 to 0.15 Diameter (Milky Way = 1) 0.2 to 1.5 0.01 to 5.0 0.05 to 0.25 Luminosity (Milky Way = 1) 0.005 to 10.0 0.00005 to 5.0 0.00005 to 0.1 Star Population Old and Young Old Old and Young Interstellar Matter (gas and dust) Moderate Little Plentiful

20. Hercules Galaxy Cluster http://home.earthlink.net/~stanleymm/images/NGC6050sm.jpg

24. Magellanic Clouds LMC, red glows are nebulae in the LMC Clouds from Lake Titicaca, Bolivia http://www.ctio.noao.edu/~mcels/gallery/lmc.1.jpg

25. Magellanic Clouds & Milky Way http://www.atnf.csiro.au/news/press/images/magellanic_pics/MSsim_labels.jpg

26. Milky Way & Clouds in infrared from 2MASS http://astsun.astro.virginia.edu/~mfs4n/sgr/2mass_allskyatlas.jpg http://astsun.astro.virginia.edu/~mfs4n/sgr/sgr.flyaround.mpg

28. Andromeda Galaxy (M31, M32, M110)

29. Andromeda Constellation Locate M31 and M33

30. Triangulum Galaxy (M33)

31. M33 The pink glow of emission nebulas can be seen in this photo

33. Center of Virgo Cluster Virgo Cluster near M84, M86 M86

34. Sombrero Galaxy (M104) from HST

36. Large-Scale Structure of the Universe http://www.astro.princeton.edu/~cen/PROJECTS/p1/DARKallz0.jpeg Sheets & Voids: http://heasarc.nasa.gov/docs/cosmic/sheets_voids.html

40. 3C 273-Quasar HST image of 3C 273 showing disk details (quasar blocked) 3C 273 Starfield in Virgo 3C 273 is one of the first identified quasars, it resembles an 11 th magnitude star in Virgo and is visible in small amateur telescopes