Active galaxies pour out lots of energy, due to their central supermassive black holes gobbling down matter. Galaxies tend not to be loners, but instead exist in smaller groups and larger clusters. Our Milky Way is part of the Local Group, and will one day collide with the Andromeda galaxy. Clusters of galaxies also clump together to form superclusters, the largest structures in the Universe. In total, there are hundreds of billions of galaxies in the Universe.

Crash Course Astronomy Poster: store.dftba.com/products/crashcourse-astronomy-poster

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Table of Contents
Black Holes at the Center of Galaxies 2:26
Galaxies Are a Part of Small/Large Clusters 9:47
The Milky Way is Part of the Local Group 6:45
Galaxy Clusters Clump Together to Create Superclusters 11:03
Hundreds of Billions of Galaxies 12:39

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PHOTOS/VIDEOS
Galactic Wreckage in Stephan's Quintet hubblesite.org/newscenter/archive/releases/2009/25/image/x/ [credit: NASA, ESA, and the Hubble SM4 ERO Team]
Best image of bright quasar 3C 273 www.spacetelescope.org/images/potw1346a/ [credit: ESA/Hubble & NASA]
Nearby Quasar 3C 273 hubblesite.org/newscenter/archive/releases/2003/03/image/a/ [credit: NASA, M. Clampin (STScI), H. Ford (JHU), G. Illingworth (UCO/Lick Observatory), J. Krist (STScI), D. Ardila (JHU), D. Golimowski (JHU), the ACS Science Team, J. Bahcall (IAS) and ESA]
Gamma Rays chandra.harvard.edu/photo/2014/archives/archives_herca.jpg [credit: X-ray: NASA/CXC/SAO, Optical: NASA/STScI, Radio: NSF/NRAO/VLA]
Black hole (artist's impression) www.spacetelescope.org/videos/hst15_black_hole2/ [credit: ESA/Hubble (M. Kornmesser & L. L. Christensen)]
Matter accreting around a supermassive black hole (artist's impression) www.spacetelescope.org/videos/hubblecast43c/ [credit: ESA/Hubble (M. Kornmesser)]
Artist’s animation of galaxy with jets from a supermassive black hole www.spacetelescope.org/videos/heic1511a/ [credit: ESA/Hubble, L. Calçada (ESO)]
NASA's Swift Finds 'Missing' Active Galaxies svs.gsfc.nasa.gov/cgi-bin/details.cgi?aid=10698 [credit: NASA/Goddard Space Flight Center]
Sagittarius A*: NASA's Chandra Detects Record-Breaking Outburst from Milky Way's Black Hole chandra.harvard.edu/photo/2015/sgra/ [credit: NASA/CXC/Amherst College/D.Haggard et al]
NASA Hubble Sees Sparring Antennae Galaxies www.nasa.gov/content/goddard/nasa-hubble-sees-sparring-antennae-galaxies [credit: Hubble/European Space Agency]
A New Dawn svs.gsfc.nasa.gov/cgi-bin/details.cgi?aid=11011 [credit: NASA, ESA, G. Besla (Columbia University) and R. van der Marel (STScI)]
Galaxy Sky svs.gsfc.nasa.gov/vis/a010000/a011000/a011011/hs-2012-20-h-full_1920x1080.jpg [credit: NASA, ESA, Z. Levay and R. van der Marel (STScI) T. Hallas, and A. Mellinger]
Virgo Cluster deepskycolors.com/astro/2015/06/RBA_VirgoCluster3p_2048.jpg [credit: Rogelio Bernal Andreo]
Cosmic Clumps svs.gsfc.nasa.gov/cgi-bin/details.cgi?aid=11445 [credit: NASA's Scientific Visualization Studio]
Laniakea: Our Home Supercluster of Galaxies apod.nasa.gov/apod/ap140910.html [credit: R. Brent Tully (U. Hawaii) et al., SDvision, DP, CEA/Saclay]
Webb Science Simulations svs.gsfc.nasa.gov/vis/a010000/a010600/a010663/index.html [credit: NASA/Goddard Space Flight Center and the Advanced Visualization Laboratoy at the National Center for Supercomputing Applications]
Hubble Deep Field upload.wikimedia.org/wikipedia/commons/5/5f/HubbleDeepField.800px.jpg [credit: R. Williams (STScI), the Hubble Deep Field Team and NASA]
Hubble Ultra Deep Field 2014 hubblesite.org/newscenter/archive/releases/2014/27/image/a/ [credit: NASA, ESA, H. Teplitz and M. Rafelski (IPAC/Caltech), A. Koekemoer (STScI), R. Windhorst (Arizona State University), and Z. Levay (STScI)]

1. Introduction to Astronomy
2. Naked Eye Observations
3. Cycles in the Sky
4. Moon Phases
5. Eclipses
6. Telescopes
7. The Gravity of the Situation
8. Tides
9. Introduction to the Solar System
10. The Sun
11. The Earth
12. The Moon
13. Mercury
14. Venus
15. Mars
16. Jupiter
17. Jupiter's Moons
18. Saturn
19. Uranus & Neptune
20. Asteroids
21. Comets
22. The Oort Cloud
23. Meteors
24. Light
25. Distances
26. Stars
27. Exoplanets
28. Brown Dwarfs
29. Low Mass Stars
30. White Dwarfs & Planetary Nebulae
31. High Mass Stars
32. Neutron Stars
33. Black Holes
34. Binary and Multiple Stars
35. Star Clusters
36. Nebulae
37. The Milky Way
38. Galaxies, part 1
39. Galaxies, part 2
40. Gamma-Ray Bursts
41. Dark Matter
42. The Big Bang, Cosmology part 1
43. Dark Energy, Cosmology part 2
44. A Brief History of the Universe
45. Deep Time
46. Everything, The Universe...And Life
47. Explore The Solar System:

In this Crash Course series, marvel at the wonders of astronomy with your host for this intergalactic adventure, the Bad Astronomer himself -- Phil Plait. In just 40 short lessons, you will learn the basics of the oldest science known to humanity.

Be sure to check out links to relevant Photos in the description for each video.