Today on Crash Course Astronomy, Phil dives into some very dark matters. The stuff we can actually observe in the universe isn’t all there is. Galaxies and other large structures in the universe are created and shifted by a force we detect mostly indirectly, by observing its impact: DARK MATTER.

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Chapters:
Introduction: Dark Matter 00:00
Discovery of Dark Matter 0:55
What is Dark Matter? 3:50
Axions 4:33
Gravitational Lensing and the Bullet Cluster 5:15
What Effect Does Dark Matter Have on the Universe? 8:50
Review 10:48
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PHOTOS/VIDEOS
Virtual tour in our Solar System (Artist's impression) http://www.spacetelescope.org/videos/... [credit: ESA/Hubble (M. Kornmesser & L. L. Christensen)]
Hubblecast 11: A grand design in a galactic festoon http://www.spacetelescope.org/videos/... [credit: ESA/Hubble (M. Kornmesser & L. L. Christensen)]
Hubble's High-Definition Panoramic View of the Andromeda Galaxy http://hubblesite.org/newscenter/arch... [credit: NASA, ESA, J. Dalcanton, B.F. Williams, and L.C. Johnson (University of Washington), the PHAT team, and R. Gendler]
Panning and zooming on Abell 1689 http://www.spacetelescope.org/videos/... [credit: ESA/Hubble (M. Kornmesser & L. L. Christensen)]
All-sky image of molecular gas and three molecular cloud complexes seen by Planck http://www.nasa.gov/mission_pages/pla... [credit: ESA/Planck Collaboration]
How to Become a Star http://www.eso.org/public/images/eso0... [credit: ESO]
Neutron star illustrated https://commons.wikimedia.org/wiki/Fi... [credit: NASA, Casey Reed - Penn State University]
Alone in Space - Astronomers Find New Kind of Planet http://www.nasa.gov/topics/universe/f... [credit: NASA/JPL-Caltech]
Black hole deforms space http://www.spacetelescope.org/videos/... [credit: ESA/Hubble (M. Kornmesser & L. L. Christensen)]
Gravitational lensing in action http://www.spacetelescope.org/videos/... [credit: NASA, ESA & L. Calçada]
Bullet Cluster http://apod.nasa.gov/apod/image/0608/... [credit: X-ray: NASA/CXC/CfA/ M.Markevitch et al.; Lensing Map: NASA/STScI; ESO WFI; Magellan/U.Arizona/ D.Clowe et al. Optical: NASA/STScI; Magellan/U.Arizona/D.Clowe et al.]
Bullet Cluster, Optical http://chandra.harvard.edu/photo/2008... [credit: NASA/STScI; Magellan/U.Arizona/D.Clowe et al.]
Bullet Cluster, X-ray http://chandra.harvard.edu/photo/2008... [credit: NASA/CXC/CfA/ M.Markevitch et al.]
The Bullet Cluster http://www.esa.int/spaceinimages/Imag... [credit: X-ray: NASA/CXC/CfA/M.Markevitch, Optical and lensing map: NASA/STScI, Magellan/U.Arizona/D.Clowe, Lensing map: ESO WFI]
Pandora’s Cluster — Clash of the Titans http://www.nasa.gov/mission_pages/hub... [credit: NASA]
Hubble Refines Distance to Pleiades Star Cluster http://hubblesite.org/newscenter/arch... [credit: NASA, ESA and AURA/Caltech]
Stephan’s Quintet http://apod.nasa.gov/apod/ap120225.html [credit: Hubble Legacy Archive, ESA, NASA]
Virgo Cluster Galaxies http://apod.nasa.gov/apod/ap150804.html [credit: Rogelio Bernal Andreo]
Illustration of the distribution dark matter in the Universe http://www.nasa.gov/mission_pages/hub... [credit: NASA, ESA, and E. Hallman (University of Colorado, Boulder)]