AaS! 007: How do we know that dark matter exists?

How do we know that dark matter exists? Are you sure that scientists aren't just making things up because they're lazy? What makes it dark anyway? I discuss these questions and more in today's Ask a Spaceman!

Keep those questions about space, science, astronomy, astrophysics, and cosmology coming to #AskASpaceman, Twitter@PaulMattSutter, http://www.Facebook.com/PaulMattSutter, and http://www.askaspaceman.com for COMPLETE KNOWLEDGE OF TIME AND SPACE! Music by Jason Grady and Nick Bain.