Why is it Dark at Night?

Have you ever wondered why you look up and see a dark sky at night?Help share science with the world: http://translate.minutephysics.comSubscribe to MinutePhysics! http://dft.ba/-MPsubscribeMinutePhysics is on Google+ - http://bit.ly/qzEwc6 And facebook - http://facebook.com/minutephysicsAnd twitter - @minutephysicsMi nute Physics provides an energetic and entertaining view of old and new problems in physics -- all in a minute!Music by Nathaniel SchroederThanks to Nima Doroud and Niayesh Afshordi for contributions and to Perimeter Institute for support. http://www.perimeterinstitute.ca