Samuel Barber's Adagio For Strings, Op. 11: Angus Dei - performed by The Choir Of Trinity College, Cambridge.
It is a perfect accompaniment for the beauty and solitude of space as this piece is both beautiful and somber.
Some of the movie clips used:
Comet with dust jets
Helix planetary nebula and the creation of planetary knots
Helix Nebula and formation of the Helix Nebula
Orion Nebula
Cat's Eye Nebula
Egg Nebula
Cassiopeia A
Formation of planetary Nebulae
My sincerest gratitude goes to NASA, ESA and STScI for the use of their movie clips, without their dedication and hard work these videos would not be possible.
In addition, thanks to Stephen Koehler for providing this particular piece. He knew it would work better then the instrumental I had originally used, and he was right.