I had no idea that WikiSky existed, but I love it. The site features fabulous images from NASA-funded scopes the world round.
This ribbon of gas is the remnant of a supernova:
Oh bubble overlords, let me be the first to welcome you to Earth. I kneel before thy bubbly, refreshing greatness.
Update: Tyler Cowen’s commenters, ahem, burst my bubble. Apparently this is some kind of nebula (although “God’s contact lens” was a good suggestion). Personally, I like my explanation better. And I take comfort in the knowledge that the nebula-boosters will be the first to get it when the overlords land.
The commenters are worth reading in full.