The Earth orbits the Sun. The Sun orbits the galactic center which takes about 250 million years. Ever wonder what the Earth encounters during that time? I doubt NASA does either.
For extra credit, how does that affect climate?
We’re thirty thousand light years from galactic central point.
We go ‘round every two hundred million years,
And our galaxy is only one of millions of billions
In this amazing and expanding universe.
http://www.youtube.com/watch?v=buqtdpuZxvk