Saw a link to a tutorial on how to make these little wonders from Pano's over at http://revellphotography.com/blog/ yesterday. So I had to give it a spin, I did have to do some extra steps with mine as the horizons did not match equally, but that what a tutorial is for. To get you started in a direction, where you end up is your interpretation. I used a Pano form San Fran and Skyline Dr.
You can see a third planet I did from Great Falls (my personal favorite of the three) over at http://www.jasondmoore.com/blog/ for his weekly Geographic Composition.