Where can I put images of other planets so that they are not local to my machine. I noticed the default images are from their S3 bucket.
Not sure what you mean with "so that they are not local to my machine", if you would like to use your own images, you would need to put them on some host service, for example: http://imageshack.com/
The image you used from their server is just a blue circle. If you create a div, put background color to it, and make it round (radius:50%) you just created another planet. Another option is instead of making a div for every planet you want to add, you just browse the internet for planet pictures and insert them using the comand img src "url of the image here ".