Make sure to get the right version. There is the iPhone only, and the iPad/Universal variants. The link in the display to the right is the iPhone only version. For the iPad/Universal version go to:
http://itunes.apple.com/app/distant-suns-for-ipad-astronomy/id363418936?mt=8
Why to separate products? Due to many factors, Distant Suns for the iPad is currently a separate product from Distant Suns/iPhone, meaning no free upgrade for the time being. There was a lot of discussion on the boards about the benefits or problems of making apps “universal” (one app that runs on iPhone and iPad) or specific to the device.



