The new iPad version of the app (v 1.13) supports the entire iPad screen. The main Seestar screen remains in portrait mode even when the iPad is rotated to landscape orientation. I now see that this is by design. Once you enter one of the viewing modes (Stargazing, etc.), if you rotate the iPad to landscape orientation, the Seestar app also rotates to landscape orientation.
Just make sure "Rotation lock" is OFF on your iPad. Thanks ZWO!