* It is possible to rotate.
The planisphere rotates when you drag with the mouse.

* Direction
The front of starry sky that the lower side of planisphere sees now.
The center of planisphere is a zenith.
Opposite of starry sky that the upper part of planisphere sees now.

Is it a display only the [N] stands out why?
When you see the screen, you understand the direction at once.

* Convenient function
If the [N],S,E,W is clicked, the direction becomes front at once.

* Rotation

It is possible to rotate with the mouse like this.