How to get current android orientation?

I need to change the “Field of View” option (or “Aspect Ratio”, I haven’t figured out yet) regarding android device orientation. For example, if orientation is Landscape, so I will 90 degrees of Field of View, but if it’s Portrait, I’ll use 45 degrees.

How can I determine the current orientation of an Android device and, moreover, if possible, how to bind it to an event like “OnChangeDeviceOrientation” (when the device changes its orientation by user)?