When doing Landscape Astrophotography the major methods of illuminating the landscape at night include:

1) the existing ambient light or "starlight" This includes starlight, light pollution, and airglow,

2) Moonlight.

3) Low Level Lighting.

4) Light Painting.

5) Occasionally on cloudy nights the existing light pollution may serve as the primary source of lighting. 

Below is a brief discussion of some of these types of lighting.