If you just want a realistic moon lighting your landscape, you have to take a bit of a detour. You can create a 2nd planet, and set that in the view. You can also set the sun below the horizon, behind the camera, and move it around for the right lighting on the moon.
But for the light that should come from the moon, you have to create a lightsource that you should place between the earth and the moon (about in the middle, a bit more toward the earth). Then maneuver it exactly in front of the moon, from camera perspective, and enlarge the radius until it seems to be as big as the moon. Now increase the strengt of the light to rediculous big numbers, like 1e8, or even 1e9...
If it works correctly, the light has allmost no noticable effect on the moon (because the moon is also lighted by the sun), an your landscape should be lit like moonlight.
If the effect on the moon is more visible than desired, move the light closer and adjust the size again.
