What happens is that your camera tries to expose the whole frame properly and since you have two very contrasting elements, the camera does not know what to do. You have a black (or almost black) background, but the camera does not readily know that - it probably falls out of its metering range. If this was a night landscape, exposing a little more than the lowest thing the camera can meter can get you somewhere even in Auto. But since you're shooting [for] the Moon, it comes out overexposed.
The simplest thing you can do is switch to spot metering. If you don't know how, look at page 9 of the manual - it should work even in Auto. Don't forget to switch it back to Matrix when you're done shooting the moon - spot can give you some unexpected results in "normal" shooting situations.
If you're willing to try manual mode, go on. An example starting point would be ISO 100, f/7.1, 1/320 (but that's, of course, just a wild guess). From there, depending on if it's under- or overexposed, start increasing or decreasing the shutter speed until you have proper exposure. The slower you go, the bigger is the risk to introduce blur from camera shake; use a tripod and a remote shutter if you can (and turn off VR if you do).