And yes, long exposures from 13-15 seconds (the first = 15 seconds), and ISO around 400. The lens is a Tokina 11-16mm (11mm, f/2.8 focused manually to infinite). Also, the viewfinder covered to avoid light behind the camera from getting through to the sensor. While I could expose the images longer, I prefer not to overexpose the highlights. Therefore my photos are slightly underexposed, but since I use CS5 I just take care of this problem when processing.
Now, every situation is different. For example, on a full moon even 13 seconds is often too long, unless there is a nice foreground or something that I want to include in the photo. All I am trying to say is that you have to try different camera settings depending on how much light or darkness there is considering the main subject (in my case, the Auroras). So, think of ISO speeds from 400 to 800, and lens apertures from f/2.8 to perhaps f/5, and exposures from 10 seconds to 20 seconds. There aren't specific rules to follow. You just have to try different settings until you figure which ones are the right ones at the moment.
Did you take those by the Flood Channel in North Pole? I stopped-by around 11:00 PM when the lights looked their best I have seen recently, but there were a bunch of people driving up with their headlights on. I have to move farther down the road to another spot, so I missed that best opportunity But at least I took a whole bunch of good ones by the Steese past Pedro Dome (on top of the hill up there).