Hi Patty
I've taken a few of this type of picture and can relate my experiences.
These, and a few others like them, were taken on a cloudless night (at least the moon was out when I took the shots) with a full moon. The aperature was set at F 9.0 and the shutter speed was for 30 seconds at ISO 200. One thing about the camera that I used (Canon 300D) was that the longest I could hold the shutter open was 30s without resorting to holding down the button myself or using a remote switch (which I don't have). If it was cloudy, I would've changed the ISO to 800, set the aperature to 4.0 and see if that would work. Increasing the ISO make the sensor more sensitive and decreasing the aperature setting means the shutter is open wider than at higher numbers. This would've made up for the absence of the bright moonlight.
Also, it was cold! Remember that this will drain your battery quicker, so be prepared! Another trick is to use the timer setting on the camera so the start of the 30 s is automatic and not you pressing on the shutter release button (which may shake the camera enough to blur the shot).
Best of luck to you!
Cheers
Stuart
I'd give my right arm to be ambidextrious.
Comments and criticisms on my galleries more than welcome!