GF1: How to manual focus on infinity

I'm trying to photograph the night sky and my ability to focus on infinity in the dark is a real hit and miss.  I'm using either the 20mm or the 14mm Lumix lens.  I try to AF on the moon or distant object, then switch to MF, but the camera will not always AF at night.  Trying to manual focus is very hard to do in the dark.  Any suggestions?  Thanks.