Rebel XT - Focus to infinity?

[Beltaine]

I just got a DRebel XT, with the kit lens. I was trying to take some nights shots of a front coming in last night, and never could get the shutter to fire. The camera would focus, but the green light would never go steady. I was shooting up at the sky so there really was nothing for it to hit to focus on, but I figured at that point it would assume to focus all the way out. I ended up switching to MF and doing it that way.

Is that just what I'm going to have to do, or am I missing something?

[another view]

Autofocus systems have to "see" something to focus on. They focus by looking for edge contrast - like the edge of a building or something else that stands out. The less contrast (not talking about exposure here), the less of a chance of it working. Also, the lower the light level and slower the lens, the less likely it will be to get accurate focus.

An open sky has nothing to help an AF system, so the choices would be to look for something in the distance - maybe a water tower or a building and then holding the shutter button down halfway to lock the focus and re-compose (unless the camera has another option), or doing what you did which is to switch to manual focus.