Hello. I want to start taking some long-exposures at night, generally of dark landscapes, but perhaps later trying some star and moon shots, etc. I'm very much a photography beginner in general, and was wondering if anybody had any advice on some general guidelines for the sorts of exposure times required for different situations, f/stop to be used, etc. Is a light-meter necessary for that sort of thing? Or does that not apply once you're attempting exposures that are minutes or hours long? Thanks!