I wonder if there is a stable star-moon-planet system where a specific area of the planet would be permanently covered by shadow. I'm not looking for a common tidally locked planet with a roughly 50% dark zone. This is the desired order of preference for my world:
Most of the planet has a traditional day-night cycle, except for some area which is always covered by night (like the Australia continent, or China).
Most of the planet has a traditional day-night cycle, except for one or more vertical stripes of it (ex: GMT-3 is always covered by shadow).
Instead of a tidally locked 50% covered by shadow, say, 25% is permanently covered by shadow, 25% is always bathed by sunlight, and the other 50% has a day-night cycle.
Ok, I give up. Just a tidally locked planet between two stars, so there are two 25% areas covered by shadow and 25% in-between with light. Is this possibly stable?
I'm willing to allow any non-conventional (but non-magical) feature to this system: large moons, more than one sun or even a torus planet topology.