The most sensible such situation is having the action happen on a moon of a smallish gas giant. Something a bit smaller than Saturn could hold an earth-sized mo

The most sensible such situation is having the action happen on a moon of a smallish gas giant. Something a bit smaller than Saturn could hold an earth-sized moon in close enough orbit to have reasonable day-night cycles even if it's tidally locked. (And those days would be a bit freaky -- unless it had a very high inclination, in such a close orbit around such a large body, there would likely be an eclipse every day at midday.)