Hi, new to the forum. Really not an expert in astronomy, science fiction or the like but I'm trying to add science fiction aspects to a fantasy-oriented world and was hoping for some input/verification of facts.
I know there's a lot of exotic stuff out there and an infinite number of possibilities to consider. I just really would like to have one habitable moon with an earthlike composition, with a smaller moon system and/or ring, orbiting one gas giant with one Sun-sized star. Let's say theoretically we start with a Mars-sized satellite or larger in a close orbit maybe the distance of our moon. As I understand it the planet/satellite ratio for Jupiter and Saturn is about 5000:1. Therefore the parent planet would have to be heavier than Jupiter if the moon was the size of Mars.
The moon would be tidally locked of course, and the planet could fill up as much as 10° of the sky (as I understand it, allegedly). It would also be very bright at night, as I understand it (allegedly) if the planet had reflective water vapor clouds. From what I've read it could be as much as a thousand times brighter than our moon, which would be like an LED-lit interior of a home – perhaps brighter than the day side.
Does this sound accurate? Also is it even realistic that a moon could orbit close-in to a gas giant? Would it become too vulcanized or torn apart by the Roche limit so need to be more of a distant orbit to support life, which in turn would dim things? How would radiation and magnetism affect life? Is it even a realistic question to ask if life could form on a moon orbiting a planet? I will note that Avatar had floating mountains, so don't be too harsh.
Lastly as I understand it there would be daily eclipses that could last for several hours during certain seasons (spring/summer). I'm just trying to get a grasp on how dark the sky would get during the eclipses. Twi-lightish or pitch black? I'm not trying to be precisely scientific about this. My life might wither up and die quickly in real life, but I want to try and get things as accurate as I can and maybe start up a discussion.