I have a screenplay project I'm working on that has quite a few similarities with this thread (and thanks to everyone on that thread, including poster). So it's set on a moon orbiting a Hot Jupiter. The level of research I'm doing may seem a bit excessive, but over-researching is part of my process. I've figured out the basic parameters, but the main problem I'm having is figuring out light levels. This is pretty complicated, so I'm really just trying to figure out reasonable limits and consequences.
For convenience's sake, I've so far assumed that the planet is about 1.1 AU from a G-class star (orbital period about 419d), though I might modify this. The parameters at present are (approx):
Planet mass = 2e28 kg
Moon mass = 2e24 kg
Semi-major axis (moon) = 3e6 km
Orbital period (moon) = 10.3 days
Moon radius = 4000 km
I've maxed out the gas giant size in order to have the largest possible moon, and placed it far enough away that with a thick atmosphere the radiation from the planet should hopefully not be too harmful. Despite the mass, I'm assuming the planet size is about identical to Jupiter. If I've calculated angular diameters correctly (planet = 163.86', sun = 32' for simplicity), the planet will be about 5 times the size of the sun in the sky and there will be a maximum of about a 1h53m mid-day eclipse (total darkness about 1h10m). I'm also thinking the moon will be quite small and dense, so that this might get me close to Earth gravity without Earth size. I calculate the gravity to be about 8.34 m/s^2 (I so far haven't tried to figure out if the planet's gravity would have a substantial effect on this #).
The efforts of anyone checking my math are much appreciated, as well as any suggestions anyone might have. My main question at this point, however, is about luminosity. This question came up in the Day/Night thread, but it didn't go into detail. It was merely suggested that the night-time light from the planet would be some 4000 times as bright as the
sun. EDIT: MOON! Oops. My research indicates that it depends primarily on the albedo of the reflecting body and the atmosphere, right? Just taking the arbitrary 4000xfull moon number, that would create a night sky about equivalent to a very overcast day (~1080 lx), which is pretty bloody bright. With about 2h of actual darkness, this moon will have about 5 day "nights," which I'm looking to have more of an eternal twilight effect. If it helps, I'm thinking the atmosphere will be pretty thick (this is largely due to light terraforming) with a lot of particulates that give the sky an indigo hue (the particulates are important to the plot, the color to the aesthetic). What are the lower bounds I can put on my giant nightlight? I'm thinking I might not have much room to play with the albedo, b/c gas giant composition is pretty regular, right? How much can atmosphere adjust the light? What effects would necessary tweaks have? Already it is tidally locked, obviously, so I'm assuming extreme tides, pretty much impassable seas (and the moon is mostly ocean, b/c of water picked up on the Hot Jupiter's passage into the habitable zone). Possibly very little seasonal variation due to the water and atmosphere? I haven't decided on axis-tilt and various weather-related details (which will effect the exact latitude of the inhabitants).
Oh, and one other question: would the orbital radius have a large effect on weather on the moon? As compared to the planet's orbit, the moon's orbit would be like a squiggly line as it followed the planet around, and so far I've assumed this variation wouldn't have significant effects on seasons or temperatures in comparison to axial tilt and the planet's own eccentricity, but I'm not quite sure.
Many thanks in advance for any help you can offer.