SciFi details

I was watching a SciFi production a little while ago and I noticed something, it was a night time scene with three moons and the three moos were all full.  And I realized that it was wrong.  One moon on the left and one on the left and one in the center.  That was wrong. It would not have mattered if it had been new for that matter, of half moons.  It was wrong.  The reason was because the were in different parts of the sky and therefore could not be the same phase.  A full moon is opposite the sun in the night sky and a waxing or waning moon when it is thin is close to the horizon.  New moons close to the setting sun and waning moons closer to the rising sun.  Half moons are half way between the full and the horizon depending on whether they are waxing or waning.  So if you see two moons in the sky and they look like the same shape. They had better be in the same part of the sky.

Which brings up another thing, in my setting world there are three moons.  There were six originally but I thought paring the number down might be easier for my players.  One has about the same orbital period as our own moon, which means that it is about the same distance, roughly.  The setting world is a lot larger and more mass, which means that the moon must be further away and going faster, but roughly the same in other ways.  The first moon is much closer and has an orbital period of about half of our moon, so that means as I said: it is closer.  The third moon has an orbital period three times as long as our moon, so it must be much further out.  Cool I think, but it adds a few things that I did not consider first.

The first moon is green, so that means it has a higher albedo than our moon.  It is habitable, the green is vegetation.  That means there must be clouds, so it is mostly green.  So the albedo is probably somewhere between 90-30 or 60.  That is about six times as bright as our moon, but it is closer too so that means, using the inverse square law, it is 4 times that, or 24x as bright Earth's moon. 

There is more. 

The full moon almost always is eclipsed by the planet.  Because the planet is bigger than Earth and the moon is much closer.  It will be passing into the shadow when it is full every time.  The planet is about ten times surface area.  The shadow of the planet is roughly ten times bigger too, the radius is only three times though.  That would mean that full moon would be in eclipse roughly 40x as frequent as our own moon.   That would mean it would always be in eclipse when it was full.  On the other hand, solar eclipses are a different thing altogether.  The moons appear the same size as each other, which means they would occur about as frequently as they do on Earth, except there are three suns.  So three times the chance, but only two times during the year would ere be a chance of a Earth style solar eclipse, unless all the moons were to eclipse the three suns simultaneously.  The two times are in the winter when e blue sun eclipses the other two suns and the high summer when the other two eclipse the blue sun, but only two days, as they eclipse each other.  Other times and eclipse would not reduce the light much. The eclipse would look like the one sun disappearing and the light not changing.  For a lunar eclipse the light of the Full moon would drop from 24x to only 2-3x or zero.  It would also turn a deep blood red too.  Cooler still because it is the moon of the evil god.

The second moon is the Blue moon.  As said it is roughly where the moon is on Earth.  The albedo is 30, or it is three times as reflective as our moon.  It is also a place of life, but with oceans.  So there is also 50% cloud cover, so roughly 60 albedo for six times as bright.  Tone it down a little to make it bluer, make it 4x as bright.  Lunar eclipses would be ten times as likely, or about one of three full moons.  

The third moon is further away than the moon, about three times the distance, so with the inverse-square laws, 1/9 as bright as our own moon, but it is a white moon with snow and nearly 100% cloud cover, so an albedo of 90.  So the moon is just as bright as our moon.  

What is the night sky like then.  When the skies are clear, the night is brighter.  When the green moon is just off full, the light would count as dim light, the blue full moon would be three times as bright as our clear full moon.  Our full moon will cast a shadow with its light.  So count it in full moons of light.  The white moon would be 1 when full.  The blue moon was 3 when full and a half moon 1.5. New and old it would be .3.  The green moon, would never be 24, because of the full moon eclipse, but it would be 20 on the nights before and after.  When it is new or old, it would be a 2.  New and old moons are bright only at the start or end of nights.

So it would mean that on a typical night, if the skies are clear you would be able to see fairly well at night.  Those with Darkvision in the game would see as if it were bright light.