Bright moons

[Laurefindel]

There is a sun, but the planet is tidally locked to its sun and the campaign’s world is on the perpetually dark side. The moon, which orbits the planet, reflects that sun’s light normally.

There is a sun but it does not radiate light. It radiates something else. The surface of the moon is coated with a substance that reacts to the sun’s emissions, emitting light as a result.

There no sun but there are countless distant stars. The moon reflects and amplifies starlight, because magic.

There is no sun but there used to be one. The moon keeps emitting residual light it has absorbed for so long, because magic.

 

[Baron Opal II]

Black holes, in and of themselves, do not emit much radiation. That's why they are black.

Right, but...

If you have matter falling into the black hole, that will heat up as it falls in,a nd glow, and that can give you a light source.

But that also means that your planet is in the accretion disk of a black hole, which doesn't seem like a wise place to be.

That's what I was thinking. There can be significant radiation coming from the accretion disk. That might act with the magnetic field of the planet or the moons themselves. At a survivable distance, of course. If the radiation from the black hole's disk will be too diffuse at an AU, then that won't work.

But, ways to have the moon be bright:
The thing is still molten, and glows with its internal heat.
The moon has a really, really intense magnetic field, and it glows in the light of its own aurora.
The moon is largely covered by an ocean filled with bio-luminescent algae/plankton.

Great ideas, thanks!

 

[Baron Opal II]

Is it a (scientific) planet or (fantastical) "world?" Meaning, is it a planet that, except for magic, follows the current known laws of physics? Or is it a world that need not follow any laws of physics?

Physics with added magic. If I can have a method that follows physics, even with a little magical "help", that's preferred.

The "moon" is a hole in the sky through which a glimpse of another world is visible.

Neat idea! Thanks.

Studies suggest that the ice of Jupiters moon Europa glows faintly due to bombardment from Jupiters intense radiation field.

Also on Jupiter's moons Io is the most volcanically active moon in the solar system and thus emits a strong infrared glow (but human eyes cant see it, but who says your characters all have human vision?)

Another option is that the moon is covered in a bioluminescent covering (an algae slime?, plant cover?)

Cool ideas! Thanks.

How do your fantasy farmers grow crops without a sun? Do you basically just have a surface Underdark, where fantastic mushrooms make up the basis of every diet?

Good question! Yes, fungi make up a significant part of the diet. There are also farms where starlight is collected. There are natural streams of starlight collections. There are occasional gloaming flows where a stream of starlight flows across the countryside. There can be quite problematic when they encounter habitations.

There is a sun, but the planet is tidally locked to its sun and the campaign’s world is on the perpetually dark side. The moon, which orbits the planet, reflects that sun’s light normally.

There is a sun but it does not radiate light. It radiates something else. The surface of the moon is coated with a substance that reacts to the sun’s emissions, emitting light as a result.

There no sun but there are countless distant stars. The moon reflects and amplifies starlight, because magic.

There is no sun but there used to be one. The moon keeps emitting residual light it has absorbed for so long, because magic.

Neat ideas! Thanks. I've got a tidal locked planet already in the greater system, so that's covered.

 

[aramis erak]

Black holes, in and of themselves, do not emit much radiation. That's why they are black.

If you have matter falling into the black hole, that will heat up as it falls in,a nd glow, and that can give you a light source.

But that also means that your planet is in the accretion disk of a black hole, which doesn't seem like a wise place to be.

Technically, a black hole emits no radiation. Unless gravity is a radiation (which it appears not to be) instead of a deformation of spacetime. (Hawking Radiation has not been observed; Unruh Radiation's observation has been widely criticized, and is prerequisite to Hawking Radiation...)

There's little reason a world cannot be in a stable orbit around a black hole, being kept warm by a thin stream of accreting material forming a weak accretion disk – say, an ice-giant or gas giant being stripped – in a closer orbit.

Or, orbiting a Class L star - a dim reddish star, which puts out mostly IR, and would make for a comfortable but very dark setting. There is a chlorophyl analog for the upper IR range...

 

[Umbran]

Technically, a black hole emits no radiation. Unless gravity is a radiation (which it appears not to be)
instead of a deformation of spacetime. (Hawking Radiation has not been observed; Unruh Radiation's observation has been widely criticized, and is prerequisite to Hawking Radiation...)

I'm a physicist, so you are trying to teach your grandmother to suck eggs. My words were chosen carefully, for good reason - to classify all the other bits that people might have heard of into a chunk that could be disregarded for purposes of this discussion.

And, if you want to get REALLY technical, we have detected gravity waves radiated by black holes, so it is radiation. It just isn't the electromagnetic, alpha, or beta radiation we more frequently see.

So, have your egg back.

 

[Cordwainer Fish]

And, if you want to get REALLY technical, we have detected gravity waves radiated by black holes

If you want to get really really technical, they're gravitational waves; gravity waves are something different and much more mundane (waves on water are gravity waves).

 

[Umbran]

If you want to get really really technical, they're gravitational waves; gravity waves are something different and much more mundane (waves on water are gravity waves).

If you want to be REALLY really really technical, both "gravity" and "gravitational" are correct. The former is merely ambiguous, but will generally be resolved by context.

I don't think there's been any cases yet in which we see waves coming from a stellar-mass, compact object that is immersed in a dense fluid for there to be a lot of question on the point.