Okay so we have the case:

  • My world is Earth-like(Spherical)
  • Slight fantasy, but also some science
  • It has a normal day-night cycle and seasons

I need for a particular area to make the sky somewhat bright at night naturally(Magic is a last solution).

You can define what I want as:

  • Local influence, so nothing such as rings
  • It isn't visible during the day, thus not influencing day light
  • It ought to shine like the moon, but only with more light, but also make night understandable. So instead of being a second "sun", it has to keep the sky dark a distance
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    $\begingroup$ like light pollution naturally? $\endgroup$ – ratchet freak Jan 28 '15 at 14:01
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    $\begingroup$ How about using Aurora Borealis as inspiration? en.wikipedia.org/wiki/Aurora $\endgroup$ – Shollus Jan 28 '15 at 14:19
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    $\begingroup$ @Giuseppe How big? $\endgroup$ – MikhailTal Jan 28 '15 at 14:24
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    $\begingroup$ How big is the area you want to light up, around where (long/lat) are you looking for this effect, and is this seasonal or all year around? Twilight in a mountains shadow could work, but it's only be for a summer season in high latitudes $\endgroup$ – Twelfth Jan 28 '15 at 21:24
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    $\begingroup$ @superluminary I need a very small area(City to region level) $\endgroup$ – MikhailTal Jan 29 '15 at 9:23

16 Answers 16


Imagine a planet interlaced with a giant crystalline network. This could either be a single set running straight through the planet, or an actual web of crystal throughout the entire thing. The source is natural - something about your universe encourages gigantic crystal formations under the conditions your planet formed.

While in most places the crystals are underground, they poke out in two locations on opposite sides of the world, appearing as gigantic semi-transparent mountains. During the night, light from the opposite side of the planet transmits through and makes the entire thing glow fairly brightly, lighting up the surrounding area. But during the day the only real source is moonlight, and that's insufficient to light up the mountain more than daylight normally does.

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    $\begingroup$ I would kill to see this in the real world. +1 from me. $\endgroup$ – Kaz Wolfe Jan 28 '15 at 20:45
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    $\begingroup$ Love this idea. Both magical and possible. $\endgroup$ – MikhailTal Jan 28 '15 at 20:50
  • $\begingroup$ Might need a larger world to create crystal like this...a large rock planet that formed and underwent a cataclysmic event that saw the loss of much of this mass leaving behind the crystals could work. I like the idea $\endgroup$ – Twelfth Jan 28 '15 at 21:22
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    $\begingroup$ This solution, while cool, lights up the ground more than the sky $\endgroup$ – Oldcat Jan 29 '15 at 1:00
  • $\begingroup$ If it lights up an area, its okay. Can you profuce a size-to-area effect chart or something? $\endgroup$ – MikhailTal Jan 29 '15 at 7:38

Obviously, Earth's moon moves in the sky and thus would not meet your requirements. However, some moons are tidally locked with their planet, meaning that they stay in the same position in the sky. The Pluto-Charon system is an example of this phenomenon in our solar system. In this case, the moon would never rise on one side of your planet and it would never set on the other.

The system at night would look something like this, with the sun off to the left:

enter image description here

  • At point A, the moon would be always be barely visible on the horizon. Most of the time it would be obscured by clouds, mountains, or trees.
  • At point B, the moon would appear relatively high in the sky, but would never be directly overhead, It would provide notable light.
  • At point C, the moon would always be directly overhead and would be very bright.

I'm guessing that you want the localization of this effect to be much smaller than a whole hemisphere, though, though I propose the following refinement of this model:

Your planet is tidally locked with a largely non-reflective moon with a single, relatively small, highly reflective surface feature directly facing the planet.

Let's say your moon has an enormous, crystalline structure in the middle of its disk:

enter image description here

If the crystal was shaped like a very, very shallow parabolic mirror, it would constantly focus all sunlight falling upon it directly at the planet, effectively forming a spotlight covering an area of the planet's surface equal to the area of the crystal mirror:

enter image description here

  • Point A: Same as before. Moon not normally visible.

  • Point B: Moon is visible in the sky as before. It's up to you on how bright it appears here, depending on how reflective the surface is.

  • Point C: The crystal focuses all sunlight falling onto it into a stream of parallel rays directed at the planet directly under it. It can be arbitrarily bright or localized depending on what properties you choose for the crystal (size and reflectivity).

During the day time, the sun would fall upon the opposite side of the moon, thereby not falling upon the crystal at all.

Hope you like the idea!

Note that the light would disappear during a Lunar Eclipse, but if the inclination of your satellite's orbit is high enough, this would never happen.

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    $\begingroup$ I like the idea, I'm fairly sure the angle of the "beam" would change during the day as the sun moved (since that would change the angle of the incoming light to the reflector). Also when that part of the moon is shadowed by the earth you would get no light (which may be a good or a bad thing). $\endgroup$ – Tim B Jan 29 '15 at 10:21
  • $\begingroup$ I considered something like this (although I was thinking some sort of smaller natural satellite) but the crystal wouldn't always focus on the same spot. Instead it would sweep along the planet depending on where the planet is in the rotation. $\endgroup$ – Dan Smolinske Jan 29 '15 at 15:16
  • $\begingroup$ Alternatively, put the moon at the Lagrangian point L2, so that it's always in the night sky. However, this could be problematic given that it would probably be perpetually eclipsed. $\endgroup$ – El'endia Starman Jan 30 '15 at 21:01
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    $\begingroup$ @TimB However: First, the light is not reflected uni-directionally by moon because it's surface is anything but smooth, also it's not really shiny (think of a white wall: it's white from all directions). Second, the eclipse is rare and short. Third, our moon is strong enough that you see during the night. Imagine it just a bit closer, a bit larger and a bit whiter, and you get a rather nice light source. One more idea: Make your Moon glowing. Like light absorption, matter excitation and light emission (as with your watches or whatever). This would overcome the eclipse problem pretty well. $\endgroup$ – yo' Jan 30 '15 at 23:33
  • $\begingroup$ @yo' Erm, he suggested placing a parabola on the moon so that it doesn't reflect omnidirectionally... $\endgroup$ – Tim B Jan 31 '15 at 0:12

A particular kind of fireflies may be a good way to have a localized and periodical (they light up during mate selection) phenomenon, as needed. Plus, they are cute, romantic and "magical", though not involving magic :-)

A firefly from our Earth make a feeble amount of light based on biochemical reactions. I've seem swarms of these bugs generate a surprising lighting, even if not at the level of a full moon. To get that much light, you'll need to make them more powerful. An idea could be to replace the chemical reaction with matter/antimatter reaction, or chemistry-based cold fusion. This way, a few atoms would suffice, and you could have extremely bright flying LEDs, still keeping them small and cute.

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    $\begingroup$ I'm used to crazy stuff from the site; antimatter powered fireflies is definitely up there in terms of craziness. $\endgroup$ – overactor Jan 28 '15 at 15:16
  • $\begingroup$ The other option - chemistry-triggered cold fusion - actually looks much more plausible. I heard of experiments being made recently on this matter. $\endgroup$ – Giuseppe Jan 28 '15 at 15:23
  • $\begingroup$ We can make them magical. Like, holy fireflies of the god of light or something. $\endgroup$ – MikhailTal Jan 28 '15 at 16:18
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    $\begingroup$ This idea can be expanded to a number of plants and animals. Trees or plants might be sending off seeds or pollen which lights up at night (think of how Groot lights up dark areas in Guardians of the Galaxy), or how the entire forest "glows in the dark" like in Avatar. Or if, for some reason, all the nocturnal wildlife tended to reflect light, the moon might be enough to light the whole area. $\endgroup$ – DoubleDouble Jan 28 '15 at 18:13
  • $\begingroup$ If you want to be more bright, what can be done is simply increase its numbers. If you have enough environment/nature to support them. Maybe they are holy so no people try to eradicate them in their country and their population grow and grow and grow and come so numerous that this country glow in the night. $\endgroup$ – PhoneixS Jan 29 '15 at 11:07

Big giant ice ring around the world would do just fine. Real orbital rings decay over cosmic time, but it could be a crushed captured comet that recently disintegrated.


Hmm on second thought if the rings were small enough they would be in shadow during the night. Make giant rings and/or if you prefer, put them around the moon or another planet. These actually exist, btw. This is how Saturn would look with supersized rings.

To give a sense of scale, see the tiny bright dot by the cloud in the right-hand corner? Not a smudge on your screen, that's the Moon.

PS: Just noticed you want local influence. Ugh. Try fluorescent stratospheric fungi, feeding on water vapors, desert dust and sun. Kinda like bioluminescent algae below, but in the sky! Hong kong algae


Make your inhabitants see more wavelengths

Why not cheat a little, in the name of creativity?

The human vision system is, although more advanced than many terrestrial creatures, rather limited in the grand scheme of things. This is the size of the visible light spectrum compared to the entire known EM spectrum:

EM spectrum

Richard Dawkins described this as a "gigantic black burka", that we are blind to so much and most of us don't realise this. Once you do, it seems rather anthropocentric to assume things like "night is dark".

The night sky looks very different in other wavelengths. Here's an example, of the X-ray range:

x-ray night sky

Contrast this to the regular visible light image:

visible light night sky

There's a blog post here: http://blog.professorastronomy.com/2010/06/astro-101-electromagnetic-spectrum.html which includes many more images as well as a video slide show.

Note that many animals can see further into the infra-red and ultra-violet ranges, so even without the benefit of fantasy/magic, you can plausibly explain this, for example your inhabitants evolved from nocturnal ancestors.

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    $\begingroup$ This doesn't work for localized illumination though. You could perhaps tweak things to explain that only a certain group of people evolved this trait, but then visitors to the area would not see better in the dark, and those with the improved night vision would have it no matter where on the planet they travel. $\endgroup$ – Doktor J Feb 1 '15 at 4:38

I used something fairly exotic for one of my RPG games. I needed a "always sunny" location on my world, without resorting to (obvious) magic. My world was moderately magical, so some strange stuff was commonplace and I could throw some physics over the window.

I created extremely complex cave system that ran everywhere underground. Those caves were large, and all of them connected to a single point under a huge island in the middle of the ocean. Those caverns were dug out by a now extinct species of giant worms.

The trick was, those worms secreted a special substance to prevent the tunnels to collapse. This substance was initially viscous, but in contact with the air it changed to a solid, silvery layer over the stone. When the sun touched the entrance of a cave, all the cave system would light up!

On that island on the middle of the ocean lived a king that had an idea. He called all of his architects, and asked for a way to use that light to light up the kingdom to keep the beasts away. His architects them created a very tall tower over the cave, lined with mirrors. On the top of this tower was a huge prism, that sprayed the light all around like a very powerful lighthouse.

Didn't matter where the sun was. He was always touching several caves, and so always bathing the kingdom in intense sunlight.

It is a bit... over the top, I know, but the suncaves gave me a fair amount of material to play with my group.

  • $\begingroup$ @BrianS thanks. English is not my first language :p $\endgroup$ – T. Sar - Reinstate Monica Jan 28 '15 at 20:44

If a glowing mountain is accepatable you could use rubber science to have a mineral that in the presence of UV light undergoes a photochemical reaction and without it becomes chemiluminescent. Realistically it would produce some light during the day and absorb some during the night, but that should not be noticeable. Or much of an issue even if noticed.

I am fairly certain such a mineral is possible, but I doubt it would occur naturally in significant quantity or be chemically stable.

Simple phosphorencence might be better mountain effect.

Alternately you could have the ground release gas that has chemiluminescence in air during the night. So the trigger would probably be the temperature changes.


Silverbark trees, or whatever you would like to term them.

In localized colonies, you have certain night insects/moths/what have you that are attracted to light. To take advantage of this, trees have evolved to be able to store sunlight during the day, and at night they release this stored light through the center of the flowers, creating small spotlight effects.

This light, while not as bright as pure sunlight (in reality however bright you need it to be) shines forth like dozens of nightlights from each plant, attracting the insects needed to promote pollination and the like.

If you need a period of dark, however limited, you can have the charge run down, and in any case since it is localized and not as elevated as a sky light source would be, the sky can remain dark as needed.


How about some kind of Aurora? Maybe there's a black hole nearby that bends light funny and gives the planet a permanent Aurora? or a brown dwarf? For the level of light that might be the best bet, though how it's 'powered' might be up for grabs.

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    $\begingroup$ I want it localized and periodical. The borealis can be viewed even during the day. $\endgroup$ – MikhailTal Jan 28 '15 at 14:26
  • $\begingroup$ @MikhailTal Periodical is fairly easy, it could depend on seasons (where things are in relation to each other, localized is more difficult. how local? $\endgroup$ – bowlturner Jan 28 '15 at 14:28
  • $\begingroup$ You can get localized aurora if there is a magnetic anomaly that bend the magnetic field and causes the radiation belts to hit the atmosphere. Although I think this would probably happen during the day? $\endgroup$ – Ville Niemi Jan 29 '15 at 7:37

How about a universe that isn't expanding in the same way as ours or a star system that moves so rapidly through space so that it catches up with light coming in the opposite direction. (this is based on the idea that the night sky would be completely lit by starlight in all directions if the universe wasn't expanding so rapidly that far away star light never reaches us.) with a rotating planet moving at this speed different hemispheres would be lit each night depending on the speed of the rotation. In a non expanding universe the entire sky would be constantly lit at night anywhere on the planet but daytime would look the same. Maybe if there were a huge amount of celestial masses that block out (eclipse) the star light then it may become localised.

I may have slightly omitted the 'local influence' portion of the question but there you are.

Pretty far fetched but I gave it a go.


How about something like a Dyson sphere encompassing the star and the planet? This could be seen as a bit of an "the ancients built it" McGuffin, but physically plausible.

This is also reminiscent of the planet Krikkit in the HHGTTG trilogy.

You specified a spherical planet, but I am also reminded of how Fafhrd and the Gray Mouser speculated, in Trapped in the Sea of Stars (which can be found in the collection Swords and Ice Magic), that Nehwon was on the inside of a sphere and the stars were actually sunlight shining through large waterspouts on the opposite side. Their philosophical musings while aboard their ship are worth a read.


The Earth has a fairly transparent atmosphere for light in the visual range; if the atmosphere of your planet contained elements that reflect or refract light, the atmosphere itself would transfer light from the 'bright' side of the planet to the 'dark' side. Ice high in the atmosphere can have this effect, as can methane and a number of other chemicals. On Earth, Noctilucent clouds can cause this phenomenon, though it's fairly rare. Lower clouds may assist light pollution from cities, but are too low in the sky to direct light from the sun.

Be careful, though - chances are that a lot of light on the dark side of a planet would cause a considerable amount of heat, too.


In real life, I recall being amazed at the brightness of the night on more than one occasion, due to low-lying clouds reflecting normal city lighting. I don't know if the rare event is due to some special nature of the cloud layer, such as icy crystals which doesn't normally happen in this area. But that's an idea that can be exaggerated.


Light from Lava Flows reflected off a persistent Cloud Layer.

A particular mountain formation near an ocean could create a micro-climate, inducing a continuous thin cloud layer above the city, perhaps even at certain times of the day/night due to the natural onshore/offshore wind cycle. (This actually occurs at certain locations in the Andes - google 'Rain Shadow')

If the mountain was the result of an active 'Hawaiian' style volcano, it could have surface lava emitting large amounts of heat and light that last for centuries.

If, at night time, the cloud layer were to freeze and crystalize, the light from the lava could reflect off the suspended ice layer and back down to the city below.

Alternative : The city was founded inside the cloud layer, and the cloud layer is wandering, requiring the city to move.

You can vary the weather / volcanic activity to change intensity or add impurities to the clouds / lava to change colours.

Good luck!


Think bioluminescence. Maybe there's an enormous cloud of--what? gnats? bats? birds? bacteria, even?--that swarms to a particular part of the sky every evening. Or perhaps it's always there, but bioluminesces when it's feeding, or trying to attract prey or mates.



  • $\begingroup$ This sounds like the outline of an answer. Can you develop this idea more? We're not really looking for short "you could try this" speculative answers but something a little more thorough. Thanks. $\endgroup$ – Monica Cellio Feb 1 '15 at 4:13

Two things come to mind:

1) Put your solar system in a globular cluster of stars. These will provide a constant and fairly even illumination.

2) If you want cyclical bright nights, you could make the moon bigger and make it more white - a greater albedo. The whiteness could come from clouds in the moon. Having said that, a problem with a big moon might be huge tidal forces.

I believe that our moon's regolith is quite a dark grey, but the moon still looks bright against the black of space.


protected by a CVn Feb 1 '15 at 13:42


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