There are many reasons for the night to not be dark. Even after you eliminating, fires, volcanoes or your porch light you will not have a truly dark experience. If the moon happens to be above the horizon you will be again be bathed in the light from our sun reflected off of the moon. Moonlight can be bright enough to see objects and your surroundings with no problem, though colors are reduced to drab shades of grey. You can see your shadow and moonlight prevents most clear nights from being dark. Take the moon away. Would you then have a dark night? As dark as the closet? Actually no, quite far from it. Turning out the lights and picking a moonless night ends the immediate glare but as your eyes become accustom to the dark, previously unnoticed sources of illumination become apparent. Lights from a nearby town or city light up the sky, especially if there are clouds passing over the light source. Light from cities reflect off clouds, moisture and dust in the atmosphere and can provide illumination nearly as bright as the moon. This sky light can be bright enough to overwhelm the light from all but the brightest stars.
Get away from the cities, towns, airports shopping malls and highways and you will leave the sky reflected light behind and again presumably set the stage for a true dark night. However, even after you have escaped from civilization and are out on a clear moonless night, especially in the summer, you will realize this is still no dark closet. The sky can still be veiled with a hazy diffuse light. This is called air glow. The molecules of air in the thin upper atmosphere of the Earth, after a day of bombardment from the ultraviolet portion of sunlight, will absorb this radiation and in doing so loose some electrons to become ionized. This is not a stable condition and as the night proceeds these gases calm down, recapture their lost electrons and in the process emit feeble light. This sky glow can also overwhelm the light of dim stars and provide enough ground illumination to see clearly by. A more energetic version of this light show is the Aura Borealis or Northern Lights. Eruptions in localized areas of the sun's surface, called flares spew clouds of high energy particles and radiation that escape the sun's gravity. A continuously flow of much lower energy level particles also occurs called the solar wind. This energetic material is captured in the Earth's magnetic field as it travels away from the sun and is guided to the poles where it streams down into the upper atmosphere and collides with the Oxygen, Nitrogen and other molecules of which the air is composed. This bombardment provides a much more sudden and violent shock to the air molecules than the ultraviolet bath of the noon day sun, particularly when a flare on the sun directs this material at the earth. These shocked air molecules also lose electrons but more more of them and when the gas calms down recapture of the lost cloud of negative electrons provides a more significant burst of light. The Aura are mostly green but can also be blue, yellow and red. A sky charged with high energy particles will emit light nearly as bright or brighter than a full moon.
So eventually you find yourself in the middle of a desert in the southwest, hundreds of miles from civilization's lights and south of all but the highest energy and least frequent low latitude aural displays. You are there preferably there in the middle of the winter when the sun's light is indirect enough to do little energizing of the atmosphere. Now you expect a dark night right? Well not so quick. When the dust settles you look around and still see the ground, your hand in front of your face and very likely your shadow. This is because all light has not been eliminated. What remains is the light from the hundreds of thousands of points of light in the sky high above and the irregular milky white band of diffuse light that stretches from horizon to horizon all of which make up our Milky Way galaxy. The light from the suns in our galaxy are shining brightly through trillions of miles of space to light our dark night. The sum of all these candles in the dark is a light that you can walk by and see nearby surroundings. A "bright, starlit night" is exactly that, bright, and this brightness is due solely to the star light shining down from all directions above.
But this is a dark sky isn't it? Even though it is covered by tiny points of light, none amounting to more than a twinkling point. Even the planets Mercury, Venus, Mars, Jupiter and Saturn, though they outshine the stars, still do not exhibit more than the point source of light unless you observe them through the magnification of binoculars or a telescope. This is our dark night. But what if it wasn't like this.
What if we lived on a planet orbiting a star that was not isolated like our sun but a member of a group of suns all born from the same nebula of gas an dust. If we lived on a planet where our sun was a member of a cluster such as this one that I photographed through my telescope, the only dark we would know would be what we could find in a closet, closed room or cave under ground. On our planet orbiting a cluster sun, there would be hundreds or thousands of suns in our sky all farther away than our sun but close enough to have a visible disk. Some might be reddish or yellow, bluish or orange. Many shining brightly enough to be painful to look at directly and all shining their light down continuously from all directions in the sky. Sources of light to fill the sky much brighter than a full moon all the time. The only variance during the rotation of the planet would be when the sun that we orbit is above the horizon to join the many other smaller suns. No day and night but only bright and brighter. On a world orbiting a cluster sun the inhabitants would not know what night was, dark yes, but closet dark, not outside walking around in the dark. Outside dark would not exist and the term "night" would have no meaning or at least not the same as we give it.
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