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How far can you see through an atmosphere like the one we have on Earth? The protagonist inhabits a huge world, like the inside of a sphere, a Dyson-sphere, with an approximate circumference defined by the circle of Earth’s orbit. The world is magical and thus atmosphere is retained on the inside of the sphere, uninhibited by the laws of physics. In fact, a breathable atmosphere is available in up to 30 kilometers altitude. But as the surface curves upwards (albeit very slightly) instead of downwards as on Earth, it would be possible to see farther than here, if the atmosphere does not obscure the view. Theoretically, there could be a lot of air between two points of observation! (Note that this particular world is divided into "smaller" segments by a form of curtain-like dividers, but some of the segments are much larger than, say, the surface of our own planet.) I’m thinking about the way water filters out more and more light as the mass of water between light source and place of observation grows. Does that same mechanism affect atmospheric air?

Added explanations in response to comments: The (inner) surface of the sphere is mostly uninhabited wastelands, barren rock with traces of water and lichen, and with a thin layer of breathable atmosphere. Inhabited areas consist of "islands", made up by hundreds of segments, divided by "solar curtains" that seem like fog or mist, but actuav´lly philters out sunlight. The central "sun" is covered, but allows for relatively thin stalks to drop towards inhabited segments, like elongated snails eyestalks, so that every segment in practicality has their own sun. There are no moons or stars, but a few other heavenly bodies. Thus one segment may experience day simultaneously with a neigbouring segment experiencing night. Also, weather and climate may vary drastically as a being passes a curtain between segments. All of this is possible because of magic. ("Gods" play an important part here.)

KimotoCat
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  • A PS to my question: Would the answer be different if the area under the atmosphere consists of a huge ocean, again, much larger than the entire surface of our planet, but with some islands and smaller continents. – KimotoCat Nov 01 '18 at 17:32
  • Related: Visibility in a ringworld atmosphere? – Alexander Nov 01 '18 at 17:36
  • Through the atmosphere that we actually have on Earth we can see (with the naked eye) stars up to two thousand light-years away. And you may want to look up aerial perspective. – AlexP Nov 01 '18 at 17:36
  • See also Extinction_(astronomy) – Alexander Nov 01 '18 at 17:44
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    It's going to depend on a lot of variables such as humidity, temperature, and turbulence. Also note that because air scatters blue light, at some point it'll just look like a blue sky. But you'll almost certainly be able to see quite a bit further than on Earth. – Gene Nov 01 '18 at 17:50
  • Another concern - Earth's atmosphere is thinning with altitude. Its equivalent thickness is about 10 km. If in this scenario we have a uniform 1 atm pressure up to 30 km, and then vacuum, the equivalent thickness is 3 times more than on Earth. – Alexander Nov 01 '18 at 18:02
  • Are there any contaminants in the atmosphere? How does the atmospheric air remain at a constant pressure all the way up to 30 km? Will there be a constant aroura everywhere due to the solar wind? What does the Atmosphere-Space boundary look like? What frequencies of light are you talking about, all visible? – Mathaddict Nov 01 '18 at 18:57
  • Note also that independently from the question of whether light can reach your eye, your ability to resolve small objects at long distances is limited by very fundamental optic considerations (although it is wavelength dependent) – Alexis Nov 06 '18 at 16:32
  • @KimotoCat "some of the segments are much larger than, say, the surface of our own planet." Definitely. That sphere is STAGGERINGLY vast. The surface area is on the order of 10^17 km^2. You can fit 100 MILLION EARTHS on that thing. It is functionally infinite for any pre-space age society. – Mark_Anderson Nov 09 '18 at 17:48
  • Also see https://worldbuilding.stackexchange.com/a/45097/21222. – The Square-Cube Law Nov 11 '18 at 09:01
  • This is certainly a duplicate, but bear in mind, you can't "see clearly" much beyond about 5 miles because your eyes can no longer resolve the fine details. It isn't an issue of the atmosphere, it's an issue of the scanning resolution of your eyes. The larger the object you're trying to see, the further away you can see it. Therefore, even if this question were not a duplicate, you'd need to specify the exact object (size, shape, color, albedo, etc.) you were trying to see. That might actually make a better question. Let's ask it (and it might be a duplicate). – JBH Nov 11 '18 at 16:59

2 Answers2

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Arguments for not being able to see the whole sphere:

  1. Its size. If we're talking a real sphere here, we'd have a radius of 150 million km. The curvature would be 0.0000427 times of earth's curvature - horizon (as we know it) would be some 58,000 km away instead of 10 km.
  2. Atmospheric scattering, the reason we don't see stars during the day. If your atmosphere is 30 km thick, the effect would be even stronger. Also, we're in a Dyson's Sphere - the sun always shines!
  3. Clouds, dust, mountains and all that stuff blocking your view even more, when you're inside the sphere.

Arguments for being able to see the sphere or parts of it:

  1. The sun shines on the whole sphere, therefore reflects from everything. As the moon is visible during the day sometimes, so should be at least the "sides" of your sphere. Since everything would be much too far away to make out details, you'd get the feeling of sitting a the bottom of a gigantic bowl. The far end of the sphere might be too far way - and blocked by the sun - but at least half the sphere could be visible, possibly more.
  2. The straighter you look up, the less atmosphere could scatter the photons. If you look up at an angle of 45°, light reflected from the "sides" of the sphere would have to travel about 45 km through your atmosphere to reach you. Not that much, a low new moon is visible through roughly similar distances of atmosphere.

tl;dr: I think, your hero would see a "ring" hovering midsky, like a very large halo around the sun. The lower/closer edges of the sphere are obscured by obstacles, clouds and the atmosphere, the far edges by the sunlight, which is way brighter than the sphere's reflection of it.

Erik
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In extremely clean air in Arctic or mountainous areas, the visibility can be up to 160 km (100 miles) where there are large markers such as mountains or high ridges.

https://en.wikipedia.org/wiki/Visibility

Artistic licenses would allow you to extend that quite a bit; perhaps your air is even clearer that the clearest Earth air. But visibility of 1 AU would put you solidly in the realm of being radically different from the real world.

Acccumulation
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