# Day-to-Night observable Sky on a Orbital (non-Niven, small ring) [closed]

I'm assuming a lot of things here, but trying to visualize some characteristics regardless. What would the skyline look like? Day/night, seasonally, etc.

I'm imagining a structure that is a ring, but spins like a coin; slowly traveling around the sun (so much smaller than a Niven ring world that goes all the way around the entire year-path). I'm not settled on the exact size - but I imagine retaining walls, and more surface area than earth. For simplicity, it would be rotating on the z axis, traveling along the x/y axis around it's sun. I could orient/tilt it such that the shadow couldn't possibly hit the other side, but I don't think this would look as "cool".

Would the other inner edge of the ring be visible at all times? Would it be lit up at night? Would you still be able to see stars while your inner side was facing away from the sun? Would atmosphere impact visibility (like it does with mountain ranges sometimes - where it appears hazy during certain weather). Is there ever a point where the ring casts a shadow on itself? If so, what would that look like to observers on either side of the inner edge? How would things look in a landscape that curved up? Would you be able to see other cities, buildings, etc.?

I'm trying to get a better idea of how to showcase this from the viewpoint of characters living on the surface and what they would notice.

Just to clarify some things about the structure

• Smaller ring that rotates & spins
• Still travels an elliptical "yearly" arc around the sun
• Large retaining walls at the sides to block atmosphere from escape.
• Earth like atmosphere
• Physics says first bullet is impossible.
– L.Dutch
Commented Jul 21 at 15:37
• I do not understand what the question is about. "Spinning like a coin" makes me think that the ring rotates around a diameter; at least, this is how spinning coins spin; but on the othe hand, this makes no sense. Why would one build a large ring and then spin it around a diameter instead of spinning it in the plane of the ring? "A diameter of 3.7 million kilometers" is definitely not small; that's ten times the distance from the Earth to the Moon. A "ring that rotates and spins" is . . . very unclear. The two words are synonymous; they mean the same thing. VTC because it needs clarification. Commented Jul 21 at 16:58
• @AlexP I acknowledge the confusion. Hard to describe in words what I'm referring to. Yes, centrifugal spinning like a top/frisbee would still be happening (rotational), then also flipping (like a coin on a table). On top of this it would be going around a sun (like a normal planet would). I edited out the numbers I just pulled those from an orbital reference (not important). Commented Jul 21 at 19:07
• Oh, the famous rotation around two axes at once. I for one would not want to argue with Euler's rotation theorem. Quarrels with basic geometry have very low chances of success. Commented Jul 21 at 19:46

Would the other inner edge of the ring be visible at all times?

Yes, the other inner edge of the ring would be visible at all times, but it might look hazy due to the atmosphere, similar to how distant mountains appear.

Would it be lit up at night?

The opposite side might still catch some residual light from the sun, giving it a faint glow at night, like twilight.

Would you still be able to see stars while your inner side was facing away from the sun?

Well, when your side is turned away from the sun, stars would be visible, assuming the weather is clear.

Would atmosphere impact visibility (like it does with mountain ranges sometimes - where it appears hazy during certain weather)?

Sure the atmosphere would impact visibility. The opposite inner edge of the ring might look hazy, especially on cloudy or foggy days, similar to distant mountains.

Is there ever a point where the ring casts a shadow on itself? If so, what would that look like to observers on either side of the inner edge?

Yes, the ring can cast shadows on itself. During sunrise and sunset, you would see moving shadow lines, creating dramatic contrasts between light and dark areas. This would be a striking visual effect for observers on both sides of the inner edge.

• Do you you think you'd experience a shadow at some point akin to an eclipse at high noon? Commented Jul 21 at 19:10

What I understand from your description it's a Banks orbital. It's a structure much smaller than a ringworld and does not encircle the whole star. It spins like a wheel, not a coin, while at the same time orbits its star like a planet. This allows centrifugal force to mimic gravity, just like aboard a rotating space station. If large enough, its simulated gravity can even hold an atmosphere and will not need a "roof" to hold the atmosphere, just the retaining walls. This will allow its inhabitants to take-off into space and land back.

Here are some facts about the Banks orbital:

• It rotates like a wheel. The inhabitants and everything on the inside, including the atmosphere will be held on the inner surface by spin-gravity. Spinning it like a coin will not create a uniform spin-gravity.

• It can be set an any axial tilt you want, just like a planet. As it orbits its star, this axial tilt will create seasonal changes.

• The surface is cylindrical, not spherical, so all parts of the megastructure will experience the same season at any time. Remember - No north and south hemisphere, so the sun's angle will be the same anywhere.

• The star always shines on the inside (habitable) of the far side and the outside of the near side (the outer structure). Depending on the hour of the day, at a fixed location we will see a "light arch" where the lit parts appear in the sky. The light arch progresses and recedes relative to a fixed observer. It may be partially visible during the day just as we often see the moon during the day. We will not see dark parts during the day, due to the sky's raleigh scattering. However, at night the dark parts will be noticeable, because they obstruct the starlight.

• A banks orbital, having an axial tilt, undergoes seasonal changes. However, during an equinox, observers will see the opposite side of the orbital obstructing some or all of the sun light, depending on its width.

• Unlike the lack of North and South hemisphere as an ordinary planet has, the areas bordering the Northern and Southern retaining walls will be in shade during their "winter": At half of the year the Northern retaining wall will cast a shadow on a wide area, while at the other half of the year the Southern retaining wall will cast a shadow. This is due to the axial tilt. The length of the shadow progresses and recedes with the seasons. This may create a unique ecosystem at the "rims" of the orbitral. It will be interesting to study this effect and whether the rayleigh scattering from the atmosphere will provide some diffuse light enough for photosynthesis. The seasonal change will be strong enough to cause plants to respond to seasonal changes and trigger seasonal animal migration.

All I could answer is that for certain each side will eclipse the other fully each day at noon on the side getting sunlight. I get the coin flip (to provide for day/night). Each side’s shadow will mostly cover the other side during daily eclipse, since both sides are the same size. My best guess is that Yes; stars will be visible for the side that’s opposite to the sun, specially during the moments of full eclipse at midnight. However, during the rest of the night the other side would cast a very bright light that will obscure most of the details of the sky. Things like the Milky Way line would definitely be too faint to see against the brightness of the daytime side of the ring. It would be like a full moon but even brighter. Just imagine if the moon was as long as the entire sky. You would still be able to see stars but not as many.

Also, the eclipses will possibly look either mostly completely dark if no atmosphere escapes the sides of the ring system due to the edge walls. So it wouldn’t have a red effect that the moon gets due to the sun’s light being filtered and bent by the earth’s atmosphere. That’s as much I can think of. Hope it helps. Ask if you got any questions.