What S_J said is dead right, but here's a diagram anyway because I'd already drawn it.
So, the spin of the coin generates centripetal force, which works much the same as gravity, in this case, sticking the ocean, the atmosphere, the people, fish and everything else to the inside edge of the coin. To blatantly steal an analogy from Iain M Banks' "Consider Phlebas": Imagine that you have a bucket of water with a model boat floating on the surface. Now pick up the bucket by the handle and, holding it at arm's length, start to spin it over your head and back down again. As long as you keep spinning it really fast, the water will never fall out of the bucket, and the boat will not sink, even when the bucket is upside down.
Note that the orbit I've drawn in there could be around Earth or around the sun or even around the moon. Doesn't matter, as long as the sunlight only ever comes in through the bottom of the ocean as shown in the picture. This is because the ocean is what filters out all the harmful radiation.
Note also that my diagram does not show the two circular walls that turn the "wedding ring" I've drawn into a "coin". (If you can't get your head around that, think about what you'd need to add to a wedding ring to turn it into a hollow "coin" shape.) These are the two faces I've been referring to as "heads" and "tails", and they are not transparent. They have two main functions:
1- They keep the atmosphere in.
2- The keep harmful cosmic radiation out. Cosmic radiation comes from all directions, not just from the direction of the sun, so the ocean won't block all of it (unless you are in a submarine.)
Your airlocks and space-ship docking would be on the haids and tails faces.
The dimensions of the coin are beyond my mathematical ken, but you're probably looking at a minimum diameter of about a thousand Ks, and a maximum defined purely by the strength of the materials you are building from. Width-wise, it depends largely on the size of Ceres after you've strip-mined and melted it. Probably in the 200-500Ks range.
You might find that you can have a breathable atmosphere sticking to the ocean in much the same way that the ocean sticks to the coin, but that the centre of the coin, around Ceres, is vacuum (or something close to it.)
Oh, and you don't actually need Ceres in the middle there, by the way. You could take it out if you wanted.
Finally, imagine yourself on Narf's boat. Think about where the sunlight is coming from, and how your surroundings would look. Assuming the coin spins once every 24 hours, where will the light be coming from in 12 hours' time?
Re: OT: Ceres more interesting than previously tho
Hybrid Mode
