I was not thinking of a Niven ring; I wasn't think the star would be in the middle of the torus. I was, in fact, thinking the torus orbited a normal star, much as a more spheroidal planet would.gestaltist wrote:Hard to say without more data. Where is the light source/star placed? In the middle of the torus? Or does the torus orbit a normal star? Also: which side of the torus is inhabited?eldin raigmore wrote:Leaving aside the gravitational physics of a toroid planet; what would its days and seasons be like?
My idea is that the axis of rotation goes through the center of the donut-hole, and is nearly -- but not quite -- perpendicular to the plane of the planet's orbit.
(Maybe the angle should be about 67.5 degrees, so the axial tilt would be about 22.5 degrees?)
(Maybe the donut-hole's diameter should be the same as the Earth's? And maybe the cross-section of the solid part of the torus, transected by a plane that contains its axis of rotation, should consist of two disks about the same size as such a cross-section of the Earth?)
I was thinking that people would try (and probably succeed) to live pretty much everywhere on the planet where there was any life at all.
The parts of the inner surface of the toroid would have be eclipsed from the sun by the opposite side of the toroid. Some parts would have regular day/night cycles in their "summer" (and "spring" and "autumn"?). At those seasons of the year, when a bit of the inner surface rotated into the eclipse, it would have rotated to be not illuminated by the sun anyway (it would be " on the night side".). But for the other half(? quarter?) of the year, it would be dark all the time; when it was on the "day-side", it would be eclipsed by the other half of the toroid.
I don't know what dimensions a toroid would need to have the same volume/same mass as the Earth.
If the "hole" were much thicker than a cross-section of the "body", there'd be much less of that eclipsing I spoke of above, unless the angle by which the axis of rotation met the plane of orbit were much closer to 90 degrees. (That is, axial tilt much nearer to 0 degrees).
OTOH if the "hole" were much thinner than a cross-section of the "body", there'd be much more of that eclipsing I spoke of above, unless the angle by which the axis of rotation met the plane of orbit were much closer to 90 degrees. (That is, axial tilt approaching 90 degrees.)
I really appreciate all the answers! And I thank everyone who even thought about answering!
I should, particularly, say that elemtilas's stories were excellent!
The thing has to orbit its primary star; it can't just stay in one place a certain distance from it.elemtilas wrote:[Anyone living on the outside aspect of Toroidworld, on the spaceward side, would never know the true nature of the world. Anyone living on the sunward side would have a pretty clear idea: they would be able to see hundreds or thousands of iterations of the Green Worlds. Those living on one of the inner aspects of Everbright would also be able to see the darker stretches of Everdim high overhead.
It is highly likely to rotate, too.
Likely it will rotate several times per orbital revolution.
OTOH maybe a "day" (period of rotation) and a "year" (period of revolution) could be exactly the same length; if that were the case, there'd be a side that was always "sunward" and a side that was always "spaceward". (We would say "the planet is tide-locked to its primary star".)
A "year" would be unlikely to be an integer number of "days" long; but it might, and even if it didn't, it might be close. IMO 365.25 is kinda close to integral.
The number of "days" in a "year" could be quite small, even if non-zero, and as near as I can tell it's likelier to be a whole number if it's small.
For instance, a "year" might be 2, or 3, "days" long.
Or a "year" might be 1.5 "days" long (i.e. a "day" might be 2/3 of a "year").
It's even possible that a "day" would be longer than a "year".
Could that be because the rotation were retrograde relative to the revolution?
Or could the rotation be non-retrograde, but just noticeably slower than the revolution?
If it rotates, it's unlikely that the axis of rotation is perfectly perpendicular to the orbital plane.
There's enough difficulty just thinking about the toroidal shape of the planet, without introducing the addition complexity of figuring out what happens if the axial tilt is more than 45 degrees. So I'd assume the axial tilt is less then 45 degrees (but more than 0 degrees); otherwise there'd be no analogue to "a temperate zone".
If there's axial tilt, the axis probably precesses. It probably takes many "years" to precess; it certainly must take many "days" to precess.
The axis probably also nutates (nods).