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Am 11.11.2012 17:31, schrieb Ed Sweet:
> Here it is with "autotone" in Photoshop.
Yuck. For the twilight, I really do prefer the "raw" version.
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On 11-11-2012 17:30, Ed Sweet wrote:
> This is just POV media, no color correction in Photoshop. Note the yellowing...
>
This is the one I much prefer.
Thomas
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Le 10/11/2012 14:32, Ed Sweet nous fit lire :
> Toroidal planet -- spins so fast it's not a sphere or an ellipsoid, but a torus,
> like "J.P. Boyd's "Moonbow" story in Analog.
>
> Yes, I know that toroidal planets have been shown to be only "meta stable" in
> numerical simulations, and that any perturbation would cause the torus to clump
> up and collapse into a ring of debris or something...so you would need some kind
> of dynamic stabilization to keep it stable...probably not worth the trouble...
>
> but it looks cool...
>
> Modeled entirely in POVRAY.
>
I wonder about the gravity field on the planet itself, just disregarding
the speed of rotation. Seems to me that on the outer radius, the gravity
is strong. On the inner radius, to avoid getting attracted to the sky,
it is weaker and push some constraints between the major & minor radius
(so that the ground is stronger than the sky part).
But on the upper/bottom side(circle) of the torus, it seems that, if the
ground is just along the torus, the direction of a free water surface
would not be parallel to the ground. Wouldn't there be a kind of
desert/cliff making the transition on the small circle between both
region ? would it be some desert or waterfall ?
What about the clouds ? Isn't the atmosphere somehow more extended
inside than outside of the torus ?
What about the difference on the wildlife & flora due to the various
strength of gravity ? (and the cubic/square rule)
Is the daily rotation around the main axis (which might means a 6-month
day if the rotation axis is not aligned with the plane of revolution, or
an ever dim inside-band if they are (well, maybe the shadow cast by the
other side is not large enough to hide the sun, so: umbra, penumbra or
just a bit less light, according to the relative apparent radius of the
sun/minor radius of the planet)
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> I wonder about the gravity field on the planet itself, just disregarding
> the speed of rotation. Seems to me that on the outer radius, the gravity
> is strong. On the inner radius, to avoid getting attracted to the sky,
> it is weaker and push some constraints between the major & minor radius
> (so that the ground is stronger than the sky part).
> But on the upper/bottom side(circle) of the torus, it seems that, if the
> ground is just along the torus, the direction of a free water surface
> would not be parallel to the ground. Wouldn't there be a kind of
> desert/cliff making the transition on the small circle between both
> region ? would it be some desert or waterfall ?
>
> What about the clouds ? Isn't the atmosphere somehow more extended
> inside than outside of the torus ?
> What about the difference on the wildlife & flora due to the various
> strength of gravity ? (and the cubic/square rule)
> Is the daily rotation around the main axis (which might means a 6-month
> day if the rotation axis is not aligned with the plane of revolution, or
> an ever dim inside-band if they are (well, maybe the shadow cast by the
> other side is not large enough to hide the sun, so: umbra, penumbra or
> just a bit less light, according to the relative apparent radius of the
> sun/minor radius of the planet)
The torus is actually "in orbit around itself," with gravity perpendicular to
the surface...though it might be distorted from a torus. It should spin in
about 12 hours or 24 hours or so.
Below is another picture, with some description:
http://www.orionsarm.com/eg-article/49142c044cba7
Below is a further discussion, and also a discussion of how it is not in stable
equilibrium.
http://cosmoquest.org/forum/archive/index.php/t-27790.html
For this picture, I assumed the minor diameter is 4000 km, and the major
diameter is 100,000 km.
It would be built artificially...though heaven only knows who would have the
technology to build something like this, and why anyone would try since it's not
really stable...
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>
> Below is another picture, with some description:
>
> http://www.orionsarm.com/eg-article/49142c044cba7
>
As soon as I saw this picture (I think by Steve Bowers), and remembered reading
J. P. Boyd's Moonbow story (Analog, 1980 or so)...decided that it would not be
that hard to model in POVRAY...
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Am 12.11.2012 19:50, schrieb Le_Forgeron:
> But on the upper/bottom side(circle) of the torus, it seems that, if the
> ground is just along the torus, the direction of a free water surface
> would not be parallel to the ground. Wouldn't there be a kind of
> desert/cliff making the transition on the small circle between both
> region ? would it be some desert or waterfall ?
Of course the gound itself, being subject to the same gravitational
effcts, would settle in a non-perfect toroidal shape. (Similar to how
the earth's shape is not spherical, due to the gravitational forces at
the equator being partially offset by centrifugal forces.)
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On 13/11/2012 4:04 AM, clipka wrote:
> Am 12.11.2012 19:50, schrieb Le_Forgeron:
>
>> But on the upper/bottom side(circle) of the torus, it seems that, if the
>> ground is just along the torus, the direction of a free water surface
>> would not be parallel to the ground. Wouldn't there be a kind of
>> desert/cliff making the transition on the small circle between both
>> region ? would it be some desert or waterfall ?
>
> Of course the gound itself, being subject to the same gravitational
> effcts, would settle in a non-perfect toroidal shape. (Similar to how
> the earth's shape is not spherical, due to the gravitational forces at
> the equator being partially offset by centrifugal forces.)
>
I did some quick calculations and knowing that the centripetal force is
equal to minus the angular velocity squared times the radius times the
mass (F = -W^2*r*m).
If the torus was revolving around its centre once in 24 hours. On the
inner surface the force would be about 0.508g and on the outside surface
0.529g. If the period was 12 hours the forces would be 2.03g and 2.116g
respectively. Note the sleight of hand going from force to acceleration ;-)
This is not a stable configuration. If there was a star in the centre of
the torus. Any slight movement of the torus to the centre would be
magnified by the closer part being attracted to the star more than the
part that is further away. Starting a wobble that would end up looking
like a hula hoop.
Never the less a nice concept and image.
--
Regards
Stephen
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Stephen <mca### [at] aol com> wrote:
> This is not a stable configuration. If there was a star in the centre of
> the torus. Any slight movement of the torus to the centre would be
> magnified by the closer part being attracted to the star more than the
> part that is further away. Starting a wobble that would end up looking
> like a hula hoop.
Not a wobble, if it encircled a star there would be no orbital motion - an
outright crash! This is the scenario overlooked by Niven in Ringworld, which he
later retconned with the rim stabilising thrusters.
However, I do not believe the present artifact is supposed to encircle a star,
or spin like a ringworld (at least not enough to generate significant
centrifugal forces). I like the idea that it is planet-scaled, generating
gravity by virtue of its own mass. It is difficult to see how it could form
naturally of course...
Bill
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Le 13/11/2012 07:04, Stephen a écrit :
> This is not a stable configuration. If there was a star in the centre of
> the torus.
I do not expect a star at the center. Rather far far away.
(a star at the center gives us back to a Dyson sphere, or belt in such
case)
But remains the question of coincidence of planes for rotation &
revolution, and the impact on day-light on some part of the surface.
Any slight movement of the torus to the centre would be
> magnified by the closer part being attracted to the star more than the
> part that is further away. Starting a wobble that would end up looking
> like a hula hoop.
If the star has any significant difference of influence on the near &
far part of the torus, it will crumble the torus fast.
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Le 13/11/2012 07:04, Stephen a écrit :
>
> I did some quick calculations and knowing that the centripetal force is
> equal to minus the angular velocity squared times the radius times the
> mass (F = -W^2*r*m).
> If the torus was revolving around its centre once in 24 hours. On the
> inner surface the force would be about 0.508g and on the outside surface
> 0.529g. If the period was 12 hours the forces would be 2.03g and 2.116g
> respectively. Note the sleight of hand going from force to acceleration ;-)
There is more than just a delta in the centripetal force. (on the outer
circle, it is opposite direction of gravity (like on earth); on the
inner circle, it should be the same direction as local gravity (but the
local gravity is diminished due to the point being between "two massive
parts"
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