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Thread: STTNG Bad Astronomy?

  1. #1
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    Just sat down and watched an episode of Star Trek The Next Generation. The episode was "Relics". In it, the crew comes upon what is termed a Dyson's Sphere. This sphere is constructed completely around a star at the distance the Earth is from the sun. Inhabitants can then live on the inside skin of the sphere. Interesting.

    I checked the web, There was actually a Freeman Dyson. But, given the task, and assuming that we could accomplish such an engineering feat, would something like this work? Or is it a baaad case of Bad Astronomy? I'm jsut thinking about the ramifications of the solar wind against the inside of the sphere. It could turn into the universes's largest microwave oven!!

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    Bad astronomy in Star Trek, never! [img]/phpBB/images/smiles/icon_eek.gif[/img] [img]/phpBB/images/smiles/icon_wink.gif[/img]
    I guess a sphere would be a bit impractical since all that energy would be enclosed. I think a thin disc ala Larry Nivens 'Ringworld' & also the orbitals in Ian M Banks Culture novels, would be more practical from that point. Of course it would still need stabilising thrusters of some sort to keep it in orbit around the sun (net gravity in centre being zero).
    I enjoyed that episode (Scottie instructing the holodeck to recreate the bridge of the original Enterprise.. 'NCC1701 & no bloody A B C or D' or something like that [img]/phpBB/images/smiles/icon_smile.gif[/img]

  3. #3
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    On 2002-02-18 07:31, trusty wrote:
    I checked the web, There was actually a Freeman Dyson.
    There's a few web references to Dyson Spheres too. Here's a Dyson Sphere FAQ that seems pretty reasonable, although I didn't read all of it. It says:

    The original proposal simply assumed there would be enough solar collectors around the star to absorb the starlight, not that they would form a continuous shell. Rather, the shell would consist of independently orbiting structures, around a million kilometres thick and containing more than 1e5 objects. But various science fiction authors seem to have misinterpreted the concept to mean a solid shell enclosing the star, usually having an inhabitable surface on the inside, and this idea was so compelling that it has been the main use of the term in science fiction. The earliest appearance of this version seems to be Robert Silverberg's novel Across a Billion Years.

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    Wouldn't be able to live on the inside surface (not without those imaginary "gravity boots" anyway). Gravity is balanced anywhere inside of a sphere; add a sun in the middle and the gravity toward the center and opposite side is now greater than what's under your feet, so you float right off toward the sun. What a cruel way to die after investing such enormous resources to build the thing.

    <font size=-1>[ This Message was edited by: Mnemonia on 2002-02-18 08:14 ]</font>

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    On 2002-02-18 08:13, Mnemonia wrote:
    the gravity toward the center and opposite side is now greater than what's under your feet, so you float right off toward the sun.
    Unless you, and what you are standing on, is in orbit. Then you'd just orbit together. You could fly.

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    You spin the puppy... (Okay, it's made of Krell Steel, or Scritch, or Garble-lepton Buzzword matter...) At the equator, you have "gravity," which fades in strength the farther north or south you go...

    I was disappointed in Star Trek for introducing something so vastly promising -- let's explore it and find all the new civilizations! -- and then just destroying it. Feh. Cowards.

    (Credit to Deep Space 9 for introducing the first actual *CHANGE* in the Star Trek cosmos!)

    Silas

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    On 2002-02-18 07:58, GrapesOfWrath wrote:
    On 2002-02-18 07:31, trusty wrote:
    I checked the web, There was actually a Freeman Dyson.
    There's a few web references to Dyson Spheres too. Here's a Dyson Sphere FAQ that seems pretty reasonable, although I didn't read all of it. It says:

    The original proposal simply assumed there would be enough solar collectors around the star to absorb the starlight, not that they would form a continuous shell. Rather, the shell would consist of independently orbiting structures, around a million kilometres thick and containing more than 1e5 objects. But various science fiction authors seem to have misinterpreted the concept to mean a solid shell enclosing the star, usually having an inhabitable surface on the inside, and this idea was so compelling that it has been the main use of the term in science fiction. The earliest appearance of this version seems to be Robert Silverberg's novel Across a Billion Years.
    Here's a site which explains the Dyson sphere from a Star Trek perspective.

    http://www.ditl.org/ships/heddyson.htm

    It even makes reference to Freeman Dyson.

    Yeah, I'm a trekkie. Why do you ask? [img]/phpBB/images/smiles/icon_lol.gif[/img]




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    I guess a sphere would be a bit impractical since all that energy would be enclosed.
    Not really.
    1) the energy per unit area is the same as that for a planet at the same distance. In other words, there may be a lot of energy, but there is a lot of area as well.

    2) The whole point of a Dyson Sphere is that when a civilization reaches the point where it needs the entire energy output of a star, then the best way to harness the star's energy is to build a sphere around it.

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    1) true, well at least it would be the same as at a point 90 degrees to the incident rays on a planet ie one season all the time.. oh hang on theyd have sun blocking panels or something [img]/phpBB/images/smiles/icon_smile.gif[/img]

    2) Yes, & i guess such a technologically advanced builder would have a means of getting rid of any excess energy anyway.

    I'll shut up & get me coat [img]/phpBB/images/smiles/icon_smile.gif[/img]

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    Maybe the people should live on the outside of the sphere. Then the sun's gravity would hold them to the surface. Since the sun has about 330,000 time the mass of the earth, the sphere would have a surface area 330,000 times that of the earth if you want the same gravitational pull.

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    On 2002-02-19 00:00, Chuck wrote:
    Maybe the people should live on the outside of the sphere. Then the sun's gravity would hold them to the surface. Since the sun has about 330,000 time the mass of the earth, the sphere would have a surface area 330,000 times that of the earth if you want the same gravitational pull.
    That would make it, what, five times the radius of the Sun now? You're going to have some hotfoots.

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    They could use air conditioners. They'd have plenty of solar power to run things.

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    On 2002-02-19 08:24, Chuck wrote:
    They could use air conditioners. They'd have plenty of solar power to run things.
    Lol!
    btw i'm now crosseyed from looking at your website [img]/phpBB/images/smiles/icon_smile.gif[/img]

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    They'd also need lights. If they're living on the outside of a solid sphere enclosing the sun, they're certainly not getting any direct sunlight!

    BTW -- what would be the effect of the sun's gravity on such a sphere? Being that close, the gravity'd be pretty strong, wouldn't it?

    We've discussed hollow spheres and gravity before, but that was within the context of the sphere's influence on an object inside it . . . what about the internal object's influence on the sphere itself?

    Sometimes you win, sometimes you learn

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    On 2002-02-19 08:46, SeanF wrote:
    BTW -- what would be the effect of the sun's gravity on such a sphere? Being that close, the gravity'd be pretty strong, wouldn't it?
    One g

    Strong enough.

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    BTW -- what would be the effect of the sun's gravity on such a sphere? Being that close, the gravity'd be pretty strong, wouldn't it?
    The relationship is symetrical. The sphere has no effect on the star and the star has no effecton the sphere. If an asteroid hits the sphere and gives it a nudge, eventually they will collide. If the star has an asymetric CME and starts drifting, eventually they will collide.
    In other words, without active stabilization, eventually they will collide.

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    <font size=-1>[ This Message was edited by: Kaptain K on 2002-02-19 11:49 ]</font>

  17. #17
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    On 2002-02-19 11:48, Kaptain K wrote:
    The sphere has no effect on the star and the star has no effecton the sphere.
    Yeah, in the same way that the earth has no effect on an apple hanging on a tree.

    Since the gravity would be one g, the sunward force would be the same as on that apple. Or the roof of the superdome. Hey, that's what it would be--a gigantic dome held up by itself. The spans would be pretty flat, too.

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    Yikes!

    The Sun's gravity is not one g at the Earth's distance! The acceleration due to gravity is equal to G x m / r^2, where g = Newton's constant, m = mass and r = distance. For the Earth, that comes to the familiar 9.8 meters/second^2 at the surface.

    Putting in the Sun's mass and distance, I get 0.006 m/s^2, or 0.0006 gravities at the surface of the Dyson sphere.


    <font size=-1>[ This Message was edited by: The Bad Astronomer on 2002-02-19 13:46 ]</font>

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    Sorry, BA, didn't mean to wake you up!

    We were discussing Chuck's hypothetical Dyson sphere with only 300,000 times the surface area of the Earth. It's radius is only five solar radii, I think.

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    Ah, I missed that reference. To get one gravity, I get a sphere with radius = 4.5 million kilometers, roughly 6.5 times the Sun's radius. That's a surface area of 6.4 x 10^13 square kilometers, compared to 1.3 x 10^8 for the Earth, a factor of roughly 500,000 times the Earth's surface area.

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    Okay, either my numbers are wrong or my math is. Sol's got a mass of 332946 Earth masses . . . square root of that is about 577.015, so at 577.015 times the distance, we'd have the same gravity, right?

    Earth diameter = 12756Km, Sun diameter = 1,392,000Km, ratio = 1/109.1251, 577.015/109.1251 = approx. 5.29 solar radii.

    I'm closer to Grapes' numbers than to the BA's, and that don't seem right! [img]/phpBB/images/smiles/icon_wink.gif[/img]


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    Um. I just redid the calculation a different way and now get a distance of 3.7 million kilometers, or 5.3 solar radii. I have no idea what I did before, but it was wrong.

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    Lighting would not be a problem. Drill a hole anywhere.

    How hot would it be? If it's 5.3 solar radii from the sun it's surface area would be about 28 times that of the sun. Since it traps all of the sun's output it would eventually radiate at 1/28 the sun's surface temperature in Kelvins, right?

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    The calculation was easy. Since the gravitational pull decreases with the square of the distance and the area of the sphere increases with the square of the distance the two cancel out and the surface area is directly proportional to the mass of the star.

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    On 2002-02-19 17:09, Chuck wrote:
    How hot would it be? If it's 5.3 solar radii from the sun it's surface area would be about 28 times that of the sun. Since it traps all of the sun's output it would eventually radiate at 1/28 the sun's surface temperature in Kelvins, right?
    You mix temperature and energy and we talk about radiation.
    You'll have 1/28th of the energy flow per area unit. But there is not a linear relation between
    temperature and energy radiated. It is actually proportional to the fourth power of the temperature, that means, if you double the temperatur (in Kelvin) of a body, it radiates 16 times more energy. So, to get rid of 1/28 of the energy per area unit of the sun, tghe body must have a temperatur of 1/2.3 (~2/5th)
    of the suns temperature.
    I hope I'm not badly wrong with this.
    Harald

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    On 2002-02-20 02:52, kucharek wrote:
    You mix temperature and energy and we talk about radiation.
    Worse, there is a zone above the Sun's "surface" that is many times hotter.

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    [quote]
    On 2002-02-20 05:22, GrapesOfWrath wrote:
    Worse, there is a zone above the Sun's "surface" that is many times hotter.
    The corona is so rarified, do you think it would make a difference? Sure, its 1,000,000K but it's also almost vacuum. Is there that much energy?

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    On 2002-02-20 10:11, Wiley wrote:
    The corona is so rarified, do you think it would make a difference? Sure, its 1,000,000K but it's also almost vacuum. Is there that much energy?
    No, I'm sure it doesn't, I just meant to point out that you have to be careful in extrapolating temperatures by radius. Well, more than careful.

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    Something just occured to me. In the contaxt of the ST:TNG episode "Relics" version of the sphere. This thread has been assuming that there were people in it. If I remember the episode the crew found no signs if life. So, is it reasonable to say maybe the sphere was not such a great success after all ? [img]/phpBB/images/smiles/icon_smile.gif[/img]

    Darasen

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    On 2002-02-21 23:56, Darasen wrote:
    Something just occured to me. In the contaxt of the ST:TNG episode "Relics" version of the sphere. This thread has been assuming that there were people in it. If I remember the episode the crew found no signs if life. So, is it reasonable to say maybe the sphere was not such a great success after all ? [img]/phpBB/images/smiles/icon_smile.gif[/img]

    Darasen
    It was quite a success, until the star became unstable. Then it had to be abandoned. (although they never explained why)



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