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02-21-2018, 02:38 PM   #11
Agemegos

Join Date: May 2005
Location: Oz
Re: Weather in a Dysonish sphere

Quote:
 Originally Posted by Dalillama I was envisioning zero G except where the rocks or globules are big enough to have gravity.
Then you are overlooking the gravity of the atmosphere. The gravity of the shell is zero inside the shell, but even if the 1.25 bar of breathemix is magically prevented from self-gravitating towards the centre its mass is about 1.25 × 0.029 kg/mol × 44.5 mol/m^3 × 4π/3 × (3.65 × 10^13 m)^3 = 3.29 × 10^41 kg = 1.6 × 10^11 solar masses. Assuming standard temperature and pressure throughout.

Surface gravity of the uniform sphere of breathemix would be about 16.5 × 10^4 m/s^2 = 1 682 gees.

Last edited by Agemegos; 02-21-2018 at 03:22 PM.

02-21-2018, 02:57 PM   #12
Anaraxes

Join Date: Sep 2007
Re: Weather in a Dysonish sphere

Quote:
 Originally Posted by Anthony we actually have a supermassive black hole
Well, at least then we don't have to worry about heat radiating away from the outer surface ;)

02-21-2018, 03:23 PM   #13
Agemegos

Join Date: May 2005
Location: Oz
Re: Weather in a Dysonish sphere

Quote:
 Originally Posted by Anaraxes Well, at least then we don't have to worry about heat radiating away from the outer surface ;)
The entire campaign might be set inside the event horizon. The entire shell is.

02-21-2018, 03:32 PM   #14
Anthony

Join Date: Feb 2005
Location: Berkeley, CA
Re: Weather in a Dysonish sphere

Quote:
 Originally Posted by Agemegos The entire campaign might be set inside the event horizon. The entire shell is.
In which case the 'sun' is a naked singularity, and the physics probably don't make sense (but hey, it's a magic setting).
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02-21-2018, 04:34 PM   #15
malloyd

Join Date: Jun 2006
Re: Weather in a Dysonish sphere

Quote:
 Originally Posted by Dalillama I was envisioning zero G except where the rocks or globules are big enough to have gravity. Many of them. The blazing gasballs might have some as well.
Probably not if they are actually blazing - if they were big enough to have much gravity, the oxygen would presumably probably sink down below the butane pretty quickly, any burning still happening is *way* below the cloud tops. Of course the whole system is probably much too recent for that, or the chemistry would have run to equilibrium long ago anyway.

Seriously I don't think this is a sustainable natural system - it's either being maintained by god-like power (in which case the "weather" is whatever said power wants it to be) or a very recent (like thousands of years tops) creation that hasn't quite had enough time to fall apart yet.
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 02-21-2018, 07:20 PM #16 Irish Wolf     Join Date: Jun 2006 Location: Earth, mostly Re: Weather in a Dysonish sphere Which of Niven's settings? The Ringworld spins for effective gravity - its rotational speed of 770 m/s gives it slightly under one Earth gravity. The air is held aboard by massive walls around the edges. The Smoke Ring is in fact a ring of gases, with low gravity throughout, spun off of a gas giant orbiting a binary pair where one star is a yellow dwarf and the other is a neutron star. Maneuvering through the Ring is... tricky; most people never leave the Integral Trees they grew up on. The disc he conceived (but never wrote stories on) is a flat disc like a record, with a star in the middle, and air once again held in place by walls. Gravity would be perpendicular to the plane of the disc, and the area would be in a perpetual twilight (although a day/night cycle could be approximated by "bobbing" the disc "up" and "down"). However, if you decide to solve any issues using magic, make sure you don't also use his magic system. You wouldn't want to be living in, say, the sphere discussed earlier, with things kept from falling into the sun with magic, when the mana fails... __________________ SCIENCE: If you don't make mistakes, you're doing it wrong. If you don't correct your mistakes, you're doing it even more wrong. If you're unable to admit mistakes, you're not doing it at all.
 02-21-2018, 08:23 PM #17 Dalillama     Join Date: Nov 2004 Re: Weather in a Dysonish sphere Yeah, apparently I need a lot more handwaving than I realized. I forgot about several of the effects of spin. Blast. I was hoping for a slightly more clockwork setup, so I didn't have to come up with a reason why it still worked. Oh well. I put some local sapients in, probably they have gods.
02-22-2018, 04:32 AM   #18
Anaraxes

Join Date: Sep 2007
Re: Weather in a Dysonish sphere

Quote:
 Originally Posted by Irish Wolf (although a day/night cycle could be approximated by "bobbing" the disc "up" and "down")
Rather, bob the star up and down through the hole.

The disc was famously mentioned by Larry Niven in his megastructures survey "Bigger Than Worlds", but it's generally attributed to Dan Alderson (including by Niven).

Quote:
 Originally Posted by Larry Niven, "Bigger Than Worlds" What's bigger than a Dyson sphere? Dan Alderson, designer of the Alderson Double Dyson Sphere, now brings you the Alderson Disc. The shape is that of a phonograph record, with a sun situated in the little hole. The radius is about that of the orbit of Mars or Jupiter. Thickness: a few thousand miles. Gravity is uniformly vertical to the surface (freshman physics again) except for edge effects. Engineers do have to worry about edge effects; so we'll build a thousand-mile wall around the inner well to keep the atmosphere from drifting into the sun. The outer edge will take care of itself. This thing is massive. It weighs far more than the sun. We ignore problems of structural strength. Please note that we can inhabit both sides of the structure. The sun will always be on the horizon, unless we bob it, which we do. (This time it is the sun that does the bobbing.) Now it is always dawn, or dusk, or night. The Disc would be a wonderful place to stage a Gothic or a swords-and-sorcery novel. The atmosphere is right, and there are real monsters. Consider: we can occupy only a part of the Disc the right distance from the sun. We might as well share the Disc and the cost of its construction with aliens from hotter or colder climes. Mercurians and Venusians nearer the sun, Martians out toward the rim, aliens from other stars living wherever it suits them best. Over the tens of thousands of years, mutations and adaptations would migrate across the sparsely settled borders. If civilization should fall, things could get eerie and interesting.

Last edited by Anaraxes; 02-22-2018 at 08:48 AM.

02-22-2018, 05:43 AM   #19
RogerBW

Join Date: Sep 2008
Location: near London, UK
Re: Weather in a Dysonish sphere

Quote:
 Originally Posted by Anaraxes The disc was famously mentioned by Larry Niven in his megastructures survey "Bigger Than Worlds", but it's generally attributed ot Dan Alderson (including by Niven).
And was used in fiction by Charlie Stross ("Missile Gap").

 02-22-2018, 08:46 AM #20 Dalillama     Join Date: Nov 2004 Re: Weather in a Dysonish sphere It's a mix of the smoke ring and Howard Taylor's Eina-Oafa, crammed inti the Spelljammer setting. I think releasing a buch of giant air elememtals will solve my problems well enough. As it turns out, none of my players have read any Niven anyway, so it won't invite invidious comparison.

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