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Does Niven ever address the factor-of-two difference in insolation that remains even after he arranges for it to be night half the time?

Date: 2009-01-22 01:32 am (UTC)
From: [identity profile]
What is this factor of two difference in insolation?

Coincidentally, half an hour ago I picked up Fleet of Worlds at the library. I've yet to see a Niven collaborative work I like, and I've seen a good number of Niven works I don't, so I don't have my hopes up... but I'm giving it a chance.

Date: 2009-01-22 04:03 am (UTC)
From: [identity profile]
A sun which is straight overhead is brighter than one that is rising or setting. This means that Ringworld gets, on average, twice as many photons per square meter as Earth does assuming everything else is comparable (sun size, sun distance, and "night" being on average 12 hours out of 24).

We get the factor of two since Ringworld has 2πRw square meters of livable surface and catches ½*2πRw/4πR^2 of its sun's light (the shadow squares get the other half), and Earth has 4πr^2 square meters of livable surface and catches πr^2/4πR^2 of the sun's light.

Date: 2009-01-22 05:49 am (UTC)
From: [identity profile]
The answer to the question you actually asked is I have no idea.

However, the answer to the question "Could Ringworld as presented be sufficiently Earthlike?" is that if you're talking about simple heat balance, it would probably be easy to adjust the optical depth of the ground such that the ringworld gives off enough blackbody heat from its outer side to balance the extra insolation. After all, the Earth is way way thicker than a ringworld and has residual core heat to boot. On the other hand, if you're talking about plant growth rates or something, then you'd need night to be what, root 2 as long as normal?, or else have semitranslucent shades for morning/evenings, which is not what Niven describes (afair).

Date: 2009-01-22 06:22 am (UTC)
From: [identity profile]
Fair enough--the outside of the ring is made of unobtainium anyway. I guess I can move on to wondering why the sky isn't white, given that the atmosphere is 1000 miles thick...

Niven is pretty explicit about the day/night transitions being abrupt. I can't remember if he ever says outright that day and night are supposed to be the same length, but given that his recurrent adjective for describing the terminators is "checkered" it's pretty heavily implied.

Date: 2009-01-22 05:47 pm (UTC)
From: [identity profile]
I believe it is explicitly mentioned that the sun squares vary in length (or at least are further away/closer to the sun, which would be equivalent), which provides seasons as the days lengthen and shorten. I do not believe that the average length is mentioned, but I think it's assumed to be 12.

Is it mentioned that the sun's the same brightness and distance as Earth's? I don't remember that being there specifically.

Date: 2009-01-22 06:03 pm (UTC)
From: [identity profile]
ISTR the intro to one of the books saying that the ring is 1AU out from the sun. I don't think there's any specific description of the sun itself, but I'd imagine that the distance requires a Sol-like sun.

Date: 2009-01-22 06:19 pm (UTC)
From: [identity profile]
Given the rotational velocity, the radius of the Ringworld is definitely about an AU, unless it's supposed to have substantially non-Earthlike gravity. I'm not sure about the sun, but I seem to recall there being a line near the beginning about it being Sol-like. Unfortunately I returned my copy to the library yesterday...


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