Thread: Cidri Genesis
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Old 05-31-2019, 01:21 AM   #59
Join Date: May 2015
Default Re: Cidri Genesis

Originally Posted by TippetsTX View Post
While I tend to read the sentence "Cidri is big enough to hold thousands of Earths" as hyperbole, for the sake of argument, let's say that Cidri is roughly the size of Jupiter (which can hold 1300 or so Earths, volume-wise). The surface area, then, would be about 120 times that of Earth with a radius of 43,000 miles.

So if I'm doing the math right (which is doubtful), a sailor in a crow's nest 100 ft above sea level on Cidri should be able to see nearly 40 miles in all directions assuming favorable atmospheric conditions. That's about twice as far as would be possible on Earth. I was expecting a larger number TBH, but does that sound about right to the rest of you?
The math is straightforward.

The distance you can see before the horizon interferes is the square root of ((your height above the surface plus the diameter of the planet) times your height again). (For more math fun, see for example .)

I think your math is in the right ballpark. I get 47 miles on Jupiter's surface (...) from 100 feet up, as opposed to 12 on Earth.

Say you find a small easily climbed mountain, say 4000 feet. On Earth, you could see 77 miles to the horizon, barring clouds. On Jupiter, that would be 301 miles.

Also, perhaps more relatable to appreciate the experience, a few two meters off the ground on Jupiter would have a horizon as far as someone 100 feet up on Earth (about 12 miles, as you wrote before).

As for whether an all-in-one Cidri would be bigger than Jupiter or not, I would say so (but again, I really think Cidri is thousands of mostly normal-sized worlds linked by gates). I don't think it means holding thousands of Earth inside it, but that the surface would provide room for thousands of Earth-sized surfaces. (Maybe quite a few thousands, if it's really going to hold everyone's Cidri campaigns.) Jupiter's surface area is only 228 times Earth's surface area.

A planet with the surface area of two thousand Earths would be almost three times the diameter of Jupiter in size. On such a planet:

The horizon at 2 meters up is 21 miles. (3 on Earth)
The horizon at 100 feet up is 81 miles. (12 on Earth)
The horizon 4000 feet up is 518 miles. (77 on Earth)
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