Explain to me again, how we know the Earth to be banana shaped.

[knasser]

So, I have noticed that my players are predisposed to make real world assumptions about the setting. E.g. one keeps asking me about whether the speed of a falling druid changes when they turn into a bear. To which, although it was painfully transparant that they thought they were executing some clever trap, I said "no, the speed of the falling druid does not change". At which point a small victory dance was performed because they had found a way to cheat conservation of momentum. (So what? Magic supplies extra energy - it's magic). I think they have some weird idea that they will utilize this somehow.

Anyway, along this theme, I feel like tweaking their noses a little until the episodic pain conditions them to stop taking things for granted. Example: the Sun goes around the world, not the other way around. The game is currently fairly low fantasy so they wont be flying high into the sky in an airship. Are there any consequences to the Sun being a small (in relative terms) globe of fire orbiting the world that would be visible from the ground? I presume that the our own real-world ancients worked out that it wasn't through some observational means that distinguishes the earth going around the Sun from the other wary around. What was that? N.b. I still want to have seasons in this setting, so I guess my sun's orbit must be eccentric.

I'm also toying with the world being flat. I also need to work out what stars are because they are most definitely not distant suns of their own. Or at least not in the giant sense - they could well be nearer and smaller balls of fire.

Any thoughts on observable effects to the common sage who lacks a space program and GPS that are consequences of these things? Also, any other ideas of discredited ideas that could be made to work in a medieval fantasy setting would be welcome if you have them!

Peace and coolness,

K.

 

[fuindordm]

Any departure from real-world physics is going to require magic to do some heavy lifting to keep the world in place. This is not a problem, and I think you have the right idea.

The ancient Greeks did debate the question of whether the Earth went around the Sun or vice versa. The proof they looked for was parallax in the stars: if the Earth goes around the Sun, they reasoned, then they should be able to observe the apparent position of the stars changing slightly due to the different viewing angle. Since they could observe no parallax, they (that is, the majority of philosophers arguing about such things at the time) concluded that the Earth was fixed. More precisely, they calculated a minimum distance for the stars that would make the parallax unobservable. This number was so much larger than the diameter of the Earth that they thought it nonsensical. Of course, modern telescopes are able to observe parallax to the closest stars, and now we have come to terms with the scale of the universe, but I feel sympathy for the Greeks who balked at the idea.

The answer to your question depends also on how complicated you want the sky to be. A sunlike moon orbiting the Earth could indeed keep it warm. You could explain seasonal variations with an elliptical orbit as you suggest, or as a regular fluctuation in the sun's output, like a beating heart. Are there other planets in the sky? A regular moon? A bright Jupiter roaming the sky, or a Venus-like evening/morning star? A blood-red Mars? The scientists of your world can easily verify that they are the center by observing the phases of the other celestial orbs as they change their position with respect to the Sun; indeed, the first nail in the coffin of the heliocentric model in our world was Galileo's observation of the phases of Venus.

So there you have it--the key observations available to middle-age astronomers are parallax (if the Earth is moving) and phases (whether or not it is moving). What they are probably most interested in, however, is predicting the movements of any other planets across the backdrop of fixed stars. But maybe your world doesn't have stars--maybe the sky is completely black except for the moon, or maybe the backdrop is a gorgeous nebula or galaxy, or an iridescent glow like the inside of a clamshell.

Enjoy making your setting!

Cheers,
Ben

 

[steenan]

Observing that Earth is round is simpler. Choose two points, preferably on the same meridian (for ease of calculations). Measure how high above the horizon the Sun is at noon in each od them. From the difference between the angles and the distance between measurement points you can calculate the Earth's radius with not much trouble (it's distance/angle, with angle in radians). This kind of measurement has been performed successfully in ancient times, by Eratosthenes, IIRC.

 

[knasser]

Very helpful. Thank you. Also, my respect for the Ancient Greeks has grown two sizes today. And I don't blame them either for throwing out the calculated minimum distance for the stars as absurdly huge.

So the things I should note for my setting so far are
1) No parallax for the stars as they are close and fixed.
2) The sun must move on an eccentric orbit.

I'm thinking for the stars that they'll be points of light on the inside of a dark sphere. Though I also like the idea of them being celestial beings hanging out in the void. Perhaps cities. If they're fixed, e.g. on a sphere or simply maintaining the same relative positions in space, what does that do to how they look to observers. I guess my world isn't revolving if the sun goes around it. Which would mean stars don't rise or set. Or if they do, then it must mean that the celestial sphere (or the stars at least) are also orbiting around the Earth.

It now occurs to me that the Sun typically looks smaller than the moon and I have the amusing visual in my mind of an "eclipse" where the sun moves in front of the moon. Probably not something I would do, but makes me smile and it's almost tempting just to see the looks on my players' faces.

Any significant problems with a flat earth if I decide to do that?

 

[knasser]

Observing that Earth is round is simpler. Choose two points, preferably on the same meridian (for ease of calculations). Measure how high above the horizon the Sun is at noon in each od them. From the difference between the angles and the distance between measurement points you can calculate the Earth's radius with not much trouble (it's distance/angle, with angle in radians). This kind of measurement has been performed successfully in ancient times, by Eratosthenes, IIRC.

Thank you also. I guess I can't really do a flat earth because for the sun to rise and set in anything like our own world, the flat world would have to be very small, I guess. I mean, assuming the sun goes round the world.

 

[Caliban]

Thank you also. I guess I can't really do a flat earth because for the sun to rise and set in anything like our own world, the flat world would have to be very small, I guess. I mean, assuming the sun goes round the world.

You could go a little stranger - the world is ring shaped, with the sun and moon traveling around the outside of the ring at slightly different speeds. Now the world is both round (going east/west) and flat (going north/south) - with an edge you can fall off.

 

[Rune]

You could go a little stranger - the world is ring shaped, with the sun and moon traveling around the outside of the ring at slightly different speeds. Now the world is both round (going east/west) and flat (going north/south) - with an edge you can fall off.

This has long been my preferred model, from a cartography perspective). In part because of its simplicity (no distortion on maps). In part because it's easy to repurpose cardboard tubes into globes.

 

[knasser]

You could go a little stranger - the world is ring shaped, with the sun and moon traveling around the outside of the ring at slightly different speeds. Now the world is both round (going east/west) and flat (going north/south) - with an edge you can fall off.

You are Larry Niven, and I claim my 5gp.

 

[darjr]

The world is indeed flat, but infinite. Actually the universe is an infinite ocean and each world is a continent within it. Each with their own sun that surges forth a new from the ocean and is quenched each dusk. A vast god like being just illuminating their one world. Each world has their own sun that is different. One is a grand Phoenix that is born each morning and dies each night living a glorious light filled life arcing across the sky. Another is a theif who has stolen a tremendous sun fish from the depths and his eternal struggle to tame the monster plays out as the days and nights and season's. The other stars are suns that have not yet found an island world to illuminate.

There are also dark worlds with no sun. Vast dead dark continents where the dead rule.

 

[Maxperson]

Anyway, along this theme, I feel like tweaking their noses a little until the episodic pain conditions them to stop taking things for granted. Example: the Sun goes around the world, not the other way around. The game is currently fairly low fantasy so they wont be flying high into the sky in an airship. Are there any consequences to the Sun being a small (in relative terms) globe of fire orbiting the world that would be visible from the ground? I presume that the our own real-world ancients worked out that it wasn't through some observational means that distinguishes the earth going around the Sun from the other wary around. What was that? N.b. I still want to have seasons in this setting, so I guess my sun's orbit must be eccentric.

2e Spelljammer established Oerth(Greyhawk) as having a small sun orbiting it. Didn't seem to give any real consequences.