Columbus discovers the Loon?

So, there's this sun-like star out there somewhere, which we shall call Los. The Losar system is identical to the solar system in every particular except for one thing - the third planet, Learth, instead of having a tidally locked satellite, is itself the tidally locked satellite of a gas giant, which we shall call Loon.

Due to the tidal lock, and ignoring complications such as libration◊ for the moment, Learth has a Loonlit hemisphere (the one which would be visible to an observer on Loon, corresponding to the Moon's "near side") and a Loonless hemisphere (invisible from Loon, like the Moon's "far side").

The Loonlit hemisphere is mostly water, though it has one major landmass stretching most of the way from the northern to southern pole. The water to the west of this landmass is called the Lacific ocean, the landmass itself the Lamerican continent, and the water to the east the Latlantic ocean. The Loonless hemisphere is mostly land, in the form of one supercontinent - Lafro-Leurlasia.

a) The intention, as should be obvious by now, is to make Learth as much of an Earth-clone as possible. Other than the obvious difference to the visible night-sky and having Losar instead of Loonar tides, which other differences are absolutely unavoidable? I'm pretty sure the day has to be a lot longer than 24 hours for the orbit to fall outside the Roche limit, for one, which would affect the weather. On the other hand, I don't see any obvious reasons for the seasons not to work just as they do on Earth; one just needs to incline Learth's orbital plane about Loon by the same amount as its rotation axis, with respect to the Loon's orbital plane about Los (which one might call the "Lecliptic", but that's probably more confusing than useful). What else?

b) Making the assumption that in spite of those differences, life and eventually Lumans evolve on Learth, is it plausible that the inhabitants of the Loonless hemisphere would never figure out or even suspect that Loon exists until their Columbus sails to Lamerica and "discovers" it? I'm thinking yes - after all, the leading astronomical model on Earth, in Columbus' day, posited "spheres within spheres" even though there weren't any. Ironically, Learth's orbit really could be modelled as "a sphere within a sphere", thus potentially revealing the presence of an invisible attractor on the other side of the planet. But no doubt Lumans would insist on a Learth-centric universe and screw it up anyway. [tongue]

c) Assuming that the above holds and their Columbus returns with tales of this giant disk looming (or Looning, rather) in the skies over Lamerica, what sort of societal impact, if any, might that discovery have, once it is widely believed?

I love how you have the letter 'L' at the beginning of all your words :P

I would imagine the discovery that their world orbits another would come as a shock and forever alter how the Lumians percieve their world but at the same time would probably have the Lumian scientists going 'Aha, that explains why...'

In RL here are always lotsa rumours and prophecies floating round about when and how the world will end so you could have a group of Lumians that start to worry about the possibility that their worlds will orbit slowly detieriorate and crash into the gas giant which they orbit. Then tye Lumian scientists would be saying theres no evidence to support that and the group woudl be 'how do you know if its only just been discovered you havent had any time to properly observe its affects upon our world and it says in this old prophecy carved into a temple by a much earlier more primitive socioty that our world will end by crashing into that which it orbits!'

Also are the Lumians all one nation/culture or many that coexist? Cause Columbus wasnt the first to discover America there were settlers from other countries like Vikings etcetera so its possible a nation/culture nearer to Lamerica is kinda aware of the whole orbitting a gas giant because of previous explorers bring tales home but that was long enough age and the country hasnt done any exploring since that the other nations/cultures dismiss it as exaggerated fairy tales. Then when it is discovered that country can be all 'told ya so'

Technological progress is not as linear as Civilisation games suggest. ;) The best astronomical models in Columbus' time would probably have been those of the south american cultures, and they were pretty advanced. Anyway, point being: it is certainly possible that some culture develops sufficient naval architecture to create ships that can sail around the plant (and then does so) without having developed the mathematical and astronomical knowledge that'd make them suspicious about the planetary orbit. Heck, the Romans had no decent number system, but they did have concrete and built huge structures. You're not going to have a cultue with computers without also having a solid grasp of the scientific method, but most human discoveries made up to and during the renaissance can be made simply by trial and error.

On another note, i'd be curious how a gas giant would actually show up in the sky. I'm too lazy to do the orbital distance/period calculations myself, but i suspect that would have dramatic influence on the climate.

edited 23rd Aug '12 6:01:19 AM by McKitten

*shrug* It's a useful naming technique, especially if one doesn't mind being whimsical. Takes hardly any creativity to apply, since all one is doing is taking an existing nomenclature and modifying it, and the results transparently relate to both their real-world counterpart and the commonality which sets them apart, so the readers don't have to memorize anything but can figure out every instance effortlessly.

For the sake of simplicity, let's continue my approach and say they're just as diverse as humans are (were).

"Columbus", in this context, simply means the first person who travels to Lamerica, returns, and whose discoveries are then both widely disseminated and widely believed. So, the ancestors of the Native Lamericans don't qualify on the second count, and the Likings don't qualify on the third count IF history plays out as it did on Earth. Would the Vikings' transatlantic journeys have had a very different impact if they'd discovered something as spectacular as the Loon, rather than just another shore (for all they knew)? I have no idea - that's why I started this thread!

Mind you, there is at least one little flaw in my scenario: If Leurlasia is just like Eurasia, then the continent itself actually extends across a bit more than one hemisphere.

I'm not sure how significant this is; if one can places the division just right (at about 25 degrees West - 155 degrees East◊), the only bits that stick into the Loonlit hemisphere would be Leenland in the West, in as far as that counts as part of Leurlasia, and Lamchatka and whatever the North-Eastern-most tip of Lasia is called (I thought that was part of Liberia (heh), but apparently it's not) in the East. Both of those places were still more or less terra incognita at the time in question, so this may not matter. Then again, it may, if the very fact that one can see the Loon from there impacts historical events during earlier times.

edited 23rd Aug '12 7:40:09 AM by kassyopeia

Alright, alright, I'll overcome by laziness and give you some quantitative data, then. Let's say the gas giant is a Saturn-clone, since that one has lots of conventiently round numbers describing it: Mass just about 100 times Earth's, radius just about 10 times Earth's, surface gravity just about the same as Earth's.

Naively, that means that Learth could orbit the Loon so closely that their atmospheres almost touch, and would still maintain gravitational integrity. That, of course, would mean that the Loon covers almost the entire sky, if you stand right underneath it. Which means that day and night would in effect be reversed, as sunlight would mainly get to you by first reflecting off the Loon, rather than directly.

Practically, I'm sure that wouldn't work. What does work, to my surprise, is an orbital distance which results in a 24-hour day - Mimas is even slightly below that. Let's definitely use that, then, in the spirit of making Learth as Earth-like as possible. This would correspond to an orbital distance of

G M / a^2 = v^2 / a = ((2 pi a)/(1 day))^2 / a
a^3 ~ (1/(4 pi^2)) G M (1 day)^2 ~ 7*10^24 m^3
a ~ 2*10^8 m ~ 30 R_learth ~ 3 R_loon ~ 1/2 d_Earth-Moon

That should mean that Loon as seen from Learth subtends about (2/3)^2 / (2 pi) ~ 10% of the sky, or analogously appears on the order of 1,000 times bigger than our Moon. Consequently, inloonation (incident energy of Loonlight) should be several percent of inlosation (incident energy of Loslight), which should make Lamerican nights as bright as very overcast days. Temperature-wise, that still doesn't make much of a difference, though, I think.

Tidal forces scale as M/d^3, so the Loonar tidal bulge would have a height of (10^4/(1/2)^3) * (30 cm) ~ 30 km or thereabouts. Since Learth is tidally locked, that bulge isn't going anywhere and so doesn't cause tides in the conventional sense. However, eccentricities in the orbit would cause fractional changes in the height of the bulge and cause tides that way. The orbital radii of the Earth about the Sun and of Mimas about Saturn both vary by about 1%, so we might as well use the same value for Learth about the Loon, which would mean tidal amplitudes of as much as several hundred metres in the central regions of both hemispheres, i.e. at the Lamerican west coast and along all Lindian ocean coasts, and at least several dozen metres along all other coasts. Yikes.

The reflected light itself wouldn't cause changes in the climate, but the shadow of the gas giant could (if it's orbiting too close). Worst case would be that the side facing the gas giant will never get direct sunlight, because it's either facing away from the sun, or inside the the shadow of the gas giant. Slightly less worse cases involve a total eclipse every mid-day, length of that depending on distance to the gas giant.

Good point. Let's see... the total circumference of Learth's orbit is ~20 R_loon or so. Assuming no significant inclination to the ecliptic, ~2 R_loon of that are in the gas giant's shadow.

That should directly mean that Learth's total daily insolation is 10% lower than Earth's. Temperature depends on incident energy to the one-fourth power, so this means a ~2.5% lower global mean temperature, which translates to 7.5 degrees Celsius instead of 15 degrees Celsius. Rather a lot, actually.

Longitudinal heat exchange is quite a bit more efficient than latitudinal (Coriolis belts versus Hadley cells), so this wouldn't be an effect localized to the Loonlit hemisphere but be spread across the whole planet, to some extent. I have no idea how to estimate this properly, but for the sake of simplicity, let's split the difference and call that 5 degrees Celsius for the Lamericas and 10 degrees Celsius for Lafro-Leurlasia.

Roughly, temperatures decrease by 1 degree Celsius for every 2 degrees of latitude one moves away from the equator (from an annual mean of ~30 degrees to one of ~0 degrees as one moves from the equator to the arctic circles). 2 degrees of latitude are about 200 km. So, in the Lamericas, places would typically be as cold as places 20 degrees of latitude or 2,000 km farther pole-wards in the Americas; in Lafro-Leurlasia, it'd be 10 degrees of latitude or 1,000 km.

Which, incidentally, settles one of the points that came up earlier - the Likings probably wouldn't have been the ones to discover the Loon, since the Northern Latlantic ought to be too icebound year-round to allow much in the way of naval activities, if this difference is taken into consideration. Columbus himself should be fine, he'd just depart from a Spain that is temperate rather than subtropical and arrive in a Gulf of Mexico that's subtropical rather than tropical, but probably no worse for that.

To ameliorate the eclipses significantly for at least part of the year, Learth's orbit about the Loon would have to be inclined by at least 15 degrees with respect to the Loon's orbit about Los. At 30 degrees inclination, part of the year would have no eclipses at all. All of those values are equally plausible, as far as I'm aware. Seems to me the overall simplest choice would be that which produces Earth-like seasons. Hmmm. The maximum eclipse length coincides with the equinoxes, i.e. spring and autumn, the minimum eclipse length with the midsummer and midwinter days, if I'm visualizing this correctly. So, we can't really have "Earth-like" in this case. What we can have are annual means a little closer to Earth's at the price of rather asymmetric seasons: Cold spring, hot summer, cold autumn, mild winter. I guess that'll have to do.

On a different note, why not just have Learth have a moon in a geostationary orbit. (or would that be leostationary) If the main purpose is to have only one hemisphere with a visible moon in the sky, that seems simpler. Although it would be reeeally close for a natural satellite. Still, not that much less problematic than having life on a gas giant moon. (living on a planet that not only doesn't have a moon to catch asteroids but actually catches them for another planet would make life ... interesting)

edited 23rd Aug '12 2:17:46 PM by McKitten

Well, the whole point of the exercise is to create an event, "the discovery of the Loon", which has a real psychological impact.

"There is a moon" is something that has real significance only to astronomers; mostly everyone else would just have shrugged their shoulders and gotten on with their own affairs, I think. However, "This is a moon" might be startling enough to elicit some sort of reaction from anyone, I think.

Admittedly, the conceptual difference between the two cases isn't quite as big as that's making it sound, especially to people which are still thinking in learth-centric terms. So it'd be more about how visually impressive the thing in the sky is. A rocky moon is impressive, but pales in comparison with Los itself. A gas giant, though, is arguably even more impressive than a sun, considering the sheer angular size and level of surface detail one ought to be able to see.

Well, a loon on leostationary orbit would be quit a bit bigger than the one we have. Angular size something like 10x the size of ours i think.

I'd wonder a bit about the "we're on a moon" part. Were any moons besides the obvious one known in 1490? I suspect not, so the reaction of people would in that case probably be less "we're on a moon!" and more "holy shit, the sky is falling!" Especially if it's a really big moon. Granted, learth should have plenty of other moons visible (Saturn is too big to have only one even if it's earth-sized) but they'd just be moving points of light in the sky, without knowing of the gas giant itself, how would they come up with the idea of moons. The geocentric model after all isn't just about earth being in the centre, it is also about the "common-sense" idea that everything in the universe circles around a point in the centre. For (other) moons to make sense, one has to discover that stellar object can orbit one another, not just the centre of the universe, which is separate from the discovery that earth isn't at the centre.

Good point. And there's nothing stopping us from increasing this loon's size by a factor of 2 or 3, as far as I know (cf Pluto-Charon). Cumulatively, that would give us a disk just as big at the gas giant I had in mind. Thanks for pointing that out, it never occurred to me.

Galileo discovered the first of the Jovian moons, and he lived after Columbus. So, no.

No, in this hypothetical, the gas giant has no other satellites or rings or anything like that.

Very good point. The concept wouldn't exist for them at all, absent any visible examples.

And considering further that the Loon doesn't show motion, they probably wouldn't think of it in planetary terms at all. They might think it's a hole in the sky, and that the surface detail is part of the "eternal fire" (or whatever) that's behind the celestial sphere across which Los and the other planets and stars move. Or, assuming that they do think of the Learth as spherical, they might think it's some sort of support which the planet rests on. Like the palm of a hand supporting a basketball, if you see what I mean. This latter interpretation might be quite appealing, since it would make their hemisphere the "upper" one, as it should be.

Again, thanks, I've definitely been thinking in insufficiently historically-conscious terms so far.

I'm reminded of Dante I think describing purgatory as Jerusalem's antipode.

If the discovery was made pre-scientific revolution, and if they had the common earth belief that Heaven=Up and Hell=Down, and they knew their world was round, they might think it's the entrance to Hell, just as their own sky is the entrance to Heaven.

Needless to say, they wouldn't be overly friendly with the people living on the other side, but they might be too afraid to attack them or colonize their lands right away.

edited 6th Sep '12 2:57:01 PM by Topazan

Heh. This is a completely new idea to me, not yet having read the Divine Comedy. I always just figured Heaven equals skywards and Hell equals groundwards - which means up and down for a flat Earth but outwards and inwards for a round Earth. The other wiki re "Purgatory as a physical place":

Which, in turn, now brings Stargate's Netu to my mind.

Anyway, "entrance to hell" would seem to be the logical extension of what I suggested in the previous post, wouldn't it. It's qualitatively like Heaven, but it's on the wrong side of the planet and it's the wrong colour, so Hell seems like the most natural of associations, now that you've mentioned it.

If one adopts that interpretation, the question becomes once again what sort of consequences it would have. I'm thinking it wouldn't be enough to keep away the Conquistadors, but on the other hand it's difficult to imagine the Puritans voluntarily emigrating to what would surely become known as the "Infernal Hemisphere"...

Yeah, I'm probably over-estimating the fear they'd have of the Loon. I'm personally terrified of gas giants, so I could be projecting.

My prediction:

The Church opposes all further exploration or colonization. Slave-taking is allowed in order to save the souls of the infernal peoples, but they don't do well in Leuropean society given their susceptibility to disease.

However, unlike Lapan or Lhina, Leurope is too divided to successfully institute a ban on travel. People will still travel to Lamerica to bring back gold or forbidden culinary delights. The difference is that the motivation will be purely personal profit, and it will be done by people who have for whatever reason rejected the values of their home society. This could mean that Lamerica would be culturally distinct from Leurope, in contrast to the Anglicized North America and Catholic South.

In addition, I'd expect some major religious discord in Leurope if the colonists are successful. Whether it would strengthen or weaken the Church I don't know.

It might leave the Lhurch in a lurch. Hardeeharhar.