- Thread starter
- #21
Kaellpae
Grandmaster
I like the idea of a darker second moon that gets lost. Would it need to share a path with the primary moon?
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Calendar Causing Event
- Thread starter Kaellpae
- Start date
Nah, just makes it simpler to work out. That, plus I wanted to be able to have some clear idea exactly how large each one could/might look, by starting with the assumption that they were identical. Saves a whole mess of figuring. Don't need to stay with that assumption: as mentioned before, that was just to have a place to start from. They would probably share a "path," in the sense that they would seem to cross the same part of the sky; even that isn't an absolute necessity if they're different sizes, though it would be by far the most likely scenario. (If the moons formed naturally at the same time the planet did, they'll orbit pretty close to directly around the planet's equator, and in the same direction as the planet's rotation, regardless of size, distance, period or anything else.)
In reality, the chances of two moons of like mass forming at exactly the correct places to share the same stable orbit are… well, "astronomical"—even in astronomical terms. Probably a bit beyond even that, unless there were yet another moon, far more massive than those two, in still more distant orbit: then it can be done fairly easily. In the end, it would be considerably more realistic for the two moons to orbit at different distances; we have hundreds of good examples of those. Also, the situation of losing the more distant one would be less likely to raise questions among science geeks.
[If anyone's seriously interested in the details, I put the hypothetical starter moons at L4 and L5. That's "Lagrangian points," for non-SciFi readers.
And if you're super-seriously interested, and want to know why we know it works, you can also check "Trojan objects." Though it may be worth noting that all such cases we're aware of do have that more distant, massive body stabilizing those orbits. I can't see any reason why a similar situation couldn't develop without one, but it's quite possible that the separation between the two moons would be some angle other than 120°. In fact, I really—and deliberately—chose the "worst-case" scenario when it comes to astrophysical possibility. Figured if it could be made plausible even there, getting it to work under more normal conditions would be a breeze.]
If they were at two different distances, the more distant one would have almost certainly have had a longer orbital period, barring some seriously bizarre differences in masses. (Don't ask. Just didn't want you to think I'd overlooked the possibility.) On the other hand, there's no reason why our cultures necessarily used either of them to create a "month": if one orbited in 4.7 days and the other in 96, it's not too likely either would have been considered particularly useful. We might not have had "months" at all, and divided our year in completely arbitrary fashion. On the other other hand, if the second one were far enough away to have that slow an orbit, it's also not too likely losing it would have been much more than visually disturbing; the physical effect on the planet would have been far less. So it probably shouldn't have been too far out. I'd suggest that the whatever the choices are, the more distant one have an orbital period 1.5x the nearer one—so if the nearer one went around in 24 days, the distant one would have gone around in 36. (Yes, there's a reason. No, I'm not going to try to explain it. If you made it past Lagrangian points, you'll be able to find it on your own. )
However… if what you want to know is how big each one looked, or how fast the remaining one goes around our planet now as opposed to then, the answers are pretty much:
(1) any way you want; and
(2) not a whole lot different than before.
I'll happily point out anything egregious—don't have each of them take up a quarter of the sky, or be plaid, or have orbital periods better measured in hours or decades than in a few dozen days—but apart from that, it actually doesn't matter a whole lot unless you really want to get into the details of astrological conjunctions that can no longer happen, or something of that sort. (I'm sure our cultures needed to raise a completely new generation of astrologers, by the way. They may still not have it right… how reliable have their predictions been for you recently? )
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desertrunner: I'd have to crunch up a few more numbers than I have readily available, but I'm not sure that even the kind of tug we're talking about could raise anything the size of your island out of the depths. [No, that's being polite: I'm quite sure it couldn't—based on any process ever observed on Earth. I make your land out to be somewhere in the vicinity of 110,000 square miles or so, on a very quick-n-dirty estimate. Knocking something into the ocean isn't all that difficult, but normal tectonic processes would take megayears to accomplish raising it. Just sayin'.…] I have a couple of ideas how we might be able to get around that, or at least some part of it, but you may not want to grow irrevocably attached to the notion. Not enough time to do all the checking tonight, at any rate, so maybe I'll dream something up in the meantime… literally or otherwise. 'Night, y'all.
In reality, the chances of two moons of like mass forming at exactly the correct places to share the same stable orbit are… well, "astronomical"—even in astronomical terms. Probably a bit beyond even that, unless there were yet another moon, far more massive than those two, in still more distant orbit: then it can be done fairly easily. In the end, it would be considerably more realistic for the two moons to orbit at different distances; we have hundreds of good examples of those. Also, the situation of losing the more distant one would be less likely to raise questions among science geeks.
[If anyone's seriously interested in the details, I put the hypothetical starter moons at L4 and L5. That's "Lagrangian points," for non-SciFi readers.
And if you're super-seriously interested, and want to know why we know it works, you can also check "Trojan objects." Though it may be worth noting that all such cases we're aware of do have that more distant, massive body stabilizing those orbits. I can't see any reason why a similar situation couldn't develop without one, but it's quite possible that the separation between the two moons would be some angle other than 120°. In fact, I really—and deliberately—chose the "worst-case" scenario when it comes to astrophysical possibility. Figured if it could be made plausible even there, getting it to work under more normal conditions would be a breeze.]If they were at two different distances, the more distant one would have almost certainly have had a longer orbital period, barring some seriously bizarre differences in masses. (Don't ask. Just didn't want you to think I'd overlooked the possibility.) On the other hand, there's no reason why our cultures necessarily used either of them to create a "month": if one orbited in 4.7 days and the other in 96, it's not too likely either would have been considered particularly useful. We might not have had "months" at all, and divided our year in completely arbitrary fashion. On the other other hand, if the second one were far enough away to have that slow an orbit, it's also not too likely losing it would have been much more than visually disturbing; the physical effect on the planet would have been far less. So it probably shouldn't have been too far out. I'd suggest that the whatever the choices are, the more distant one have an orbital period 1.5x the nearer one—so if the nearer one went around in 24 days, the distant one would have gone around in 36. (Yes, there's a reason. No, I'm not going to try to explain it. If you made it past Lagrangian points, you'll be able to find it on your own.
)However… if what you want to know is how big each one looked, or how fast the remaining one goes around our planet now as opposed to then, the answers are pretty much:
(1) any way you want; and
(2) not a whole lot different than before.
I'll happily point out anything egregious—don't have each of them take up a quarter of the sky, or be plaid, or have orbital periods better measured in hours or decades than in a few dozen days—but apart from that, it actually doesn't matter a whole lot unless you really want to get into the details of astrological conjunctions that can no longer happen, or something of that sort. (I'm sure our cultures needed to raise a completely new generation of astrologers, by the way. They may still not have it right… how reliable have their predictions been for you recently?
)•
desertrunner: I'd have to crunch up a few more numbers than I have readily available, but I'm not sure that even the kind of tug we're talking about could raise anything the size of your island out of the depths. [No, that's being polite: I'm quite sure it couldn't—based on any process ever observed on Earth. I make your land out to be somewhere in the vicinity of 110,000 square miles or so, on a very quick-n-dirty estimate. Knocking something into the ocean isn't all that difficult, but normal tectonic processes would take megayears to accomplish raising it. Just sayin'.…] I have a couple of ideas how we might be able to get around that, or at least some part of it, but you may not want to grow irrevocably attached to the notion. Not enough time to do all the checking tonight, at any rate, so maybe I'll dream something up in the meantime… literally or otherwise. 'Night, y'all.
desertrunner
Journeyman
If it doesn't work it doesn't work. I've still got 3 geothermal springs providing water for my island.
- Thread starter
- #24
Kaellpae
Grandmaster
If your guild is the first to occupy it, then why not have them spread a rumor that it surfaced not long ago? It could be that nobody ever came close enough to the island to notice it.
My island is only recently repopulated because of the massive volcanic explosion when our moon disappeared. The explosions destroyed a settlement, and it took, oh.. 100 years for them to come back and start to establish the only city on the island, currently. A second may be developing in the north.
My island is only recently repopulated because of the massive volcanic explosion when our moon disappeared. The explosions destroyed a settlement, and it took, oh.. 100 years for them to come back and start to establish the only city on the island, currently. A second may be developing in the north.
Donny Bruso
Mystagogue
But Rav, I so wanted a plaid moon... You're taking all the fun out of this, lol.
You're taking all the fun out of this, lol.
Perhaps I should have said that it depends on the kind of plaid you want. Find some images of Europa. Not exactly a tartan, but with a little imagination.…
•
The biggest problem with people "not noticing" desertrunner's island is that it's right in the middle of things. Kinda hard to miss. Especially since it's about halfway between New Zealand and Italy in total area, based on how it appears on the map at the moment.
I can think of a few reasons it might not have been particularly popular (or populated) in the old days. First, it might have been considered largely worthless—a bit of a stretch, considering how quickly any land, no matter how lousy, tended to get snatched up in feudal societies. There are ways to make it plausible, though. One is that there were reasons to avoid it: hostile natives, monsters, etc. Another is for it to lack any redeeming value that would overcome those reasons: minimal water sources, poor cropland, much of the native flora was poisonous.
The second possibility is an outgrowth of the first: it was considered largely worthless—until your people discovered whatever it is that makes it worth the effort of having now. Also, if the archipelago lost significant amounts of land during the cataclysm, that would make any remaining land more valuable, no matter how marginal it might have been… as well as leaving a large number of survivors with devastated homes.
Third, some of the factors that made it difficult before could have changed. Most or all of the hostile natives/frumious bandersnatches/whatever could have been wiped out during the cataclysm, for instance. The springs providing your water might not have been active, or may have been much smaller, in the past: all that shaking around rearranged things enough that larger quantities of water (and possibly better water) got forced to the surface, making large-scale settlement more practical.
Fourth—and this is what I was originally going to suggest last night, except that it was getting late—it's possible that some of the land is "new," but not all of it. (This would address some other problems, too: they'll be mentioned as they come up.) For instance, say that the central and southwestern parts of the island were there before (and may have suffered from any of the foregoing circumstances), but that the areas to the northwest and/or the eastern peninsula were shallows, either large underwater flats or perhaps tidal swamps, with the occasional rocky outcropping jutting up above water to make the areas hazardous to navigation… and at the same time preventing the shallows from being eroded by sea currents. When the cataclysm hit, these areas were lifted just enough that they are now a few feet above water rather than a few feet below it.
[Even that would have caused some very impressive tsunamis to radiate outward from the uplifted areas. Lifting the areas I proposed—roughly 70,000 square miles—would displace over a third of a billion cubic feet of water per foot they were raised. Not on the level of the 2004 Sumatra quake… but that was also spread out over a vastly larger area: our entire map is less than a quarter the size of the Indian Ocean, and the areas that would have been affected are only about 20% of the map. (For comparison purposes: if that land were raised a bit less than half a mile, it would exceed the Sumatra quake… in an area 5% of the size of what that affected.)]
These areas would necessarily still be largely marginal, if you went this route: three centuries isn't enough time to change a sandbar into fertile farmland. Some vegetation would spread quickly—sea oats, lichens, and the like; extensive hardwood forests… not so much. (One of the problems that can be addressed by having part of the island exist before: those areas would be like any other land.) The "new" land would be mostly flat, and not much above sea level; some parts may still be (or have become) tidal swamps. This could explain why such a large area didn't receive much attention before: all you have to do then is explain why the older, higher ground was less than popular. Even so, pretty much anything of "value" would have to be located in the older areas. Sometimes you can find nifty things buried in the sand… but it's not a good way to bet. (Really, you'd be better off having a bunch of the old land surface washed away by tsunamis, exposing things no one realized were there before. But I don't know what it is you were planning on in terms of "riches," so I couldn't make any recommendations there. If you want some ideas of things that might work—or want to check what you already had planned—might be better to PM me, just so we don't stray too far off topic.… )
And, of course, all the above comes with the caveat that this is a fantasy setting, so it doesn't have to work the same way Earth does. I just figure the more that can be solidly grounded in "reality" (or at least hanging on to reality by one toe while straddling the gap to imagination), the better.
•
The biggest problem with people "not noticing" desertrunner's island is that it's right in the middle of things. Kinda hard to miss. Especially since it's about halfway between New Zealand and Italy in total area, based on how it appears on the map at the moment.
I can think of a few reasons it might not have been particularly popular (or populated) in the old days. First, it might have been considered largely worthless—a bit of a stretch, considering how quickly any land, no matter how lousy, tended to get snatched up in feudal societies. There are ways to make it plausible, though. One is that there were reasons to avoid it: hostile natives, monsters, etc. Another is for it to lack any redeeming value that would overcome those reasons: minimal water sources, poor cropland, much of the native flora was poisonous.
The second possibility is an outgrowth of the first: it was considered largely worthless—until your people discovered whatever it is that makes it worth the effort of having now. Also, if the archipelago lost significant amounts of land during the cataclysm, that would make any remaining land more valuable, no matter how marginal it might have been… as well as leaving a large number of survivors with devastated homes.
Third, some of the factors that made it difficult before could have changed. Most or all of the hostile natives/frumious bandersnatches/whatever could have been wiped out during the cataclysm, for instance. The springs providing your water might not have been active, or may have been much smaller, in the past: all that shaking around rearranged things enough that larger quantities of water (and possibly better water) got forced to the surface, making large-scale settlement more practical.
Fourth—and this is what I was originally going to suggest last night, except that it was getting late—it's possible that some of the land is "new," but not all of it. (This would address some other problems, too: they'll be mentioned as they come up.) For instance, say that the central and southwestern parts of the island were there before (and may have suffered from any of the foregoing circumstances), but that the areas to the northwest and/or the eastern peninsula were shallows, either large underwater flats or perhaps tidal swamps, with the occasional rocky outcropping jutting up above water to make the areas hazardous to navigation… and at the same time preventing the shallows from being eroded by sea currents. When the cataclysm hit, these areas were lifted just enough that they are now a few feet above water rather than a few feet below it.
[Even that would have caused some very impressive tsunamis to radiate outward from the uplifted areas. Lifting the areas I proposed—roughly 70,000 square miles—would displace over a third of a billion cubic feet of water per foot they were raised. Not on the level of the 2004 Sumatra quake… but that was also spread out over a vastly larger area: our entire map is less than a quarter the size of the Indian Ocean, and the areas that would have been affected are only about 20% of the map. (For comparison purposes: if that land were raised a bit less than half a mile, it would exceed the Sumatra quake… in an area 5% of the size of what that affected.)]
These areas would necessarily still be largely marginal, if you went this route: three centuries isn't enough time to change a sandbar into fertile farmland. Some vegetation would spread quickly—sea oats, lichens, and the like; extensive hardwood forests… not so much. (One of the problems that can be addressed by having part of the island exist before: those areas would be like any other land.) The "new" land would be mostly flat, and not much above sea level; some parts may still be (or have become) tidal swamps. This could explain why such a large area didn't receive much attention before: all you have to do then is explain why the older, higher ground was less than popular. Even so, pretty much anything of "value" would have to be located in the older areas. Sometimes you can find nifty things buried in the sand… but it's not a good way to bet. (Really, you'd be better off having a bunch of the old land surface washed away by tsunamis, exposing things no one realized were there before. But I don't know what it is you were planning on in terms of "riches," so I couldn't make any recommendations there. If you want some ideas of things that might work—or want to check what you already had planned—might be better to PM me, just so we don't stray too far off topic.…
)And, of course, all the above comes with the caveat that this is a fantasy setting, so it doesn't have to work the same way Earth does. I just figure the more that can be solidly grounded in "reality" (or at least hanging on to reality by one toe while straddling the gap to imagination), the better.
- Thread starter
- #27
Kaellpae
Grandmaster
I probably should have looked to see which island was in question. Pretty sure when I posted that it was past my naptime.
myrddin173
Scribal Lord
Thank you Ravana for explaining all of that. Now we can't let that go to waste so of course the disappearing moon now exists or rather existed around 311 years ago. Anyways I always figured that my "rational" islanders didn't like each island having its own calender and were just waiting for an excuse to make a universal one. They would be like, "Oh something bad happened... We should make an inter-island calender! Woohoo!"
P.S. I would totally vote for a plaid moon!
P.S. I would totally vote for a plaid moon!
Okay: you want me to knock out an "official" (subject to approval) version of what happened… phrasing it in terms our natives would understand?
(I can get to work on a plaid moon, too. You want it to have always been that way, or only recently? I can do either.)
(I can get to work on a plaid moon, too. You want it to have always been that way, or only recently? I can do either.)
- Thread starter
- #30
Kaellpae
Grandmaster
That would greatly improve my ability to get a personal history going.
Color of the moon doesn't matter to me. I was partial to a white and a red one. Really though, as long as it's there.
Color of the moon doesn't matter to me. I was partial to a white and a red one. Really though, as long as it's there.