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Found 8 results

  1. Need any help with it? Come over here! Want to talk about it? This thread's for you! Want to hate on it? Go somewhere else because that's not what this thread is for. These people make excellent resources for help. Math/Calc: Chaos Classical Physics: Glamdring804 Micro/Nuclear Physics: Idealistic Mistborn Chemistry: Pagerunner Biology: Pestis the Spider Circuits: Silverblade5
  2. EDIT: Updated with some suggested numbers from the thread It is a little hard to grasp the scale of the tower city. Even Shallan can't capture it on the page! (To talk about that issue and whether it is driven by scale, psychology, or magic, see this thread.) Here are all of the physical descriptions we have of Urithiru. (If I've missed something you consider important, include a quote and I'll add it to this post. My chapter 87 quote is incomplete at the moment.) Summary: There are 10 tiers of 18 levels each, seemingly carved into the mountain. Each level is larger than the one above it, at least by the width of a balcony. The whole thing looks like The roof of the top level is ~100 yards across. The lowest level has a large plateau in front with the 10 oathgate platforms The oathgate platforms are raised 10 feet over surroundings, and are large enough to hold three armies worth of Everstorm survivors The lowest level also has large gardens/farms surrounding it. Assumptions: We have to make a lot of these. I'll update them as we get more information, or as others make convincing arguments, but for now let's go with: A Rosharan yard is close to 1 meter. Each balcony is 1.5 meters wide. Each new tier extends 20m 50m past the bottom of the one above, to accommodate gardens. Each floor is 4.5m 5.5m high, including the thickness of stone that supports the floor above. 20,000 people crowded onto the oathgate plateau at the end of WoR. (Does someone have a better number for this?) They pack closely but don't stab each other, about ~4 people/sq meter. This gives us an 80 meter diameter platform. The plateau is described as several hundred yards across, so we'll assume 300m for now. Conclusions: Using these numbers, we get a tower that is 1.5km wide at the base, and 1km high. Here's how that looks when compared to tall buildings on Earth (modified from this image on Wikipedia). A circular arrangement of ten 300m Oathgate platforms has an inner diameter of ^700m, and an outer diameter >1300m. To my mind, these are probably underestimates. As has been mentioned, Burj Khalifa is the tallest building on earth at 830 meters, and it has 160 floors to Urithiru's 180. At 4.5m per level+ceiling, I don't believe that our assumed thickness of stone has the structural integrity to hold up that massive a structure when it is filled with tunnels and cavernous spaces. Yes, surges could augment that strength, but I'm skeptical of a fabrial that would function to keep the city standing for millenia. I think we need to add more thickness to these load-bearing floors, and probably more width to the tiers. But before I modify the above assumptions, I'd like to see what the rest of you think. EDIT: Here is a perspective view of the tower and the oathgate complex. There is some disagreement in the thread about the arrangement of oathgates relative to the city, so I've included three versions here. Please comment to make your case for the arrangement you think is correct (one of these, or something different). Previous images:
  3. Edit 3: Here's a quick look into my most recent progress - labels over targets, a more detailed HUD, and several physics tweaks. I'll edit what I can from the original post, but there's a lot of physics discussion in the replies that I highly suggest you read. Jofwu and I've discussed other possible relationships between Force and Distance, and there's a bit of a strange one that he came up with a while ago: Allomantic Force ∝ e ^ -d/D where d = distance and D = 16 When the target is right next to the Allomancer, e ^ -d/D approaches 1 and the AF approaches its maximum. When the target approaches an infinite distance away from the Allomancer, e ^ -d/D approaches 0 and the AF approaches 0. This strategy looks very similar to the linear relationship but avoids its icky discontinuity at the max range of the push. I like it a lot. For comparison, you can see all three Force-Distance relationships together here. Edit 2: Following Jofwu's footsteps, I had a conversation with /u/Phantine on reddit and am reconsidering how distance affects the Allomantic Force. I was originally confident in an inverse square relationship between Allomantic Force and the distance between the Allomancer and target, but through testing, a *linear* relationship has better handling and feels more reminiscent of Allomancers' movements in the books. I've added both as options in the game: The Allomantic Force is proportional to the inverse of the square of the distance between the Allomancer and the target When the target is right next to the Allomancer, the Allomantic Force approaches infinity. When the target approaches an infinite distance away from the Allomancy, the Allomantic Force approaches 0. The Allomantic Force decreases linearly with the distance between the Allomancer and the target. When the target is right next to the Allomancer, the Allomantic Force is at its maximum. When the target is at the max range (arbitrarily at 50 meters), the Allomantic Force is 0. I've also added the option to control the strength of your push through two control schemes: The player sets the *percentage* of the maximum possible force they can push with, or The player sets a *constant force* to try to push at, if possible. Edit 1: If you want to play the current build of the game, you can find it here on my GitHub. Aside from that, I've looked back at [8], @digitalbusker's post and see I misunderstood it a bit. I've re-read it and realized that I agree with it much more than I thought I did originally. In one paragraph, they said, This sounds just like the Allomantic Normal Force idea I used in the game. If you push on a target and the target can't move, the target pushes back on you as if there were a long, tangible line between you and the target. In this way, the ANF does work somewhat like an elastic collision. I did some more testing in the game and anything that involved directly manipulating velocities of the target or Allomancer worked poorly. I feel like sticking to forces rather than energy is the right way to go. Table of Contents I: Introduction I-a: My intent I-b: Current game progress & Videos I-c: Referenced forum posts I-d: Definitions II: Force, mass, and acceleration of a push III: Anchors and the pole analogy IV: Math V: Summary & Final points Part I: Introduction Over the summer I’ve been rereading Mistborn and have been thinking about the mechanics of Allomancy. I decided to have a go at recreating the physics of Ironpulling and Steelpushing in the Unity physics/game engine. I don’t intend on actually creating a game to sell (that’d be a bit illegal), so this is mostly an endeavor for personal fun. What follows is my current progress on the game as well as my current thoughts on the math and physics of Pushing and Pulling. Part I-a: My intent My goal is to take what Brandon describes in his books and do my best to create a working model of them in the Unity engine. My purpose in posting this here is to record my thoughts so I can be internally consistent, encourage discussion, and improve the game’s mechanics with your suggestions and criticisms. I don’t expect to perfectly recreate Allomancy as Brandon describes it in the books because there are some things with little connection to real-world physics (such as Feruchemical weight). I’ll try to give the pros and cons for all my decisions. If you disagree, tell me! I’ve been in my own personal bubble while making this, so I’d love some external input. Part I-b: Current game progress & Videos So far, I’ve implemented most of the physics and fundamentals of Ironpulling and Steelpushing. Here are some short videos: The setting: The sandbox I use for testing is based on Luthadel. There are metal poles stuck in haphazardly-placed buildings, and a few windows with metal frames/latches. At the intersection are metal objects of various masses, including coins, ingots, and 16-ton steel blocks. Blue metal lines: When the player (the grey sphere) begins passively burning metal, they see blue metal lines pointing towards nearby metal sources. The wider the line, the heavier the metal, and the brighter the line, the closer the target. Basic pushing/pulling: The player can “target” a metal. They can then push or pull on that metal. They can increase or decrease the strength of the push, as indicated by the wheel near the bottom. They can target multiple metals simultaneously (as indicated by the bright blue number beneath the wheel). Pull targets vs. Push targets: The player has separate targets for pulling (indicated by blue) and pushing (indicated by red). When the player pushes or pulls with specified push targets and pull targets, the player only pushes on the push targets and only pulls on the pull targets. If the player only has pull targets or only has push targets, they can push and pull on any target. Pushing/pulling with coins: The player can throw, drop, and pick up coins. The number in the lower right corner indicates the number of coins in the player’s pouch. Flying around Luthadel: It’s a bit tricky, but the player can fly between buildings by pulling on metal latches and pushing on coins. Some things are still a bit buggy, namely the camera, coin physics, and width of the white part of the blue/red line pointing at a target while pushing. Part I-c: Referenced forum posts Many of the ideas used in the calculations come from the work previous Sharders have done on making sense of Brandon’s magics. Here are some that I used, which I recommend to anyone interested in the physics of Allomancy: When I use specific ideas from these threads, I’ll mark it with a [#]. Other threads I found interesting: Part I-d: Definitions Key statements are italicized. Key terms are written in bold for their first appearance. Push – unless I specify otherwise, I’ll simply say “push” instead of “push/pull” to refer to the math of both steel and iron. It’s a lot easier to read while still means the same thing. All physics and rules of a pull are the same as a push, just in the opposite direction. Target – the metal that an Allomancer is currently pushing on. Coins are often a target. Distance – the distance between an Allomancer and their target. Anchor/anchored – a target is an anchor if it does not move. A lamppost, a coin stuck on the ground, and a metal roof would all be anchors. Note that the metal is the anchor, not the nearby wall/ground/stone. A target is unanchored if it is moving freely with no resistance. A target is partially anchored if it meets some resistance but is not fully anchored (i.e. a coin skidding on the ground). Allomantic Force (AF) – the force that an Allomancer directly exerts on a target while pushing. Equal in magnitude to the force that the target directly exerts on the Allomancer while pushing. The Allomantic force does not change if the target is anchored or unanchored. Allomantic Normal Force (ANF) – the force that is exerted on an Allomancer or target as a result of the opposing target or Allomancer's push or pull by the surrounding ground, walls, etc. I'll discuss this down below. Essentially, it's what makes anchored targets give that extra strength to your push. Now, let's jump into the physics of Allomancy. Part II: Force, mass, and acceleration of a push When Allomancers in the books refer to “weight,” they almost always mean mass. [1] Let’s ignore Feruchemical weight for now. When an Allomancer pushes on a target, the Allomancer exerts a force on the target that is equal and opposite to the force that the target exerts on the Allomancer. It’s F = ma, it’s Newton’s third law, and if anything else were the case, the physics of Mistborn would be far too distant from our world for a good simulation. This explains one of the core features of pushing and pulling: If you push on an object heavier than you, you will accelerate more than it (and vice-versa). You push on a coin out in front of you. The force is the same between you and the coin, but the coin has less mass, so it accelerates more than you. The coin goes flying, but you hardly move. Likewise, heavier objects (like cars) have more mass than you, so you accelerate more than them. The previous statements are most apparent with an Allomancer and target in free-fall or space, where the Allomancer and target (such as a coin) won’t be anchored by anything (such as the ground). When the Allomancer or target are anchored by a wall or the ground, things get complicated. Part III: Anchors and the pole analogy In the books, if an Allomancer is falling through the air, throws a coin downwards, and starts pushing on it, the Allomancer doesn’t feel much while the coin is falling through the air and unanchored. The Allomancer pushes on the coin, but their acceleration from the push is not enough to stop their fall. Once the coin hits the ground and stops moving, the Allomancer suddenly “can get a stronger push” and decelerate more strongly. Here is my interpretation: Pushing against an anchored coin on the ground has a similar effect as holding a long pole and physically pushing against the ground. The Normal Force due to the Allomantic Force (Allomantic Normal Force, or ANF) that the ground/wall/etc. exerts on the target is transferred to the Allomancer. If you held a long vertical pole and pushed down on the ground, the ground would push back on you and the pole. If you tried to push the pole into the ground, the ground would resist, and you could climb upwards relative to the ground. Allomancy mimics this effect. When pushing on the coin, it is like you are physically connected to the coin. If something resists your push, you experience that resistance. It's just like you're literally pushing against the coin with your fists. If the coin's in the air, hardly anything happens. If the coin's on the ground, the ground resists. I drew some free-body diagrams that hopefully help explain what I’m saying. In these, an Allomancer and coin are falling down. The Allomancer is pushing on the coin. Let me discuss two of the other theories as to how Allomancers get stronger pushes from anchored targets: When the coin is airborne, the allomancer is only pushing on the mass of the coin. But when the coin is anchored to the planet, they are also pushing on the mass of Scadrial/the ground around the coin, which causes the Allomancer to accelerate more. [not a quote, but the concept taken from 1] I’ll get into how mass affects the force later in the math section, but I want to now make something clear. With my interpretation, Allomancers push on the mass of metal, not the combined mass of metal and nearby non-metal (the planet). When pushing against an anchored coin, the Allomancer is only indirectly pushing on the ground – they are pushing on the coin, which pushes on the ground, which resists back on the coin, which resists back on the Allomancer – similar to holding a long pole and pushing on the ground. An Allomancer’s strength is the amount of kinetic energy they can add to the system of the coin and allomancer. When the Allomancer pushes on an unanchored target, that kinetic energy is distributed between the two, proportionally to their masses. But, when the target is stationary, their velocity is zero, so all of the kinetic energy is given to the allomancer (and vice-versa). [paraphrased from 8] I like this explanation. Honestly, I may agree with it more than with my own ANF theory. I tried it out, but it was a lot more difficult programming-wise than the ANF idea. Unity has easier force manipulation than energy manipulation, so I framed my theory using that. Energy is just force with extra steps. (See Edit 1) I’ll talk more about the Allomantic Normal Force and partially-anchored targets after the math in Part V. Part IV: Math Now, I’ll introduce the formula that I used to calculate the Allomantic Force. After that, I’ll describe each of the terms in detail. Allomancy is a lot like magnetism, so let’s start by looking at the formula for the magnetic force between two poles. In Allomancy, the “two poles” would be the Allomancer and target. Magnetic Force = Constant * q1 * q2 / r2 Constant – some constant that depends on the medium between the poles. q1and q2 – the magnitudes of the magnetic charges of the poles. r – the distance between the poles. The greater the charges, the greater the force. The greater the distance between the two poles, the weaker the force – and through the inverse square relationship, greater and greater distances cause much weaker and weaker forces. Now, the Allomantic Force: Allomantic Force = A * S * b * c1 * c2 / r2 (See Edit 2/3) A – some constant. This depends on how all pushes and pulls are described in the book and can be increased/decreased for overall stronger/weaker pushes. b – Burn rate. See below. S – Allomantic Strength. See below. c1 and c2 – the Allomantic Charges of the Allomancer and target. r – the distance between the Allomancer and target. Burn rate – the rate at which an allomancer burns their metals. For my purposes, burn rate is a range between 0 and 1, where 0 is “not burning at all” and 1 is “pushing as hard as you can,” possibly without flaring. I bound this to the triggers on a gamepad and to the scroll wheel on a mouse, which allow me to variably control the strength of a push using the burn rate. Allomantic Strength – the most magic-y of the all the components of the force. Some Allomancers are naturally stronger than others, perhaps by sDNA. Allomancers get better with training and experience. These factors get bundled into the Allomancer’s Allomantic Strength. The Allomantic Force is not proportional to the Allomantic Strength (see [3]). Rather, the Allomancer’s maximum burn rate is proportional to the Allomantic Strength. In this way, Allomantic Strength acts as a sort of limiter. Stronger Allomancers must be able to burn more metal faster for a stronger effect. I won’t incorporate this in-game. Allomantic Charge – Analogous to magnetic charge. Contributes to the Allomantic Force. A property of both metals and Allomancers. I recommend now reading [1], which has a very interesting theory on this. I’m not adhering to it completely, though. An Allomancer or target’s Allomantic Charge is a function of its mass. To make the mass relationships of Mistborn work, we need to satisfy a few factors: The more massive a target is, the stronger a push an Allomancer can get off of it. The less massive a target is, the weaker a push an allomancer can get off of it. “[Wax] shot outwards in a grand arc above the city, flying for a good half a minute on the Push off those enormous girders” (AoL ch 1 pg 34) [3]. “…the lamp was a good anchor - lots of metal, firmly attached to the ground - capable of pushing [Wax] quite high” (AoL ch 1 pg 32) [3]. Both of the targets in these quotes are equally anchored, but the girders are much more massive and provide a stronger push. I don’t have any direct quotes, but we know that Allomancers get less of a push from coins than they do from, say, enormous girders. The “heavier” an Allomancer is, the stronger their push. This argument comes from Feruchemical weight, not mass, but it nonetheless impacts Allomancy in the books, so I should bring it up here. While tapping weight, Wax thought, “with this incredible conflux of weight, his ability to Push grew incredible” (AoL) [2]. I can’t quite remember the context or quote, but I recall that one of Kelsier’s surprises about Vin was her Allomantic Strength/Charge was large “for her size,” implying that smaller/less massive Allomancers usually have less charge. It’s symmetrical with the target’s mass impacting the Allomantic Charge. It’s intuitive and makes sense. There should be some soft maximum cap and minimum cap to the force. If an Allomancer pushes off of an absolutely massive multi-ton solid block of gold, they shouldn’t be pushed into the stratosphere. Likewise, coins are very light relative to lampposts and roofs, but they still provide a reasonably strong push. This leads me to the most disgusting part of the math. What exact relationship do the masses have with the force? The relationship can’t be zero. If this were the case, mass would have no effect on the force, which I argued against. Also, an Allomancer could push on a “metal” with a mass of 0 and still get a push, which doesn’t make sense. The relationship can’t be linear. If this were the case, a target 10 times as massive as another would provide 10 times a push as the other, which doesn’t appear to be the case. If an Allomancer pushes first on a 30g coin and then on a 30kg metal block, the Allomancer would receive 1000 times more the force from the block than the coin. In the books, Allomancers push off of girders and roofs which are much heavier than 30kg, but they certainly don’t describe such a massive difference in forces from coins. That’s duralumin-levels of strength. I’ve tried out a lot of relationships. Logs, sum of logs, product of logs, and roots. Eww. My solution was to take the root of the masses of the Allomancer and target. Specifically, the, ah, sixteenth root. It provided a good combination of strong-enough pushes from light coins and weak-enough pushes from very massive targets that felt most similar to the books. The number 16 was arbitrary. I figured I might as well use Scadrial’s base number for legitimacy. If I used a more elegant root (i.e. the square root), coins provided practically no force, and massive targets still pushed to the stratosphere. Higher roots “level the playing field” more than lower roots. c1 = sixteenth root of (m1) c2 = sixteenth root of (m2) m1 – mass of Allomancer m2– mass of target Because of how roots work, we can also say that c1 * c2 = sixteenth root of (m1 * m2). Regarding the maximum to the force that an Allomancer can get from an extremely massive target: The heavier and heavier the target, the less and less the increase in force. No pushes to the stratosphere. I’m not actually sure if this is the case with roots, but it felt like it was: the lighter and lighter the target, the less and less the decrease in force. Coins are very light, but still provide a significant push. In the end, I’m not actually trying to figure out how mass affects the force in the books. I am fairly confident Brandon didn’t consider the exact relationship while writing the books. I’m just finding ways to emulate it in a physics engine. Part V: Summary & Final points And here’s the final, composed formula for the force an Allomancer experiences while pushing: Force on Allomancer = Allomantic Force + Allomantic Normal Force = Allomantic Constant * Burn rate * sixteenth root of (target mass * Allomancer mass) / squared distance between Allomancer and target (See Edit 2/3) + Allomantic Normal Force Burn rate is between 0 and 1. A Burn rate of 1 gives the maximum Allomantic Force. When target mass is 0 or the Allomancer mass is 0, the Allomantic Force is 0. The closer and closer the target is to the Allomancer, the greater and greater the Allomantic Force. Like other normal forces, if the target isn’t fully anchored (e.g. a coin sliding across the ground, or a thin metal rod that bends as you push on it), the Allomantic Normal Force ranges from 0 to the Allomantic Force, depending on how anchored the target is. This means that an Allomancer pushing on a perfectly anchored target will be pushed back with twice the force as a perfectly unanchored target, assuming they have the same distance. This last bit about the distance is key. If an Allomancer is falling through the air and throws down a coin, the coin quickly falls further and further down. The Allomantic Force quickly becomes very small. Only once the Allomancer falls further and is near the coin – now anchored to the ground – does the distance stay small enough for the Allomantic Force to be large enough for a long enough time to scale a building. Friction (and air resistance) can also be a normal force, in this context; any (normal component of a) force that resists the Allomantic Force can be an ANF. Gravity, too, can be an ANF. An allomancer hovering in the air (whose push cancels out gravity) exerts an ANF equal to gravity back to their target. Theoretically, the Allomantic Normal Force could be greater than the Allomantic Force if the target accelerated in the opposite direction of the push. If you pushed (not pulled) on a target, and the target moved towards you (e.g. a very determined Steel Inquisitor, resisting your push and walking towards you), that normal force would push on you harder. This could result in “pushing matches” between Allomancers who try to move towards each other for even stronger pushes. Allomantic Normal Force works both ways. If the Allomancer is anchored (e.g. braced against a wall), the target will experience an Allomantic Normal Force. Other details: There are two main coins in Mistborn: Imperial boxings (gold) and clips (copper or bronze). In real life gold coins are usually around 30 grams, but I’ve experimented with increasing their mass by about 10-100 times for the game. Currently, I’ve kept them as 30g. When pushed with any reasonable force, 30g coins instantly fly off of the screen like bullets. There’s no user feedback that they pushed on that coin, other than, “that coin no longer appears to exist.” If you drop a coin from the air, it is on the ground by the next frame. Coins are sometimes described as behaving like bullets, but I don’t like how that works in the game. With heavier coins, you can see the coin after you push on it, but it still moves very quickly. Another option (which is the one I’m using in the game) is to simply cap their maximum velocity. I’ve left it at around 120m/s, which feels good. That’s about 1/3 the speed of sound. It causes some problems with calculating the Allomantic Normal Force from the target, but those have been resolved with coding (more or less). The image on the coins in the game is taken from Shire Mint. Fun fact: Unity doesn’t let you modify force vectors individually, which makes this a bit hard. You can only add forces/accelerations/velocity changes one at a time, then they are all applied to the object at the end of the frame. Calculating the Allomantic Normal Force is absolutely disgusting. See my code on GitHub, if you’re curious. I hope you all enjoyed the read! Please discuss this and give your opinions on the physics and maths of Allomancy. Specifically, Are there any more elegant relationships between Allomancer/target mass and Allomantic Force that you think I should try? Does anyone have any esoteric knowledge of Unity’s Rigidbody/Force systems that you think could be helpful? Any general ideas for the game? Any suggestions from what you can see in the videos? Any spelling/formatting issues with the post? Thank you.
  4. Recently, I wanted to create a fantasy world setting with two moons. And, of course, because I’m a complete mathochist, I decided to have a theoretically possible solar system in which to create this. This lead down the rabbit hole, and I got to have a long worldbuilding session (actually several) to create this world, with some pretty amazing results. So, I figure, why not go over this whole process on these forums? I’ll go into it in detail, explaining as much as I can, but I’ll leave markings if you don’t want to go through all the hard work. IMPORTANT NOTE: Whenever I mention something like ‘full moon’ or ‘equinox’, I’m not refer to the day, I’m referring to the precise position which occurs in an instant. Keep this in mind. WARNING! GEOMETRY AHEAD! SKIP TO WHERE THERE’S MORE CAPITAL LETTERS TO AVOID! Earth has one moon, but, like all orbiting bodies it follows very specific rules, known as Keplerian geometry. There are a few rules to Keplerian geometry, but (for now) we’re just interested in the one which states that all orbiting bodies orbit in an ellipse with two foci. All planets must have the star they’re orbiting around as a focus point, consequently, all moons have the planet they’re orbiting as a focus point. That’s good. All Kelplerian orbits have 5 points known as Lagrangian points. These are fixed points in which objects can be placed to have stable orbits. In relation to the Earth and its Moon, they are as follows: L1 is between the Moon and Earth. L2 is on the far side of the Moon, lining up with the Earth (though not with the Sun, because the Moon orbits the Earth). L3 is the far side of the Moon’s orbit. L4 and L5 are 60 degrees off in the orbit, ahead and behind respectively. (Yes, L4 and L5 are slightly more complicated than that, but that isn’t needed now). I do know (some of) the physics behind it, but that’s a bit off-topic right now. So, it seems that, to have two Moons, we just have to put a Moon on the L3 point, right? Wrong. Because L1, L2, L3 are all unstable points. Can’t put stuff of any decent size mass there. I mean, theoretically, you might be able to put very small mass objects in L3, (like, say, an artificial satellite) but we’d have to resort to magic rock to have a Moon-sized object. So that’s out. We can put a Moon in the L4/5 spot, but I’d rather avoid that because I like the thematic idea of opposite Moons. So, suppose we avoid Lagrangian points, and just have two Moons in the same orbit, opposite each other. Does that work? Yes. And no. The L3 points aren’t enough to keep it in balance, so, (as best as I can figure, and I’m not an astrophysicists) it would need to be perfect placed to avoid them accelerating towards each other due to gravitational forces. A solution, sure, but it’s inelegant and isn’t likely to ever occur naturally. Instead, I decided to follow the binary approach, as in, ‘binary star system’. Binary stars orbit each other (oddly enough) sharing one focus point, while having the other one opposite each other. And, since the Earth is a focus point, we can have two moons orbiting it similar to a binary star system’s. Solved! END OF GEOMETRY SECTION! Long story short, we can two moons orbiting a planet opposite each other. We’re going to assume that the orbital period is exactly 28 days (synodic orbit), because it makes my life easier. (You’ll notice I’m about to make a lot of these assumptions) Now, I could go through the complete lunar calendar with respective positions, but seems like work which doesn’t involve math or writing, so instead, I’ll just list a quick set of rules to follow. 1. There will always be a total of a full moon, if you add the two moons together. 2. Draw the two moons in orbit around the planet. Draw a line between them so it looks like a ‘divide’ symbol. The respective moons can only be seen by people from their side of the planet, both can be seen while on the line itself. The moons can only be seen at night, though. 3. The moon which can only be seen in the beginning of the night is the waxing moon. The moon which is seen after midnight is waning. 4. Once every two weeks is full moon, swapping moons. Once every other series of two weeks is perfect half-moons, swapping waning and waxing Are we done? Hah! As I said, I’m a mathochist, and, what’s more, I’m a Julian-loving mathochist at that. I haven’t even started. Because now that we’ve gotten the moon out of the way, let’s talk about the planet. MORE GEOMETRY! IT’S FUN, I PROMISE! Kepler’s Law of Orbital Motion states that planets have a constant area speed. In other words, time it takes to cover a portion of the orbit such that it has area n between the start point, end point, and the sun (as a triangle, of sorts) is the same time it takes to cover any other points with the same area. Or, bluntly, area = time. (Not entirely right, but right enough for this discussion.) Equinoxes and solstices are caused by the tilt in the Earth’s spin which is completely independent from the elliptical orbit. Equinoxes are when the tilt is in a tangent to the Earth’s orbit to the Sun, solstices are when it is either pointing towards the Sun or away from it. Equinoxes have equal 12 hour day/night, solstices have longest day or longest night (summer, winter respectively). This is important because of the equinoxes and the solstices. Since these occur at 90 degrees from each other, we can adjust the time between solstices and equinoxes by moving the free focus point around and mucking around with length and width of the ellipse. (If you want to draw a diagram, draw a plus. The center of the plus is the sun. Draw an ellipse, with one focus being the center of the plus. Where the lines of the plus and the ellipse lines meet are the solstices and equinoxes.) Time adjustment to is possible, but it is complicated, so let’s move on. I’m just going to assume all the finite little adjustments I’m about to mention is possible because I think it is and because even I have my limits when it comes to this stuff. Calendar math is just a hobby. AND WE’RE ALL DONE WITH GEOMETRY! COME BACK, PLEASE! Now, this section requires some math. You can’t skip it, because this is necessary for orbital calculations. Promise. (Well, okay, you can skip to the last three paragraphs, but come on! It’s calendar math. Why would you want to skip it?) (No seriously. Don’t skip if you want to learn how to do this yourself.) So, let’s say we make the year 364 days, exactly 6 hours. (cough can’t imagine why I’d do that cough) That means (aside from needing a leap year precisely every four years, but see the note on that later) the solstice would move six hours, and we’d have a total of 13 28-day months. What does this mean? Well, let’s assume the winter solstice occur at precisely 1200 hours the first year. At Year+1, it will occur at precisely 1800 hours. At Year+2, it will occur at 2400, Year+3 0600, Year+4 back to 1200 and the cycle repeats. Same for the others. Now it’s easy to see why time adjustment between the equinoxes and solstices are necessary. There are 13 lunar months. If there is an equal amount of time between solstices + equinoxes, only one solstice/equinox can fall out during a full moon. If, say, the distance between them is 5-3-2-3 months (this is possible), they can all occur during a full moon, they just have variable time lengths between them. (In fact, the Earth’s distance between equinoxes is slightly off.) All’s well that ends well? Ha! Because, remember, the equinox progresses 6 hours per year (assuming the year cycle we established. Remember, you can whip up any numbers to your own liking) So, after a perfect solstice / full moon overlap, in 4 years, the full moon will have moved 1 day forward. In 28 years the full moon will have moved 1 week forward, and the winter equinox will now occur during perfect half-moons. In 56 years, we’ll be back at full moon, but with the other moon (remember, this planet has two moons) and in 112 years, it’ll be back where it started. All-in-all, I now have a 112-year lunar cycle calendar to use for my fantasy world. But wait! I was using the winter solstice in conjunction with the full moon as an example but we still have the summer solstice, vernal equinox, and autumnal equinox to use within our 112-year cycle. Can we have a system which only allows one full moon per year to coincide with one of the four? Yes, the easiest way to do this is to add a six-hour gap in the cycles, giving us 5-3-2-3, except each one also has six hours in addition to the months, but giving either the 5 or 2 an extra 12 hours after subtracting a day. (The math works, trust me on this. There may be other ways, but this is my way.) SUMMARY: So, every four years, the winter solstice, vernal equinox, summer solstice, autumnal equinox all swap between full moons, but these series of four years only occur every 28 years, but every cycle of 28 swaps between one of four options, (Full moon A, equal moons waning A, waxing B; Full moon B; equal moons waxing A, waning B; in that order unless I made a mistake) giving us a full cycle of 112 years total. Now, how does this cycle work when we have a specific 13-month calendar? Evil laugh. I thought you’d never ask. Since every four years adds a day, the calendar is moved one month every 112 years, if we don’t add leap days (which I don’t intend to). Which means, when a winter solstice occurs during a full moon during a specific month, that will not happen again for 1456 years. See? Math and world-building is fun. And, for those who remember me, I'm back. Nice to be here again.
  5. Simply awesome.... I think we need a separate thread so everyone can get all their comments and math jokes out, and leave the ch 13-15 reaction thread for reactions. Personally I'm waiting to preorder my "Want to divide by zero?" t-shirt from brandon's site
  6. Here are a couple of calculations I did about Roshar. The necessary variables (gravitational constant, radius) are from the AU essay. DISCLAIMER: I have little experience with astronomy, and these calculations may be wrong. Please submit any corrections, to improve the data. Roshar's mass: Gravitational constant = 70% of earth Radius = 90% of earth Mr = mass Roshar m*g=(G*Mr*m)/r^2 m*g*r^2=G*Mr*m g*r^2=G*Mr Mr=(g*r^2)/G Mr=((9.81*0.7)*(6.371*10^6*0.9)^2)/(6.673*10^-11) Mr=(6.867*3.288*10^13)/(6.673*10^-11) Mr=(2.258*10^14)/(6.673*10^-11) Mr=3.383*10^24 kg To calculate Roshar's orbit, and the mass of the sun I had to do something different. As I couldn't find any data on it on the internet I used the AU starmap. Here, the color of the sun is lighter than that of our sun, making it seem that it is of a higher spectral class ( I then took the spectral classes above that of the sun (F till O) and created a tool that takes the highest and lowest luminosity, and then uses that to calculate the habitable zones. I then calculate what the mass of the star need to be to make Roshar have its period of 1.1 years and still fall in the habitable zone. the program repeats this till the mass of the star is also within the right class. The results are as followed: If you want to use the tool yourself, I attached the python file here: This shows that Roshar's sun would probably have a mass of around 1.4 solar masses. this would mean that the semi-major axis of Roshar is: r=((G*M*T^2)/(4*pi^2))^(1/3) r=(((6.673*10^-11)*(2.8*10^30)*(3.15*10^7)^2)/(4*pi^2))^(1/3) r=((1.85*10^35)/(4*pi^2))^(1/3) r=(4.69*10^33)^(1/3) r=1.67*10^11 meter r=1.12 au (astronomical unit, earth's distance from the sun) I would also appreciate it if someone with more knowledge of astronomy looked over my calculations and my code, as I don't have much knowledge on the subject, and it is fairly possible I have made some mistakes.
  7. I assume Every shard can combine with the regular 16 metals to form 16 new alomantic alloys (as can every shard combination because harmony and harmonium) then there are a total 1,048,576 possible alomantic metals and powers if all sixteen shards and their combinations are used. This includes the known god metals. this is based on the facts that: It has been confirmed by Brandon that what ruin is to atium, Honor is to shardblades Based on the formula File:Https:// Where N is the number of shards and are can equal any whole number between 1 and 16 (sixteen shards) plus the additional non god metals as one more combination, the following determines the maximum number of allomantic alloys (65535 + 1) * 16 = 1,048,576
  8. Last May, Tempus posted something that he/she called "Shardic Number Theory." Tempus included a section that discussed Bavadin (now known as Autonomy), the shard on Taldain, but had to censor most of the White Sand-Specific words. Here is the section: Bavadin - Five, Eight, Nine We don't know much about Bavadin, but there are a few options. There are five shshshshsh, and a shshshshsh can have five shshshshsh. The religious texts on shshshshsh are five hundred years old. There are eight shshshshsh, who elect eight shshshshsh, and shshshshsh spent eight years training. The shshshshsh religion sends eight shshshshsh at shshshshsh per day. There are also nine ranks of shshshshsh, nine people in shshshshsh's expedition, a maximum of nine shshsh without over-shshshshsh, and nine shshshshsh if you count the beggars. This paragraph brought to you by the Librarians. Now that we have a forum on which we can talk about white sand, who wants to fill this in? EDIT - I think that it was actually May 2014.