kenod Posted January 31, 2017 Report Share Posted January 31, 2017 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 (https://en.wikipedia.org/wiki/Stellar_classification#Harvard_spectral_classification). 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: Spoiler Initiation values for F class star Results: Initiation values for A class star: Results: B and O class stars also can't find a solutions. If you want to use the tool yourself, I attached the python file here: stellar_mass.py. 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. 9 Link to comment Share on other sites More sharing options...
king of nowhere Posted January 31, 2017 Report Share Posted January 31, 2017 I don't know about programming, but all the data seems fine. roshar is about 55% the mass of earth, which makes sense for a slightly smaller and less dense planet. its sun is a bit bigger, hence the longest year. I wouldn't expect different values Link to comment Share on other sites More sharing options...
Argent Posted January 31, 2017 Report Share Posted January 31, 2017 Maybe @PeterAhlstrom can drop in this thread and look over your numbers, my money is that if anyone knows, it will be him. Link to comment Share on other sites More sharing options...
kenod Posted January 31, 2017 Author Report Share Posted January 31, 2017 I hope so, I think that my mass calculations should be right, but I'm getting the impression that something weird is going on with the solar calculations. I have considered that Roshar doesn't use the rotation around the sun as indicator for years, as they have the weeping. Link to comment Share on other sites More sharing options...
Jofwu Posted January 31, 2017 Report Share Posted January 31, 2017 5 minutes ago, kenod said: I have considered that Roshar doesn't use the rotation around the sun as indicator for years, as they have the weeping. I doubt that's the case. It's always referred to simply as a "year" without qualification, and that's the basic definition for a year. They don't have seasons to measure by, but they do have the stars. I expect that the Weepings are simply in sync with the revolution around the sun- either for natural reasons or otherwise. Link to comment Share on other sites More sharing options...
BlackYeti Posted January 31, 2017 Report Share Posted January 31, 2017 3 hours ago, kenod said: Radius = 90% of earth Careful here, it actually says that the size is 0.9, and size is an ambiguous term. It could mean radius (and I've in fact based calculations on that assumption in the past since it's convenient ), but it could also mean volume, or even mass. To be honest, I actually think that the most likely meaning is volume since: 1) it's what's most commonly meant by size, and 2) it leads to the most realistic numbers, at least in the calculations that I've done. Link to comment Share on other sites More sharing options...
Yezrien Posted January 31, 2017 Report Share Posted January 31, 2017 I know this isn't a helpful comment, but Roshar might not be playing by the standard rules, astrophysically speaking. This is the planet of greatshells and skyeels, which can only exist because they're bonded with spren that bend the laws of physics. The planet itself, and even the star, might be doing something similar. If you consider all the different surges that Radiants can manipulate, almost any aspect of the system could be more magical than natural. Maybe the star is too small to exert sufficient gravity, so the planets are held in their orbits with giant Lashings. Maybe the sunlight is too weak to support a biosphere, so all Rosharan plant-life is dependent on Cultivation, or Highstorms. Link to comment Share on other sites More sharing options...
king of nowhere Posted January 31, 2017 Report Share Posted January 31, 2017 59 minutes ago, BlackYeti said: Careful here, it actually says that the size is 0.9, and size is an ambiguous term. It could mean radius (and I've in fact based calculations on that assumption in the past since it's convenient ), but it could also mean volume, or even mass. To be honest, I actually think that the most likely meaning is volume since: 1) it's what's most commonly meant by size, and 2) it leads to the most realistic numbers, at least in the calculations that I've done. What do you mean by, the most realistic numbers? They are all pretty realistic. By assuming that 0.9 is the radius, you get 0.55 earths mass, and a density of 4.2 g/cm^3, around 75% the value for earth, mercury and venus, but slightly bigger than that of mars. It's a perfectly realistic density for a rocky planet. If, on the other hand, you assume 0.9 is the volume, then you get a radius of 0.965 earth radii, which after all the calculation leads to 0.65 earth's mass, which leads to 72% the density for earth - since the planet is more massive than in the previous calculation, but also bigger. The point is, the two values are almost identical, and they fall comfortably within the extremes of the sample of rocky planets we know. How can one be more realistic than the other? Link to comment Share on other sites More sharing options...
Krandacth Posted January 31, 2017 Report Share Posted January 31, 2017 Also, using the OPs figures and data regarding luminosity/habitable zones and planet density, we end up with a year of approximately 1.1 au, which is the stated length of a Rosharan year. I would say it all adds up nicely :-) Link to comment Share on other sites More sharing options...
Argent Posted January 31, 2017 Report Share Posted January 31, 2017 6 minutes ago, Krandacth said: we end up with a year of approximately 1.1 au AU is a unit for distance, but I know what you mean. Link to comment Share on other sites More sharing options...
Krandacth Posted January 31, 2017 Report Share Posted January 31, 2017 Oh, of course. My high school physics deserted me for a while there :S being on a train and just glancing over the equation's doesn't help either! Link to comment Share on other sites More sharing options...
BlackYeti Posted January 31, 2017 Report Share Posted January 31, 2017 Just now, king of nowhere said: What do you mean by, the most realistic numbers? They are all pretty realistic. By assuming that 0.9 is the radius, you get 0.55 earths mass, and a density of 4.2 g/cm^3, around 75% the value for earth, mercury and venus, but slightly bigger than that of mars. It's a perfectly realistic density for a rocky planet. If, on the other hand, you assume 0.9 is the volume, then you get a radius of 0.965 earth radii, which after all the calculation leads to 0.65 earth's mass, which leads to 72% the density for earth - since the planet is more massive than in the previous calculation, but also bigger. The point is, the two values are almost identical, and they fall comfortably within the extremes of the sample of rocky planets we know. How can one be more realistic than the other? I'm sorry if I wasn't clear, but I haven't had time to go through @kenod's calculations and was basing that solely on calculations that I've done in the past, specifically with regards to the planet Sel. Also I didn't mean to imply that it couldn't be the radius (in fact I believe that I stated up front that it could be), only that I think it more likely that it is volume. Elantris spoilers: Spoiler Incidentally, the calculations I was referring to were pertaining to Sel's surface area, which, assuming size to be equal to radius, would have to be well over twice the size of Earth's. Now whilst this isn't outside the realm of possibility, it's larger than I've been imagining, especially given how Brandon reduced the number that Raoden used with Aon Tia to get to Teod in the 10th Anniversary version since the planet would be too large otherwise. Link to comment Share on other sites More sharing options...
UpLifted Posted January 31, 2017 Report Share Posted January 31, 2017 Sometimes I think I'm way too obsessed with the Cosmere... then I come across threads like this and realize that I could be way worse... 5 Link to comment Share on other sites More sharing options...
Argent Posted January 31, 2017 Report Share Posted January 31, 2017 33 minutes ago, UpLifted said: Sometimes I think I'm way too obsessed with the Cosmere... then I come across threads like this and realize that I could be way worse... Oh, buddy. Go look at the 80 pages Easter egg hunt on the map of Roshar. Or the translation of the Alethi women's script and glyph pairs. This is timid in comparison 5 Link to comment Share on other sites More sharing options...
kenod Posted January 31, 2017 Author Report Share Posted January 31, 2017 1 hour ago, UpLifted said: Sometimes I think I'm way too obsessed with the Cosmere... then I come across threads like this and realize that I could be way worse... It wasn't actually that hard. The mass calculation was fairly easy, when I found the data in AU. The star calculations were harder, but when I found the right calculations online writing the tool was easy. Link to comment Share on other sites More sharing options...
king of nowhere Posted February 1, 2017 Report Share Posted February 1, 2017 I am more obsessed with science in general, and astrophysics in particular, than with the cosmere. But look! Here I have both at once! Link to comment Share on other sites More sharing options...
The One Who Connects Posted February 1, 2017 Report Share Posted February 1, 2017 (edited) 5 hours ago, UpLifted said: Sometimes I think I'm way too obsessed with the Cosmere... then I come across threads like this and realize that I could be way worse... Take a day off to look though all 130some odd pages 156 pages of topics in Stormlight Archive Subforum like I did. It's not the same type of obsession, but... Edited February 1, 2017 by The One Who Connects page numbers 1 Link to comment Share on other sites More sharing options...
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