Roshar's Sun

[kenod]

Is there any information on the sun of Roshar? I'm running some calculations and I need either Roshar's semi-major axis or the sun's mass. The map in AU gives me the idea that it's a class B or O star, but that only means that the mass is more then 2.1 solar masses, nothing else.

EDIT: Seeing the size of taldain's larger sun in AU I'm guessing that Roshar's sun is a class B star, probably a smaller one. Also comparing the sizes between the other stars I'm guessing it's around 3 or 4 solar masses.

EDIT 2: Seeing that the light of Sel's sun and scandrial's sun seem to be around class F and G, which puts them between 0.8 and 1.4 solar masses. comparing the sizes of the stars afterwards in the maps it seems to put Roshar's sun around 3 solar masses.

Edited December 21, 2016 by kenod
more info

[Just another guyn he/him]

I looked around the coppermind, and haven't found anything. When you can, try making an article about it.

[Argent he/him]

What calculations are you running? It's possible that we know of a WoB that's relevant to your research.

[kenod]

I was running calculations on Roshar's orbit, and the mass and class of it's sun. I used a different way to get the data, the results are here:

 

[Complexityspren]

On 12/21/2016 at 4:17 AM, kenod said:

EDIT: Seeing the size of taldain's larger sun in AU I'm guessing that Roshar's sun is a class B star, probably a smaller one. Also comparing the sizes between the other stars I'm guessing it's around 3 or 4 solar masses.

EDIT 2: Seeing that the light of Sel's sun and scandrial's sun seem to be around class F and G, which puts them between 0.8 and 1.4 solar masses. comparing the sizes of the stars afterwards in the maps it seems to put Roshar's sun around 3 solar masses.

Are the AU pictures to scale?

[Farnsworth]

I really doubt they are to scale since Threnody's sun would then be smaller than Purity.

Edited May 18, 2017 by Figberts

[kenod]

They aren't, if you follow the link I posted you'll see that with a sun of the mass of my early estimates the distance from the sun where the orbital period is 1.1 earth years wouldn't fall inside of the habitable zone.

[kenod]

On 27/06/2017 at 4:15 AM, Shadows4Silence said:

@kenod Question... Are you an astronomer... Cause that's some deep math dude. Way to go!

Your humble servant...

Shadows4Silence

Actually, it's just highschool physics and self study.

[DocHoliday he/him]

10 hours ago, kenod said:

Actually, it's just highschool physics and self study.

Kudos regardless.

Sadly, the solar map in Arcanum Unbound is not a scale reference, but an artistic rendition.

[king of nowhere]

roshar's sun must be pretty similar to our. We can make some calculations under the assumption that it has the same temperature and density of our own sun (which may lead to an inaccuracy or maybe 20 or 30%).

Given our sun of radius r and mass M around which orbits earth at a radius R in a time y:

we know roshar orbits in time 1.1 y, and that it has a similar temperature to earth: this temperature condition poses a condition for orbital radius: rR/r=RR/R. that's because the amount of irradiated light is proportional to the sun's surface area, so to r^2, and the amount of it that the planet receives is inversely proportional to the surface of the sphere with radius equal to its orbit, so to R^2.

So using the equation for orbital period y=2 π  √ (R^3/ GM ), valid for earth, for roshar we have 1.1 y=2 π  √ (RR^3/ GMR ) and MR=M(rR/r)^3 and rR/r=RR/R, which are three equations with three unknowns (MR, rR/r and RR/R), a textbook example of equation system. the equation itself is unfortunately a bit less of a textbook example, but after some calculations, I reach the point where I get rR/r=1.06 RR/R, which contradicts my system. I can only take it to mean that if you increase linearly the radius of a star and the orbital radius, the orbital period will stay the same. Yes, I can now see clearly that if I double both the radius of the star and the radius of the orbit, the mass will increase at the cube, so I will have ((2*R)^3/ G(2^3)M ) (EDIT: I wrote the formula wrong) and the orbital period will remain the same.

Which proves that with my approximated assumptions you can't solve the relevant equations. You need to assume that the sun is a bit hotter, or maybe the planet has a slightly different albedo or greenhouse effect.

Still, roshar sun's mass and roshar's orbital radius can't be more than minus/plus 20% compared to earth.

Edited June 30, 2017 by king of nowhere