Rebecca Harbison <stareyes at whimsical-dragon.net> Sent by: dragaera-bounces at dragaera.info 04/06/06 01:24 PM To Dragaera <dragaera at dragaera.info> cc Subject Re: Speculative Planetary Statistics for Dragaera (Math help?) >All the math checks out. One thing I noticed is that the axial tilt >is rather higher than Earth's -- and I don't recall seasons on >Dragaera seeming any more severe than those on Earth (hard to >compare, though). I think the spectral type of Dragaera's sun would >be a bit later, maybe a G5 or so. I wonder if the lack of seasonal extremes could be accounted for by an extreme orbital eccentricity that brings the planet much closer to the sun during the winter period of the northern hemisphere? This would moderate the effect of the axial tilt, at least in the north. The southern hemisphere would then receive exceptionally hot summers, and brutally cold winters--but since we don't know what is going on in the southern hemisphere of Dragaera, it's possible this region isn't even inhabited, so that it isn't a problem for anyone. I suppose the other explanation is that warm and cold water currents simply moderate the effects of the seasons on Dragaera to a greater degree than they do on Earth. >You can find the orbital distance by using Kepler's Third Law: a^3 = >M*P^2/Msun, with a being the average distance from planet to star in >astronomical units (the Earth-Sun distance being one AU), P being the >period in years, M being the star's mass, and Msun being the Sun's >mass. The planet's mass actually doesn't matter, since it's so small >compared to the star's. > > You can get an average velocity by just taking the orbit's >circumference, and divide by the period. For a more exact >calculation, you can use the vis viva equation: > >v = (G * M * (2/r - 1/a)) ^ 0.5, G being Newton's Gravitational >constant, and r being the planet's current distance from its star. > >Most useful are the maximum velocity vmax = (G * M /(a(1-e)) ^ 0.5 >and minimum velocity vmin = (G * M /(a(1+e)) ^ 0.5, with e being the >eccentricity. > >Any other useful equations you need? Those are precisely what I needed, thanks! Majikjon