from visual import *

#Constants
G = 6.7e-11
day = 24*60*60
year = 365*day
pscale = 1e11/1e29/3
fscale = 1e11/1e22/4

#Objects
Sun = sphere(pos=vector(0,0,0), radius=1e10, color=color.yellow)
Earth = sphere(pos=vector(1.5e11,0,0), radius = 5e9, color=color.cyan)
scene.autoscale = False

parr = arrow(color=color.red)
farr = arrow(color=color.green)

Sun.m = 2e30
Earth.m = 6e24

#Initial values
Sun.p= vector(0,0,0)
Earth.p = Earth.m*vector(0,2*pi*Earth.pos.x/year,0)
Earth.trail=curve(color=Earth.color)
Earth.trail.append(pos=Earth.pos)

deltat = day
t=0

#Loop for repetitive calculations
while True: # t < year:
    rate(100)
    r = Earth.pos - Sun.pos
    rmag = mag(r)
    rhat = r/rmag
    Fnet = (-G*Earth.m*Sun.m/rmag**2)*rhat

    Earth.p = Earth.p + Fnet*deltat
    Earth.pos = Earth.pos+Earth.p/Earth.m*deltat
    Earth.trail.append(pos=Earth.pos)
    parr.pos = Earth.pos
    parr.axis = pscale*Earth.p
    farr.pos = Earth.pos
    farr.axis = fscale*Fnet
    t = t + deltat