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January 25, 2015 05:15
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there are 5 points in the Sun-Earth system where gravitational and centrifugal forces cancel
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#!/usr/bin/env python | |
#coding:utf8 | |
import numpy as np | |
#Mearth, Msun = 5.97e24, 1.98e30 ## <-- these are realistic | |
Mearth, Msun = 1.97e29, 1.98e30 ## <-- unrealistic, but better for visualisation | |
earth_sun_dist = 149e9 | |
Xsun = - earth_sun_dist * (Mearth/Msun) ## Sun center distance to the center-of-mass | |
Xearth = earth_sun_dist * (1 - Mearth/Msun) ## Earth center distance to the center-of-mass | |
kappa = 6.67e-11 ## Gravitational constant | |
year = 365.25*24*60*60 ## Rotation period [seconds] | |
## Generate the points in the space (takes a second) | |
xaxis, yaxis = np.linspace(-300e9, 300e9, 1000), np.linspace(-300e9, 300e9, 1000) | |
x,y = np.meshgrid(xaxis,yaxis) | |
## Centrifugal force | |
rC = (x**2+y**2)**.5 | |
FC = (2*np.pi / year)**2 * rC | |
FCx = FC * (x/rC) | |
FCy = FC * (y/rC) | |
## Gravity of Sun | |
rS = ((x-Xsun)**2+y**2)**.5 | |
FS = -kappa * Msun / (rS**2) | |
FSx = FS * (x-Xsun)/rS | |
FSy = FS * y/rS | |
## Gravity of Earth | |
rE = ((x-Xearth)**2+y**2)**.5 | |
FE = -kappa * Mearth / (rE**2) | |
FEx = FE * (x-Xearth)/rE | |
FEy = FE * y/rE | |
## All three forces together | |
Fax = FCx+FSx+FEx | |
Fay = FCy+FSy+FEy | |
Fa = (Fax**2+Fay**2)**.5 | |
import matplotlib.pyplot as plt | |
d = 15 # decimation factor | |
## Plot the magnitude of the force: | |
plt.contourf(xaxis, yaxis, np.log10(Fa), levels=np.linspace(-4, 0), extend='both') | |
## ... and its direction: | |
plt.quiver(x[::d, ::d],y[::d, ::d],Fax[::d, ::d]/Fa[::d, ::d], Fay[::d, ::d]/Fa[::d, ::d]) | |
plt.show() # plt.savefig("output.png") |
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