Planetary Motion Simulation

kprov · (This post was last modified: Nov-29-2017, 09:30 PM by kprov.)

I am required to plot the orbits of the planets around the sun. So far I have been able to plot the circular orbits from my code below. However, I am not sure how to manipulate this to make the orbits their real-life elliptical shape. I have all the eccentricity values for the planets but don't know where they fit into my code (if at all?).

Eccentricities:
Mercury = 0.205
Venus = 0.007
Earth = 0.017
Mars = 0.094
Jupiter = 0.049
Saturn = 0.057
Uranus = 0.046
Neptune = 0.011

        
          
          
              
              #--------------------------PLANETARY MOTION--------------------------#
 
#Gravitation is a conservative fore: E = T + V
#The total energy of the system can be expressed as two coupled 1st order ODEs:
 
#dr/dt = v              Where v is the velocity
#dv/dt = F/m            Where F is the force and m is the mass
#F = (G*m1*m2)/(r**2)   m1 and m2 are the mass of the sun and mars respectively
 
#Import necessary libraries:
import numpy as np
import matplotlib.pyplot as plt
 
#Radii of all planets in Astronomical Units:
rMer = 0.387                # Radius of Mercury in AU
rVen = 0.723                # Radius of Venus in AU
rEar = 1.00                 # Radius of Earth in AU
rMar = 1.524                # Radius of Mars in AU
rJup = 5.203                # Radius of Jupiter in AU
rSat = 9.537                # Radius of Saturn in AU
rUra = 19.191               # Radius of Uranus in AU
rNep = 30.069               # Radius of Neptune in AU
 
 
 
#----------INNER PLANETS (Mercury-->Mars)----------#         
 
#Set parameters:
N = 687                     # Mars days in a year
dt = 1.00/N                 # Time Step: Fractions of a year - 1 Mars day (i.e. 1/687)
mu = 4 * np.pi**2           # mu=4pi^2 is the Gravitational Parameter: mu = GM where G=6.67e-11 is the Universal Gravitational Constant and M is the mass of the body
 
 
#-----EARTH-----#
 
#Create an array, for all variables, of size N with all entries equal to zero:
xEar = np.zeros((N,))
yEar = np.zeros((N,))
vxEar = np.zeros((N,))
vyEar = np.zeros((N,))
 
# Initial Conditions:
xEar[0] = rEar                   # (x0 = r, y0 = 0) in AU
vyEar[0] = np.sqrt(mu/rEar)      # (vx0 = 0, v_y0 = sqrt(mu/r)) AU/yr
 
#Implement Verlet Algorithm:
for k in range(0,N-1):
    vxEar[k+1] = vxEar[k] - (mu*xEar[k]) / (rEar**3)*dt
    xEar [k+1] = xEar[k] + vxEar[k+1]*dt
    vyEar[k+1] = vyEar[k] - (mu*yEar[k]) / (rEar**3)*dt
    yEar [k+1] = yEar[k] + vyEar[k+1]*dt
 
#Plot:
plt.plot(xEar, yEar, 'go')
plt.title ('Circular Orbit of Earth')
plt.xlabel ('x')
plt.ylabel ('y')
plt.axis('equal')
plt.show()
 
#-----MERCURY-----#
 
#Create an array, for all variables, of size N with all entries equal to zero:
xMer = np.zeros((N,))
yMer = np.zeros((N,))
vxMer = np.zeros((N,))
vyMer = np.zeros((N,))
 
# Initial Conditions:
xMer[0] = rMer                   # (x0 = r, y0 = 0) in AU
vyMer[0] = np.sqrt(mu/rMer)      # (v_x0 = 0, v_y0 = sqrt(mu/r)) AU/yr
 
#Implement Verlet Algorithm:
for k in range(0,N-1):
    vxMer[k+1] = vxMer[k] - (mu*xMer[k]) / (rMer**3)*dt
    xMer[k+1] = xMer[k] + vxMer[k+1]*dt
    vyMer[k+1] = vyMer[k] - (mu*yMer[k]) / (rMer**3)*dt
    yMer[k+1] = yMer[k] + vyMer[k+1]*dt
 
 
#-----VENUS-----#
 
#Create an array, for all variables, of size N with all entries equal to zero:
xVen = np.zeros((N,))
yVen = np.zeros((N,))
vxVen = np.zeros((N,))
vyVen = np.zeros((N,))
 
# Initial Conditions:
xVen[0] = rVen                   # (x0 = r, y0 = 0) in AU
vyVen[0] = np.sqrt(mu/rVen)      # (vx0 = 0, vy0 = sqrt(mu/r)) AU/yr
 
#Implement Verlet Algorithm:
for k in range(0,N-1):
    vxVen[k+1] = vxVen[k] - (mu*xVen[k]) / (rVen**3)*dt
    xVen[k+1] = xVen[k] + vxVen[k+1]*dt
    vyVen[k+1] = vyVen[k] - (mu*yVen[k]) / (rVen**3)*dt
    yVen[k+1] = yVen[k] + vyVen[k+1]*dt
 
 
#-----MARS-----#
 
#Create an array, for all variables, of size N with all entries equal to zero:
xMar = np.zeros((N,))
yMar = np.zeros((N,))
vxMar = np.zeros((N,))
vyMar = np.zeros((N,))
 
# Initial Conditions:
xMar[0] = rMar                   # (x0 = r, y0 = 0) in AU
vyMar[0] = np.sqrt(mu/rMar)      # (vx0 = 0, vy0 = sqrt(mu/r)) AU/yr
 
#Implement Verlet Algorithm:
for k in range(0,N-1):
    vxMar[k+1] = vxMar[k] - (mu*xMar[k]) / (rMar**3)*dt
    xMar[k+1] = xMar[k] + vxMar[k+1]*dt
    vyMar[k+1] = vyMar[k] - (mu*yMar[k]) / (rMar**3)*dt
    yMar[k+1] = yMar[k] + vyMar[k+1]*dt
 
#Plot Inner Planets:
plt.plot(xMer, yMer, 'ro', xVen, yVen, 'yo', xEar, yEar, 'go', xMar, yMar, 'bo')
plt.scatter(0,0, 'r')
plt.title ('Circular Orbits of Inner Planets')
plt.xlabel ('x')
plt.ylabel ('y')
plt.axis('equal')
plt.show()
 
 
 
#----------OUTER PLANETS (Jupiter-->Neptune)----------#         
 
#Set parameters:
N = 59800                   # Neptune days in a year
dt = 1.00/N                 # Time Step: Fractions of a year - 1 Neptune day (i.e. 1/687)
mu = 4 * np.pi**2           # mu=4pi^2 is the Gravitational Parameter: mu = GM where G=6.67e-11 is the Universal Gravitational Constant and M is the mass of the body
 
 
 
#-----JUPITER-----#
 
#Create an array, for all variables, of size N with all entries equal to zero:
xJup = np.zeros((N,))
yJup = np.zeros((N,))
vxJup = np.zeros((N,))
vyJup = np.zeros((N,))
 
# Initial Conditions:
xJup[0] = rJup                   # (x0 = r, y0 = 0) in AU
vyJup[0] = np.sqrt(mu/rJup)      # (vx0 = 0, vy0 = sqrt(mu/r)) AU/yr
 
#Implement Verlet Algorithm:
for k in range(0,N-1):
    vxJup[k+1] = vxJup[k] - (mu*xJup[k]) / (rJup**3)*dt
    xJup[k+1] = xJup[k] + vxJup[k+1]*dt
    vyJup[k+1] = vyJup[k] - (mu*yJup[k]) / (rJup**3)*dt
    yJup[k+1] = yJup[k] + vyJup[k+1]*dt
 
 
 
#-----SATURN-----#
 
#Create an array, for all variables, of size N with all entries equal to zero:
xSat = np.zeros((N,))
ySat = np.zeros((N,))
vxSat = np.zeros((N,))
vySat = np.zeros((N,))
 
# Initial Conditions:
xSat[0] = rSat                   # (x0 = r, y0 = 0) in AU
vySat[0] = np.sqrt(mu/rSat)      # (vx0 = 0, vy0 = sqrt(mu/r)) AU/yr
 
#Implement Verlet Algorithm:
for k in range(0,N-1):
    vxSat[k+1] = vxSat[k] - (mu*xSat[k]) / (rSat**3)*dt
    xSat[k+1] = xSat[k] + vxSat[k+1]*dt
    vySat[k+1] = vySat[k] - (mu*ySat[k]) / (rSat**3)*dt
    ySat[k+1] = ySat[k] + vySat[k+1]*dt
 
 
#-----URANUS-----#
 
#Create an array, for all variables, of size N with all entries equal to zero:
xUra = np.zeros((N,))
yUra = np.zeros((N,))
vxUra = np.zeros((N,))
vyUra = np.zeros((N,))
 
# Initial Conditions:
xUra[0] = rUra                   # (x0 = r, y0 = 0) in AU
vyUra[0] = np.sqrt(mu/rUra)      # (vx0 = 0, vy0 = sqrt(mu/r)) AU/yr
 
#Implement Verlet Algorithm:
for k in range(0,N-1):
    vxUra[k+1] = vxUra[k] - (mu*xUra[k]) / (rUra**3)*dt
    xUra[k+1] = xUra[k] + vxUra[k+1]*dt
    vyUra[k+1] = vyUra[k] - (mu*yUra[k]) / (rUra**3)*dt
    yUra[k+1] = yUra[k] + vyUra[k+1]*dt
 
 
#-----NEPTUNE-----#
 
#Create an array, for all variables, of size N with all entries equal to zero:
xNep = np.zeros((N,))
yNep = np.zeros((N,))
vxNep = np.zeros((N,))
vyNep = np.zeros((N,))
 
# Initial Conditions:
xNep[0] = rNep                   # (x0 = r, y0 = 0) in AU
vyNep[0] = np.sqrt(mu/rNep)      # (vx0 = 0, vy0 = sqrt(mu/r)) AU/yr
 
#Implement Verlet Algorithm:
for k in range(0,N-1):
    vxNep[k+1] = vxNep[k] - (mu*xNep[k]) / (rNep**3)*dt
    xNep[k+1] = xNep[k] + vxNep[k+1]*dt
    vyNep[k+1] = vyNep[k] - (mu*yNep[k]) / (rNep**3)*dt
    yNep[k+1] = yNep[k] + vyNep[k+1]*dt
 
 
#Plot Outter Planets:
plt.plot(xJup, yJup, 'ro', xSat, ySat, 'yo', xUra, yUra, 'bo', xNep, yNep, 'ro')
plt.scatter(0,0, 'r')
plt.title ('Circular Orbits of Outer Planets')
plt.xlabel ('x')
plt.ylabel ('y')
plt.axis('equal')
plt.show()

            

        
      

Aziadocs · (This post was last modified: May-25-2019, 06:39 PM by Aziadocs.)

Hi,
I can see that you defined the variable rEar as constant.That's why you are always having a circle.

        
              $$ F=\frac{Gm_{1}m_{2}}{\left[\left(x_{1}-x_{2}\right)^{2}+\left(y_{1}-y_{2}\right)^{2}\right]^{3/2}}\left(x_{1},y_{1}\right) $$

As you can see, the force has a dependance on the radius an position of the two planets, you can simplify if y2 and x2 (for example sun) stay at 0,0. You probably need to update values of x and y of the planet and input in the Force equation.

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Planetary Motion Simulation

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