Plenate and moon Design Python programming Demo by G Krishna Chauhan

Source Code

#!/usr/bin/env python3

"""       turtle-example-suite:

        tdemo_planets_and_moon.py

Gravitational system simulation using the

approximation method from Feynman-lectures,

p.9-8, using turtlegraphics.

Example: heavy central body, light planet,

very light moon!

Planet has a circular orbit, moon a stable

orbit around the planet.

You can hold the movement temporarily by

pressing the left mouse button with the

mouse over the scrollbar of the canvas.

"""

from turtle import Shape, Turtle, mainloop, Vec2D as Vec

G = 8

class GravSys(object):

    def __init__(self):

        self.planets = []

        self.t = 0

        self.dt = 0.01

    def init(self):

        for p in self.planets:

            p.init()

    def start(self):

        for i in range(10000):

            self.t += self.dt

            for p in self.planets:

                p.step()

class Star(Turtle):

    def __init__(self, m, x, v, gravSys, shape):

        Turtle.__init__(self, shape=shape)

        self.penup()

        self.m = m

        self.setpos(x)

        self.v = v

        gravSys.planets.append(self)

        self.gravSys = gravSys

        self.resizemode("user")

        self.pendown()

    def init(self):

        dt = self.gravSys.dt

        self.a = self.acc()

        self.v = self.v + 0.5*dt*self.a

    def acc(self):

        a = Vec(0,0)

        for planet in self.gravSys.planets:

            if planet != self:

                v = planet.pos()-self.pos()

                a += (G*planet.m/abs(v)**3)*v

        return a

    def step(self):

        dt = self.gravSys.dt

        self.setpos(self.pos() + dt*self.v)

        if self.gravSys.planets.index(self) != 0:

            self.setheading(self.towards(self.gravSys.planets[0]))

        self.a = self.acc()

        self.v = self.v + dt*self.a

## create compound yellow/blue turtleshape for planets

def main():

    s = Turtle()

    s.reset()

    s.getscreen().tracer(0,0)

    s.ht()

    s.pu()

    s.fd(6)

    s.lt(90)

    s.begin_poly()

    s.circle(6, 180)

    s.end_poly()

    m1 = s.get_poly()

    s.begin_poly()

    s.circle(6,180)

    s.end_poly()

    m2 = s.get_poly()

    planetshape = Shape("compound")

    planetshape.addcomponent(m1,"orange")

    planetshape.addcomponent(m2,"blue")

    s.getscreen().register_shape("planet", planetshape)

    s.getscreen().tracer(1,0)

    ## setup gravitational system

    gs = GravSys()

    sun = Star(1000000, Vec(0,0), Vec(0,-2.5), gs, "circle")

    sun.color("yellow")

    sun.shapesize(1.8)

    sun.pu()

    earth = Star(12500, Vec(210,0), Vec(0,195), gs, "planet")

    earth.pencolor("green")

    earth.shapesize(0.8)

    moon = Star(1, Vec(220,0), Vec(0,295), gs, "planet")

    moon.pencolor("blue")

    moon.shapesize(0.5)

    gs.init()

    gs.start()

    return "Done!"

if __name__ == '__main__':

    main()

    mainloop()