orbit.py

### Graphics Variables
from Tkinter import *

WIDTH = 500.0
HEIGHT = 500.0

root = Tk()
canvas = Canvas(width=WIDTH, height=HEIGHT, bg="black")
moonshape = 0

### Math Variables
from math import *

earth_x = WIDTH / 2
earth_y = HEIGHT / 2
earth_radius = 25.0

orbit_scale_x = 200.0
orbit_scale_y = 100.0
orbit_rotation = -pi / 9.0

moon_radius = 15.0
moon_speed = 10
moon_position = 0.0

def MoonCoords():
    moon_x = (orbit_scale_x * cos(moon_position) * cos(orbit_rotation) 
        - orbit_scale_y * sin(moon_position) * sin(orbit_rotation) + earth_x)
    moon_y = (orbit_scale_x * cos(moon_position) * sin(orbit_rotation) 
        + orbit_scale_y * sin(moon_position) * cos(orbit_rotation) + earth_y)
    return (moon_x, moon_y)

def DrawEarth():
    canvas.create_oval(earth_x - earth_radius,
            earth_y - earth_radius,
            earth_x + earth_radius,
            earth_y + earth_radius,
            width=0,
            fill="blue")

def DrawMoon():
    global moonshape
    moon_x, moon_y = MoonCoords()
    moonshape = canvas.create_oval(moon_x - moon_radius,
            moon_y - moon_radius,
            moon_x + moon_radius,
            moon_y + moon_radius,
            width=0,
            fill="grey")

def UpdateMoon():
    moon_x, moon_y = MoonCoords()
    canvas.coords(moonshape, moon_x - moon_radius,
            moon_y - moon_radius,
            moon_x + moon_radius,
            moon_y + moon_radius)


def Update():
    global moon_position
    moon_position += moon_speed / 1000.0
    UpdateMoon()
    root.after(10, Update)

def Main():
    canvas.pack(expand=YES, fill=BOTH)
    DrawEarth()
    DrawMoon()
    Update()
    root.mainloop()

if __name__ == "__main__":
    Main()