Animation of QBO, opens window in Browser

qv.py

from vpython import *

Running = True

def exit_app(evt):
    global Running
    if evt.key == 'q':  # Press 'q' to quit
        print("Exiting simulation...")
        Running = False

scene.bind('keydown', exit_app)
scene.width = 1920
scene.height = 1080
scene.range = 100
earth = sphere(pos=vector(0,0,0), radius=5, color=color.blue)
ring = ring(pos=earth.pos, axis=vector(0,1,0), radius=7, thickness=0.5, color=color.red)
# Arrow position: place it on the edge of the ring
arrow_pos = vector(0, 0, 10)
# Create the directional arrow
arrow_obj = arrow(pos=arrow_pos, axis=vector(0, -1, 0), shaftwidth=0.5, color=color.white)

sun = sphere(radius=2, color=color.yellow, make_trail=True, trail_radius=0.2, retain=30)
moon = sphere(radius=1, color=color.white, make_trail=True, trail_radius=0.1, retain=10)

timer_label = label(pos=vector(0,15,0), text='t = 0.0 yr', height=10, box=False, color=color.white)
annual_label = label(pos=vector(0,20,0), text='declination', height=10, box=False, color=color.white)

obliquity = radians(23.44)
moon_incl = radians(5.145*3)
year = 365.2422
draconic = 27.2122

t = 0
dt = 0.1

# Interval in days
interval = 1.185 * year
# toggle = True

while Running:
    rate(600)
    
    sun.pos = vector(50*cos(2*pi*t/year),
                     50*sin(2*pi*t/year)*sin(obliquity),
                     50*sin(2*pi*t/year)*cos(obliquity))
    
    moon.pos = vector(10*cos(2*pi*t/draconic),
                      10*sin(2*pi*t/draconic)*sin(moon_incl),
                      10*sin(2*pi*t/draconic)*cos(moon_incl))

    
    # Color toggle every 1.185 years
    cycle = int(t // interval)

    if cycle % 2 == 0:
        ring.color = color.green
        arrow_obj.axis =  vector(5, 0, 0)  # CW: tangent points downward

    else:
        ring.color = color.red
        arrow_obj.axis =  vector(-5, 0, 0)  # CW: tangent points upward

    annual_label.color = ring.color

    if abs((t/year) % 1) < dt/year:
        # This block runs only when t is approximately an integer multiple of 'year'
        print(f"Year marker reached: {t/year:.0f}")
        annual_label.text = f'decl = {5*cos(2*pi*t/draconic):.2f}°'
        # annual_label.axis = vector(cos(5*cos(2*pi*t/draconic)*2*pi/180), sin(5*cos(2*pi*t/draconic)*2*pi/180), 0)

    t += dt
    timer_label.text = f'time = {t/year:.2f} yr'

[

Screen.Recording.2025-09-06.232242.mp4

](url)

When lunar declination is positive during an annual synching impulse, the QBO shifts to the GREEN direction, and when the lunar declination is negative, the QBO reverses to the opposite RED direction.