Gaze upon it and weep

import random
import math
import pygame
G = 6.67384 * pow(10,-11)
random.seed()
'''Variables that need to be kept around long-term begin with upper case letters
Variables which are used quickly begin with lower case letters'''

def StarCluster(ObjectCount):
    global G
    StarMassLow = 0.2 * pow(10, 30)
    StarMassHigh = 2 * pow(10, 30)
    ZoomLevel = 4.73 * pow(10, 15)
    '''0.5 LY per pixel'''
    Timestep = 10000 * 3.16 * pow(10, 7)
    '''10000 Year per timestep'''
    Spacing = 16 * 9.46 * pow(10, 15)
    '''Number of square LY per star'''
    GenDisplacement = int(pow(ObjectCount * pow(Spacing,2), 0.5))
    '''Calculate max magnitude of X and Y'''
    MinDistance = 4.73 * pow(10, 15)
    '''Being closer than this distance won't increase acceleration of object'''
    ObjectMass = []
    ObjectX = []
    ObjectY = []
    ObjectVX = []
    ObjectVY = []
    for iteration in range (0, ObjectCount):
        ObjectMass.append(random.randint(StarMassLow, StarMassHigh))
        ObjectX.append(random.randint(0, GenDisplacement))
        ObjectY.append(random.randint(0, GenDisplacement))
        ObjectVX.append(0)
        ObjectVY.append(0)
        print('Created Object %s.' % (iteration + 1))
    screen = pygame.display.set_mode((800,800))
    while True:
        for a in range (0, ObjectCount):
            '''a is the object that will have acceleration changed'''
            for b in range (0, ObjectCount):
                '''b is the object that will change it'''
                if a != b:
                    distance = pow(pow(ObjectX[a]-ObjectX[b],2)+pow(ObjectY[a]-ObjectY[b],2), 0.5)
                    if distance < MinDistance:
                        distance = MinDistance
                    dv = - ((G * ObjectMass[b]) / pow(distance, 2)) * Timestep
                    if ObjectX[b] - ObjectX[a] >= 0:
                        angle = math.atan((ObjectY[b] - ObjectY[a])/(ObjectX[b] - ObjectX[a]))
                    if ObjectX[b] - ObjectX[a] < 0:
                        angle = math.atan((ObjectY[b] - ObjectY[a])/(ObjectX[b] - ObjectX[a])) + math.pi
                    ObjectVX[a] += dv * math.cos(angle)
                    ObjectVY[a] += dv * math.sin(angle)
                    '''if a == 0 and b == 1:
                        print('Calculation object %s with object %s done, dv was %s and angle was %s' % (a+1, b+1, round(dv,8), round(math.degrees(angle),0))) #debugging line'''
        for a in range (0, ObjectCount):
            ObjectX[a] += ObjectVX[a]
            ObjectY[a] += ObjectVY[a]
            '''if a == 0:
                print('Object %s at position %s , %s with velocity %s , %s' % (a+1, round(ObjectX[a],1), round(ObjectY[a],1), round(ObjectVX[a],2), round(ObjectVY[a],2))) #debugging line'''
        for a in range (0, ObjectCount):
            screen.set_at((int(ObjectX[a] / ZoomLevel), int(ObjectY[a] / ZoomLevel)), (255,255,255))
            pygame.event.get()
            print("Object %s at %s , %s" % (a+1, int(ObjectX[a] / ZoomLevel), int(ObjectY[a] / ZoomLevel)))
print('Welcome to gravity simulator')
print('Please select which mode you wish to use')
print('1: Star Cluster Mode')
print('2: Our Solar System Mode')
print('3: Accretion Disk Mode')
mode = int(input('Select Mode:'))
if mode == 1:
    print('Star Cluster Mode selected')
    ObjectCount = int(input('Select number of stars:'))
    StarCluster(ObjectCount)