Why Planets Wander (in Coffescript via js2coffee.org) original source: Khan Academy: https://www.khanacademy.org/cs/spin-off-of-why-planets-wander/2207805122

planets-wander.coffee

#
# * Simulation of telescope on Earth looking at the night
# * sky (ignoring the rotation of the Earth).
# * 
# * Telescope angles relative to vernal equinox (First Point of Aries).
# * 
# *   - Planets -
# * Green: Mercury
# * Gray: Venus
# * Brown: Mars
# * 
# *   - Controls -
# * Spacebar: run/pause
# * r: reset telescope
# * Click: fix the telescope to a certain angle
# * Arrow keys to move telescopes
# * 
# * The planet sizes are correct relative to one another,
# * but not relative to the orbit size.
# * The sun's size is not to scale.
#
telescopeAngle = 160
speed = 1 # Change in days per update
resolution = 20 # How accurate orbit speed is

# Position and size or sun
sunX = 225
sunY = 165
sunR = 25
marsData =
  name: "Mars"
  size: 8
  colour: color(212, 95, 17)
  perihelion: 207 # million km
  aperihelion: 249 # million km
  peri_longitude: 336 # degrees
  asc_longitude: 49.6 # degrees
  inclination: 1.85 # degrees
  year: 686.98 # earth days
  mass: 0.64 # 10^24 kg

earthData =
  name: "Earth"
  size: 15
  colour: color(61, 100, 255)
  perihelion: 147 # million km
  aperihelion: 152 # million km
  peri_longitude: 102 # degrees
  asc_longitude: 348.7 # degrees
  inclination: 0 # degrees (by defintion)
  year: 365.25 # earth days
  mass: 5.97 # 10^24 kg

venusData =
  name: "Venus"
  size: 14
  colour: color(149, 175, 196)
  perihelion: 107 # million km
  aperihelion: 109 # million km
  peri_longitude: 131.5 # degrees
  asc_longitude: 76.7 # degrees
  inclination: 3.39 # degrees
  year: 224.7 # earth days
  mass: 4.87 # 10^24 kg

mercuryData =
  name: "Mercury"
  size: 6
  colour: color(82, 171, 88)
  perihelion: 46 # million km
  aperihelion: 69.8 # million km
  peri_longitude: 77 # degrees
  asc_longitude: 48.3 # degrees
  inclination: 7.00 # degrees
  year: 87.97 # earth days
  mass: 0.33 # 10^24 kg


# At 6pm 28th August 2003, Earth and Mars in opposition
_year = 2003
_day = 239.75

# Angles from ellipse centres, not sun (angle from sun = 335.0)
earthAngle = 335.6
marsAngle = 335.1
venusAngle = 170 #approximately
mercuryAngle = 320 #approximately

# Scale down image to fit on screen
scalingFactor = 0.65
running = true
divider = 320
dividerDrag = false
Sun = ->
  @x = sunX
  @y = sunY
  @r = sunR
  @name = "Sun"
  @mass = 330000
  @inclination = 0
  @update = (t) ->

  @draw = ->
    noStroke()
    fill 255, 255, 0
    ellipse @x, @y, sunR, sunR
    fill 255, 89, 0, 100
    ellipse @x, @y, sunR + 3, sunR + 3

  @display = (x, y, r) ->
    x = x or @x
    y = y or @y
    r = r or sunR
    noStroke()
    fill 255, 255, 0
    ellipse x, y, r, r
    fill 255, 89, 0, 100
    ellipse x, y, r + 3, r + 3

  @drawCenter = ->
    fill 255, 255, 255
    ellipse @x, @y, 2, 2

Planet = (data, angle) ->
  @name = data.name
  @year = data.year
  @r = data.size
  
  # Distance from ellipse centre to sun
  focusDist = scalingFactor * (data.aperihelion - data.perihelion) / 2
  
  # Ellipse axes
  major = scalingFactor * data.aperihelion - focusDist
  minor = sqrt(major * major - focusDist * focusDist)
  
  # Store these to save repeatedly calculating them
  phi = data.peri_longitude
  cosPhi = cos(phi)
  sinPhi = sin(phi)
  
  # Angle relative the perihelion
  @angle = angle - phi
  
  # Center of ellipse
  cx = sunX - focusDist * cosPhi
  cy = sunY + focusDist * sinPhi
  
  # Handy properties for calculations
  eccentricity = focusDist / major
  angleConstant = 360 * major * minor / data.year
  
  # Add a numbers of days to the orbit
  @update = (days) ->
    sign = (if days < 0 then -1 / resolution else 1 / resolution)
    speed = 0
    d = 0

    while d < abs(days) * resolution
      
      # Distance from sun
      r = major * (1 - eccentricity * eccentricity) / (1 + eccentricity * cos(@angle))
      
      # Update angle around sun
      @angle += sign * angleConstant / (r * r)
      speed += angleConstant / (r * r)
      d++
    r = major * (1 - eccentricity * eccentricity) / (1 + eccentricity * cos(@angle))
    
    # Position based on non-rotated ellipse
    x = r * cos(@angle) + focusDist
    y = r * sin(@angle)
    
    # Rotate based on ellipse rotation
    @x = cx + x * cosPhi - y * sinPhi
    @y = cy - x * sinPhi - y * cosPhi
    
    # Calculating position above/below plane of Earth's orbit
    # Must be a better method
    angle = atan2(@y - sunY, @x - sunX)
    angle = (360 - angle) % 360
    dAngle = (angle - data.asc_longitude + 540) % 360 - 180
    
    #dAngle /= 90;
    #if (dAngle > 1) { dAngle = 2 - dAngle; }
    #if (dAngle < -1) { dAngle = -2 - dAngle; }
    @inclination = data.inclination * sin(dAngle)

  @update 0
  @display = (x, y, r) ->
    x = x or @x
    y = y or @y
    r = r or data.size
    noStroke()
    fill data.colour
    ellipse x, y, r, r

  @drawCycle = ->
    translate cx, cy
    rotate phi
    ellipse 0, 0, major * 2, minor * 2
    resetMatrix()

  @drawCenter = ->
    stroke 255, 255, 255, 100
    dx = major * cosPhi
    dy = major * sinPhi
    line cx + dx, cy - dy, cx - dx, cy + dy
    fill data.colour
    ellipse cx, cy, 2, 2

  @draw = ->
    fill data.colour
    for i of @previous_points
      p = @previous_points[i]
      ellipse p[0], p[1], 2, 2
    @display @x, @y


###
Make planets here
###
sun = new Sun()
mars = new Planet(marsData, marsAngle)
earth = new Planet(earthData, earthAngle)
venus = new Planet(venusData, venusAngle)
mercury = new Planet(mercuryData, mercuryAngle)
bodies = [sun, mercury, venus, earth, mars]
createRandomStars = (n) ->
  stars = []
  i = 0

  while i < n
    x = random() * 360
    y = random() * 400
    c = random() * 200 + 50
    stars.push [x, y, c]
    i++
  stars


#var stars = createRandomStars(320);
stars = [[2.10, 29.09, 191], [2.29, 59.15, 166], [2.35, -45.75, 54], [3.31, 15.18, 113], [4.86, -8.82, 68], [6.41, -77.26, 115], [6.55, -43.68, 52], [6.57, -42.31, 152], [9.24, 53.90, 62], [9.83, 30.86, 83], [10.13, 56.54, 169], [10.90, -17.99, 195], [12.27, 57.82, 73], [14.18, 60.72, 180], [14.19, 38.50, 55], [16.52, -46.72, 80], [17.10, -55.25, 52], [17.15, -10.18, 73], [17.43, 35.62, 193], [21.01, -8.18, 66], [21.45, 60.24, 127], [22.09, -43.32, 75], [22.81, -49.07, 52], [22.87, 15.35, 65], [24.43, -57.24, 586], [24.50, 48.63, 66], [26.02, -15.94, 71], [27.87, -10.33, 60], [28.27, 29.58, 75], [28.38, 19.29, 54], [28.60, 63.67, 78], [28.66, 20.81, 128], [28.99, -51.61, 62], [29.69, -61.57, 110], [30.00, -21.08, 50], [30.51, 2.76, 57], [30.86, 72.42, 52], [30.97, 42.33, 187], [31.79, 23.46, 200], [32.39, 34.99, 100], [34.13, -51.51, 68], [37.95, 89.26, 204], [40.83, 3.24, 68], [42.50, 27.26, 66], [42.67, 55.90, 59], [43.56, 52.76, 52], [44.11, -8.90, 54], [44.57, -40.30, 109], [45.57, 4.09, 138], [46.20, 53.51, 106], [46.29, 38.84, 80], [47.04, 40.96, 188], [47.37, 44.86, 58], [48.02, -28.99, 52], [49.88, -21.76, 62], [51.08, 49.86, 231], [51.20, 9.03, 66], [51.79, 9.73, 60], [53.24, -9.46, 60], [55.73, 47.79, 99], [55.81, -9.77, 69], [56.05, -64.81, 55], [56.08, 32.29, 56], [56.22, 24.11, 61], [56.30, 42.58, 59], [56.46, 24.37, 55], [56.81, -74.24, 84], [56.87, 24.11, 111], [57.29, 24.05, 65], [58.53, 31.88, 112], [59.46, 40.01, 107], [59.51, -13.51, 102], [59.74, 35.79, 51], [60.17, 12.49, 75], [60.79, 5.99, 53], [62.17, 47.71, 51], [63.50, -42.29, 55], [63.61, -62.47, 80], [64.47, -33.80, 68], [64.95, 15.63, 64], [65.73, 17.54, 59], [66.01, -34.02, 51], [67.14, 15.96, 56], [67.15, 19.18, 69], [67.17, 15.87, 76], [68.50, -55.05, 81], [68.89, -30.56, 57], [68.98, 16.51, 444], [69.08, -3.35, 52], [69.55, -14.30, 53], [72.46, 6.96, 88], [72.80, 5.61, 62], [73.56, 2.44, 61], [74.25, 33.17, 124], [75.49, 43.82, 98], [75.62, 41.08, 62], [76.37, -22.37, 88], [76.63, 41.23, 88], [76.96, -5.09, 116], [78.23, -16.21, 82], [78.63, -8.20, 706], [79.17, 46.00, 489], [79.40, -6.84, 66], [81.12, -2.40, 78], [81.28, 6.35, 257], [81.57, 28.61, 255], [82.06, -20.76, 114], [82.80, -35.47, 55], [83.00, -0.30, 168], [83.18, -17.82, 134], [83.41, -62.49, 59], [83.78, 9.93, 76], [83.86, -5.91, 119], [84.05, -1.20, 248], [84.41, 21.14, 102], [84.69, -2.60, 59], [84.91, -34.07, 127], [85.19, -1.94, 239], [86.12, -22.45, 67], [86.74, -14.82, 68], [86.82, -51.07, 55], [86.94, -9.67, 191], [87.74, -35.77, 92], [87.83, -20.88, 59], [87.87, 39.15, 51], [88.79, 7.41, 586], [89.10, -14.17, 61], [89.79, -42.82, 51], [89.88, 54.28, 61], [89.88, 44.95, 214], [89.93, 37.21, 127], [93.71, -6.27, 50], [93.72, 22.51, 81], [95.08, -30.06, 99], [95.53, -33.44, 55], [95.67, -17.96, 203], [95.74, 22.51, 109], [95.99, -52.70, 1230], [97.20, -7.03, 59], [99.17, -19.26, 51], [99.43, 16.40, 210], [99.44, -43.20, 89], [100.98, 25.13, 96], [101.29, -16.71, 2156], [101.32, 12.90, 78], [102.05, -61.94, 83], [102.46, -32.51, 71], [102.48, -50.61, 104], [103.20, 33.96, 66], [103.53, -24.18, 54], [104.66, -28.97, 283], [105.43, -27.93, 71], [105.76, -23.83, 99], [107.10, -26.39, 225], [107.19, -70.50, 58], [109.21, -67.96, 51], [109.29, -37.10, 122], [109.52, 16.54, 67], [110.03, 21.98, 69], [111.02, -29.30, 146], [111.43, 27.80, 58], [111.79, 8.29, 108], [112.31, -43.30, 84], [113.65, 31.89, 208], [114.71, -26.80, 57], [114.83, 5.23, 615], [115.31, -9.55, 52], [115.45, -72.61, 52], [115.95, -28.95, 52], [116.11, 24.40, 67], [116.31, -37.97, 65], [116.33, 28.03, 363], [117.32, -24.86, 79], [118.05, -40.58, 61], [119.19, -52.98, 73], [120.90, -40.00, 173], [121.89, -24.30, 113], [122.38, -47.34, 238], [124.13, 9.19, 69], [125.63, -59.51, 220], [126.42, -3.91, 53], [126.43, -66.14, 59], [127.57, 60.72, 78], [130.03, -35.31, 51], [130.07, -52.92, 66], [130.16, -46.65, 59], [130.90, -33.19, 62], [131.17, 18.15, 52], [131.18, -54.71, 197], [131.51, -46.04, 55], [131.69, 6.42, 77], [133.76, -60.64, 56], [133.85, 5.95, 93], [134.80, 48.04, 91], [135.91, 47.16, 67], [136.04, -47.10, 59], [137.00, -43.43, 171], [137.74, -58.97, 74], [137.82, -62.32, 51], [138.30, -69.72, 251], [138.59, 2.32, 54], [139.27, -59.28, 173], [139.71, 36.80, 57], [140.26, 34.39, 91], [140.53, -55.01, 144], [141.90, -8.66, 201], [142.81, -57.03, 90], [142.88, 63.06, 63], [143.22, 51.68, 89], [144.96, -1.14, 54], [145.29, 9.89, 70], [146.31, -62.51, 62], [146.46, 23.77, 102], [146.78, -65.07, 106], [147.75, 59.04, 58], [148.19, 26.01, 54], [149.22, -54.57, 70], [151.83, 16.76, 72], [152.09, 11.97, 312], [152.65, -12.35, 66], [153.43, -70.04, 82], [153.68, -42.12, 55], [154.17, 23.42, 74], [154.27, -61.33, 76], [154.27, 42.91, 73], [154.99, 19.84, 199], [155.58, 41.50, 96], [156.52, -16.84, 56], [156.97, -58.74, 57], [158.01, -61.69, 81], [158.20, 9.31, 56], [159.33, -48.23, 56], [160.74, -64.39, 120], [161.69, -49.42, 124], [162.41, -16.19, 93], [163.33, 34.22, 58], [163.37, -58.85, 58], [165.46, 56.38, 155], [165.93, 61.75, 228], [167.15, -58.98, 52], [167.42, 44.50, 100], [168.53, 20.52, 136], [168.56, 15.43, 80], [169.62, 33.09, 71], [169.84, -14.78, 68], [170.25, -54.49, 54], [172.85, 69.33, 57], [173.25, -31.86, 69], [173.95, -63.02, 93], [176.40, -66.73, 65], [176.51, 47.78, 62], [177.27, 14.57, 182], [177.67, 1.77, 66], [178.46, 53.69, 151], [182.09, -50.72, 134], [182.53, -22.62, 99], [182.91, -52.37, 51], [183.79, -58.75, 116], [183.86, 57.03, 81], [183.95, -17.54, 134], [184.98, -0.67, 54], [185.34, -60.40, 66], [186.65, -63.10, 469], [187.01, -50.23, 53], [187.47, -16.52, 104], [187.79, -57.11, 266], [188.12, -72.13, 56], [188.37, 69.79, 55], [188.60, -23.40, 127], [189.30, -69.14, 124], [189.43, -48.54, 55], [190.38, -48.96, 174], [190.42, -1.45, 73], [191.57, -68.11, 97], [191.93, -59.69, 336], [193.51, 55.96, 236], [193.90, 3.40, 76], [194.01, 38.32, 108], [195.54, 10.96, 111], [195.57, -71.55, 66], [199.73, -23.17, 101], [200.15, -36.71, 119], [200.98, 54.93, 168], [201.30, -11.16, 406], [202.76, -39.41, 54], [203.67, -0.60, 77], [204.97, -53.47, 164], [206.89, 49.31, 222], [207.38, -41.69, 75], [207.40, -42.47, 72], [208.67, 18.40, 125], [208.89, -47.29, 137], [209.57, -42.10, 56], [209.67, -44.80, 55], [210.96, -60.37, 524], [211.10, 64.38, 63], [211.59, -26.68, 83], [211.67, -36.37, 192], [213.92, 19.19, 857], [214.85, -46.06, 68], [217.96, 30.37, 67], [218.02, 38.31, 97], [218.88, -42.16, 159], [219.91, -60.84, 316], [219.92, -60.84, 794], [220.29, 13.73, 58], [220.48, -47.39, 162], [220.63, -64.97, 88], [220.76, -5.66, 54], [221.25, 27.07, 157], [221.56, 1.89, 60], [221.97, -79.04, 56], [222.68, 74.16, 191], [222.72, -16.04, 119], [224.63, -43.13, 125], [224.79, -42.10, 91], [225.49, 40.39, 71], [226.02, -25.28, 84], [226.28, -47.05, 53], [227.98, -48.74, 54], [228.07, -52.10, 75], [228.88, 33.32, 73], [229.25, -9.38, 131], [229.73, -68.68, 109], [230.18, 71.83, 100], [230.34, -40.65, 86], [230.45, -36.26, 67], [230.67, -44.69, 77], [231.23, 58.97, 82], [231.96, 29.11, 63], [233.67, 26.71, 172], [233.70, 10.54, 57], [233.79, -41.17, 115], [233.88, -14.79, 54], [234.26, -28.14, 66], [234.66, -29.78, 63], [235.69, 26.30, 57], [236.07, 6.43, 128], [236.55, 15.42, 64], [237.41, -3.43, 69], [237.70, 4.48, 61], [237.74, -33.63, 51], [238.79, -63.43, 112], [239.11, 15.66, 55], [239.22, -29.21, 55], [239.71, -26.11, 108], [240.03, -38.40, 75], [240.08, -22.62, 164], [241.36, -19.81, 136], [241.70, -20.67, 52], [243.59, -3.69, 121], [243.86, -63.69, 55], [244.58, -4.69, 85], [244.94, 46.31, 53], [245.30, -25.59, 107], [245.48, 19.15, 60], [246.00, 61.51, 120], [247.35, -26.43, 384], [247.56, 21.49, 116], [247.73, 1.98, 57], [248.36, -78.90, 54], [248.97, -28.22, 113], [249.29, -10.57, 138], [250.32, 31.60, 106], [250.72, 38.92, 72], [252.17, -69.03, 213], [252.45, -59.04, 59], [252.54, -34.29, 164], [252.97, -38.05, 100], [253.08, -38.02, 68], [253.65, -42.36, 65], [254.42, 9.38, 88], [254.66, -55.99, 92], [255.07, 30.93, 53], [257.20, 65.71, 89], [257.59, -15.73, 99], [258.04, -43.24, 80], [258.66, 14.39, 116], [258.76, 24.84, 91], [258.76, 36.81, 90], [260.50, -25.00, 83], [261.32, -55.53, 112], [261.35, -56.38, 81], [262.61, 52.30, 116], [262.69, -37.30, 123], [262.77, -60.68, 66], [262.96, -49.88, 112], [263.40, -37.10, 260], [263.73, 12.56, 189], [264.33, -43.00, 220], [264.40, -15.40, 69], [264.87, 46.01, 57], [265.62, -39.03, 153], [265.87, 4.57, 118], [266.43, -64.72, 66], [266.62, 27.72, 75], [266.90, -40.13, 101], [266.97, 2.71, 59], [267.46, -37.04, 88], [268.38, 56.87, 60], [269.06, 37.25, 55], [269.15, 51.49, 169], [269.44, 29.25, 62], [269.76, -9.77, 80], [270.16, 2.93, 52], [271.45, -30.42, 101], [271.66, -50.09, 64], [271.84, 9.56, 60], [271.89, 28.76, 56], [273.44, -21.06, 56], [274.41, -36.76, 93], [275.25, -29.83, 121], [275.26, 72.73, 67], [275.33, -2.90, 84], [275.92, 21.77, 55], [276.04, -34.38, 231], [276.74, -45.97, 71], [276.99, -25.42, 113], [278.80, -8.24, 55], [279.23, 38.78, 784], [281.41, -26.99, 89], [282.52, 33.36, 70], [283.82, -26.30, 193], [284.43, -21.11, 70], [284.74, 32.69, 84], [285.65, -29.88, 132], [286.17, -21.74, 59], [286.35, 13.86, 101], [286.56, -4.88, 74], [286.74, -27.67, 80], [287.44, -21.02, 109], [288.14, 67.66, 95], [289.28, 53.37, 57], [290.42, -17.85, 52], [290.66, -44.46, 51], [290.97, -40.62, 51], [291.37, 3.11, 78], [292.43, 51.73, 59], [292.68, 27.96, 97], [296.24, 45.13, 110], [296.56, 10.61, 121], [296.85, 18.53, 62], [297.04, 70.27, 56], [297.69, 8.87, 469], [298.12, 1.01, 55], [298.83, 6.41, 61], [299.08, 35.08, 54], [299.69, 19.49, 70], [300.15, -72.91, 51], [302.17, -66.18, 68], [302.83, -0.82, 85], [303.41, 46.74, 57], [303.87, 47.71, 51], [304.51, -12.54, 67], [305.25, -14.78, 97], [305.56, 40.26, 171], [306.41, -56.73, 208], [309.39, 14.60, 64], [309.39, -47.29, 93], [309.91, 15.91, 59], [310.36, 45.28, 336], [311.24, -66.20, 75], [311.32, 61.84, 74], [311.55, 33.97, 146], [311.92, -9.50, 58], [313.70, -58.45, 63], [314.29, 41.17, 52], [316.23, 43.93, 61], [318.23, 30.23, 86], [318.70, 38.04, 57], [318.96, 5.25, 53], [319.64, 62.59, 147], [321.67, -22.41, 59], [322.16, 70.56, 85], [322.89, -5.57, 107], [323.50, 45.59, 51], [325.02, -16.66, 62], [325.37, -77.39, 59], [326.05, 9.88, 154], [326.76, -16.13, 109], [328.48, -37.36, 100], [331.45, -0.32, 104], [331.75, 25.35, 59], [332.06, -46.96, 239], [332.55, 6.20, 69], [332.71, 58.20, 76], [334.63, -60.26, 109], [335.41, -1.39, 56], [337.21, -0.02, 64], [337.32, -43.50, 51], [337.82, 50.28, 59], [340.37, 10.83, 75], [340.67, -46.88, 191], [340.75, 30.22, 105], [341.63, 23.57, 51], [342.14, -51.32, 72], [342.42, 66.20, 71], [342.50, 24.60, 72], [343.15, -7.58, 60], [343.66, -15.82, 83], [344.41, -29.62, 358], [345.48, 42.33, 65], [345.94, 28.08, 147], [346.19, 15.21, 142], [347.36, -21.17, 62], [347.59, -45.25, 54], [349.29, 3.28, 62], [349.36, -58.24, 50], [350.74, -20.10, 51], [354.39, 46.46, 57], [354.84, 77.63, 86], [79.17, 46.01, 411], [113.65, 31.89, 111], [190.42, -1.45, 70], [200.98, 54.92, 52], [257.59, -15.73, 76]]

###
Telescope
###
Telescope = (base, angle) ->
  @fixedAngle = false
  t = 400
  @x = base.x
  @y = base.y
  @angle = base.angle + angle
  @draw = ->
    
    #
    #        var x1 = this.x + t * cos(this.angle + this.max_a) / 2;
    #        var y1 = this.y + t * sin(this.angle + this.max_a) / 2;
    #        var x2 = this.x + t * cos(this.angle - this.max_a) / 2;
    #        var y2 = this.y + t * sin(this.angle - this.max_a) / 2;
    #        triangle(this.x, this.y, x1, y1, x2, y2);
    #        
    start = @angle - telescopeAngle / 2
    end = start + telescopeAngle
    fill 255, 255, 255, 3
    i = 0

    while i < t
      arc @x, @y, i, i, start, end
      i += 8

  @update = ->
    theta = undefined
    if @fixedAngle is false
      theta = atan2(base.y - sunY, base.x - sunX)
    else
      theta = @fixedAngle
    @x = base.x + base.r * cos(theta) / 2
    @y = base.y + base.r * sin(theta) / 2
    @angle = theta

telescope = new Telescope(earth, 0)

###
Display functions
###
sortByDist = (a, b) ->
  distA = dist(a.x, a.y, telescope.x, telescope.y)
  distB = dist(b.x, b.y, telescope.x, telescope.y)
  distB - distA

drawTelescopeAngles = ->
  fill 240
  textSize 11
  textAlign CENTER, BASELINE
  angle = undefined
  if telescope.fixedAngle isnt false
    angle = round(telescope.fixedAngle)
  else
    angle = round(telescope.angle) % 360
  i = 0

  while i < 360
    a = i - angle
    a += 360  if a < -180
    a -= 360  if a > 180
    x = 200 + a * 400 / telescopeAngle
    text i + "°", x, 398
    i += 20

drawView = ->
  fill 0
  stroke 255
  h = 400 - divider
  rect -1, divider - 1, 401, h + 1
  
  # Stars
  i = 0

  while i < stars.length
    s = stars[i]
    x = (360 + s[0] - telescope.angle) % 360
    x = x - 360  if x > 180
    if x < telescopeAngle
      stroke s[2]
      px = round(200 + x * 400 / telescopeAngle)
      py = 400 - h / 2 + s[1] * h / 180
      point px, py
    i++
  noStroke()
  tx = telescope.x
  ty = telescope.y
  
  # Sort non-Earth bodies by distance from Earth
  others = [sun, mercury, venus, mars].sort(sortByDist)
  for i of others
    body = others[i]
    theta = atan2(ty - body.y, tx - body.x)
    dTheta = (180 + telescope.angle - theta) % 360
    dTheta -= 360  if dTheta > 180
    d = dist(body.x, body.y, tx, ty)
    r = 100 * atan(body.r / d) / 180
    if abs(dTheta) <= telescopeAngle / 2 + r
      x = 200 - 400 * dTheta / telescopeAngle
      y = 400 - h / 2 + body.inclination * h / telescopeAngle
      body.display x, y, r
  
  # Draw arrows
  stroke 200
  fill 255, 255, 255, 80
  triangle 192, divider - 3, 208, divider - 3, 200, divider - 14
  triangle 192, divider + 3, 208, divider + 3, 200, divider + 14
  if mouseX > 190 and mouseX < 210 and mouseY > divider - 15 and mouseY < divider + 15
    fill 255, 255, 255, 200
    if mouseY < divider
      triangle 192, divider - 3, 208, divider - 3, 200, divider - 14
    else
      triangle 192, divider + 3, 208, divider + 3, 200, divider + 14
  drawTelescopeAngles()


# Menu
menu_x = 5
menu_y = 5
menu_w = 93
menu_h = bodies.length * 26 + 26
drawKey = ->
  x = menu_x
  y = menu_y
  
  # Outline
  stroke 120, 120, 120, 120
  fill 0, 0, 0, 200
  rect x, y, menu_w, menu_h
  
  # Title
  textSize 16
  textAlign CENTER, BASELINE
  fill 240
  text "Key", x + menu_w / 2, y + 18
  textSize 13
  textAlign LEFT, CENTER
  i = 0

  while i < bodies.length
    bodies[i].display x + 19, y + i * 26 + 40
    fill 255
    text bodies[i].name, x + 37, y + i * 26 + 40
    i++

draw = ->
  if running
    j = 0

    while j < speed
      i = 1

      while i < bodies.length
        bodies[i].update 1
        i++
      j++
    telescope.update()
  background 0, 0, 0
  noStroke()
  telescope.draw()
  for i of bodies
    bodies[i].draw()
  drawView()
  drawKey()
  fill 255
  textSize 12
  textAlign LEFT, BASELINE
  a = round((360 + telescope.angle) % 360)
  text "Telescope aimed at " + a + "°", 3, divider - 4
  textAlign RIGHT, BASELINE
  if telescope.fixedAngle is false
    text "Click anywhere to aim telescope", 397, divider - 4
  else
    text "Reset telescope", 397, divider - 4


###
Event handling
###
mousePressed = ->
  dividerDrag = true  if mouseX > 190 and mouseX < 210 and mouseY > divider - 15 and mouseY < divider + 15

mouseDragged = ->
  divider = constrain(mouseY, menu_h + 24, 360)  if dividerDrag

mouseReleased = ->
  if telescope.fixedAngle isnt false and mouseX > 300 and mouseY > divider - 15 and mouseY < divider
    telescope.fixedAngle = false
  else unless dividerDrag
    angle = atan2(mouseY - telescope.y, mouseX - telescope.x)
    angle = (360 + angle) % 360
    telescope.fixedAngle = angle
  dividerDrag = false

mouseOut = ->
  dividerDrag = false

keyPressed = ->
  
  # Spacebar toggles animation
  running = not running  if keyCode is 32
  telescope.fixedAngle = false  if keyCode is 82
  if keyCode is LEFT and telescope.fixedAngle isnt false
    telescope.fixedAngle -= 2
    telescope.fixedAngle += 360  if telescope.fixedAngle < 0
  telescope.fixedAngle = (telescope.fixedAngle + 2) % 360  if keyCode is RIGHT and telescope.fixedAngle isnt false