HOW TO PROGRAM A
COMET PARTICLE SYSTEM IN THREE.JS

Step 1: Set up the scene, camera and renderer

Create a THREE.Scene, a PerspectiveCamera and a transparent WebGLRenderer with the pixel ratio capped at 2 (1.5 on phones), then add OrbitControls with slow auto-rotate so the comet drifts behind the page.

Step 2: Add a nebula and starfield

Build one THREE.Points cloud of colour-tinted, twinkling stars on a distant sphere, then scatter soft nebula sprites whose cloud textures are generated once from fractal value noise on a canvas. Use additive glow blending and let each nebula slowly spin.

This is the same sky technique used in the Planet Quest solar system game: thousands of tinted, twinkling stars plus slowly spinning nebula clouds, all in a handful of draw calls so the comet keeps its frame rate.

// Planet Quest style sky: tinted twinkling stars + noise-cloud nebula sprites
const sky = new THREE.Group(); scene.add(sky);
const glow = { blending: THREE.AdditiveBlending, transparent: true, depthWrite: false };

function cloudTex(seed, S = 256) {          // fractal value noise, soft round falloff
  const cv = document.createElement('canvas'); cv.width = cv.height = S;
  const g = cv.getContext('2d'), img = g.createImageData(S, S);
  const hs = (x, y) => { const h = Math.sin(x * 127.1 + y * 311.7 + seed * 74.7) * 43758.5453; return h - Math.floor(h); };
  const vn = (x, y) => { const xi = Math.floor(x), yi = Math.floor(y), xf = x - xi, yf = y - yi,
    u = xf * xf * (3 - 2 * xf), v = yf * yf * (3 - 2 * yf);
    return (hs(xi, yi) * (1 - u) + hs(xi + 1, yi) * u) * (1 - v) + (hs(xi, yi + 1) * (1 - u) + hs(xi + 1, yi + 1) * u) * v; };
  for (let y = 0; y < S; y++) for (let x = 0; x < S; x++) {
    let f = 0, a = 0.5, fr = 4 / S;
    for (let o = 0; o < 5; o++) { f += a * vn(x * fr, y * fr); a *= 0.5; fr *= 2; }
    const dx = x / S - 0.5, dy = y / S - 0.5, fall = Math.max(0, 1 - Math.hypot(dx, dy) * 2);
    const k = (y * S + x) * 4; img.data[k] = img.data[k + 1] = img.data[k + 2] = 255;
    img.data[k + 3] = 255 * Math.min(1, Math.max(0, (f - 0.35) * 1.8)) * fall * fall;
  }
  g.putImageData(img, 0, 0); return new THREE.CanvasTexture(cv);
}

const texs = [cloudTex(1), cloudTex(2), cloudTex(3)];
const cols = [0x7a4cff, 0x2f8fd8, 0xd04c9a, 0x2fc4b0, 0x5a6cff];
for (let i = 0; i < 26; i++) {
  const m = new THREE.SpriteMaterial({ map: texs[i % 3], color: cols[i % cols.length], opacity: 1.6 + Math.random() * 0.8, ...glow });
  m.rotation = Math.random() * Math.PI * 2;
  const s = new THREE.Sprite(m); s.scale.setScalar(260 + Math.random() * 300);
  const az = Math.random() * Math.PI * 2, el = (Math.random() - 0.5) * 1.3;
  s.position.set(Math.cos(az) * Math.cos(el), Math.sin(el), Math.sin(az) * Math.cos(el)).multiplyScalar(450);
  s.userData.spin = (Math.random() - 0.5) * 0.02; sky.add(s);
}
// in animate(): sky.children.forEach(s => { if (s.isSprite) s.material.rotation += s.userData.spin * dt; });

Step 3: Shape the rocky nucleus

Displace the vertices of a low-detail IcosahedronGeometry with 3D value noise and craters, then light it inside a ShaderMaterial with a fixed sun direction and a Fresnel rim, so no scene lights are needed.

Step 4: Emit the dust tail, ion tail and debris

Store position, velocity and life for every particle in typed arrays on one BufferGeometry. Dust drifts away from the sun and curves sideways, the blue ion tail streams straight away from the sun, and debris sparkles as it tumbles off.

Step 5: Add the glowing coma

Draw three large soft point sprites at the nucleus with additive blending to fake a bloom-like coma that pulses gently.

Step 6: Animate the particles every frame

In the render loop, step each particle, respawn it at the nucleus when its life runs out, upload the changed buffers, rotate the nucleus and update the shader time uniforms.