<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <meta name="aspect-ratio" content="1:1">
  <style>
    * {
      box-sizing: border-box;
      margin: 0;
      padding: 0;
    }
    body {
      font-family: system-ui, -apple-system, sans-serif;
      background: #0b132b;
      color: #f8fafc;
      display: flex;
      flex-direction: column;
      align-items: center;
      justify-content: space-between;
      min-height: 100%;
      padding: 12px 8px;
      user-select: none;
    }
    .system-container {
      position: relative;
      width: 100%;
      max-width: 400px;
      aspect-ratio: 1 / 1;
      display: flex;
      align-items: center;
      justify-content: center;
    }
    svg {
      width: 100%;
      height: 100%;
      overflow: visible;
    }
    .orbit-sun {
      transform-origin: 200px 200px;
      animation: spin 14s linear infinite;
    }
    .orbit-earth {
      transform-origin: 200px 70px;
      animation: spin 1.1s linear infinite;
    }
    .counter-spin {
      transform-box: fill-box;
      transform-origin: center;
      animation: counter-spin 14s linear infinite;
    }
    @keyframes spin {
      from { transform: rotate(0deg); }
      to { transform: rotate(-360deg); }
    }
    @keyframes counter-spin {
      from { transform: rotate(0deg); }
      to { transform: rotate(360deg); }
    }
    .paused * {
      animation-play-state: paused !important;
    }
    .controls {
      display: flex;
      gap: 10px;
      align-items: center;
      justify-content: center;
      margin-top: 4px;
      z-index: 10;
    }
    .btn {
      background: #1c2541;
      color: #f8fafc;
      border: 1px solid #3a506b;
      padding: 6px 16px;
      border-radius: 20px;
      font-size: 13px;
      font-weight: 600;
      cursor: pointer;
      display: inline-flex;
      align-items: center;
      gap: 6px;
      outline: none;
    }
    .btn:active {
      background: #3a506b;
    }
    .legend {
      display: flex;
      flex-wrap: wrap;
      justify-content: center;
      gap: 8px 16px;
      font-size: 12px;
      color: #94a3b8;
    }
    .legend-item {
      display: flex;
      align-items: center;
      gap: 6px;
    }
    .dot {
      width: 8px;
      height: 8px;
      border-radius: 50%;
      display: inline-block;
    }
  </style>
</head>
<body>

  <div class="system-container" id="simContainer">
    <svg viewBox="0 0 400 400">
      <defs>
        <radialGradient id="sunGlow" cx="50%" cy="50%" r="50%">
          <stop offset="0%" stop-color="#ffea00" />
          <stop offset="60%" stop-color="#ff9100" />
          <stop offset="100%" stop-color="#ff5400" stop-opacity="0.1" />
        </radialGradient>
        <radialGradient id="earthGrad" cx="35%" cy="35%" r="65%">
          <stop offset="0%" stop-color="#48cae4" />
          <stop offset="60%" stop-color="#0077b6" />
          <stop offset="100%" stop-color="#023e8a" />
        </radialGradient>
      </defs>

      
      <circle cx="200" cy="200" r="130" fill="none" stroke="#3a506b" stroke-width="1.5" stroke-dasharray="5 5" />

      
      <path id="orbitTextPath" d="M 70 200 A 130 130 0 0 1 330 200" fill="none" />
      <text fill="#64748b" font-size="11" font-weight="600" letter-spacing="1">
        <textPath href="#orbitTextPath" startOffset="50%" text-anchor="middle">
          Earth Orbit: 365 Days
        </textPath>
      </text>

      
      <circle cx="200" cy="200" r="42" fill="url(#sunGlow)" opacity="0.3" />
      <circle cx="200" cy="200" r="28" fill="url(#sunGlow)" />
      <text x="200" y="204" fill="#0b132b" font-size="12" font-weight="bold" text-anchor="middle">Sun</text>

      
      <g class="orbit-sun">
        
        <g>
          
          <circle cx="200" cy="70" r="32" fill="none" stroke="#475569" stroke-width="1" stroke-dasharray="3 3" />
          
          
          <g class="orbit-earth">
            <circle cx="200" cy="38" r="4" fill="#e2e8f0" />
          </g>

          
          <circle cx="200" cy="70" r="12" fill="url(#earthGrad)" />
          
          
          <g class="counter-spin">
            <text x="200" y="74" fill="#ffffff" font-size="9" font-weight="bold" text-anchor="middle">Earth</text>
          </g>
        </g>
      </g>
    </svg>
  </div>

  <div class="legend">
    <div class="legend-item">
      <span class="dot" style="background:#0077b6;"></span>
      <span>Earth Orbit: 365 Days</span>
    </div>
    <div class="legend-item">
      <span class="dot" style="background:#cbd5e1;"></span>
      <span>Moon Orbit: ~27 Days</span>
    </div>
  </div>

  <div class="controls">
    <button class="btn" id="playBtn" aria-label="Play or pause animation">
      <span id="btnIcon">⏸</span>
      <span id="btnText">Pause</span>
    </button>
  </div>

  <script>
    const sim = document.getElementById('simContainer');
    const playBtn = document.getElementById('playBtn');
    const btnIcon = document.getElementById('btnIcon');
    const btnText = document.getElementById('btnText');

    let isPlaying = true;

    playBtn.addEventListener('click', () => {
      isPlaying = !isPlaying;
      if (isPlaying) {
        sim.classList.remove('paused');
        btnIcon.textContent = '⏸';
        btnText.textContent = 'Pause';
      } else {
        sim.classList.add('paused');
        btnIcon.textContent = '▶';
        btnText.textContent = 'Play';
      }
    });
  </script>
</body>
</html>

The Earth-Sun-Moon System

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <meta name="aspect-ratio" content="4:3">
  <style>
    * { box-sizing: border-box; margin: 0; padding: 0; font-family: system-ui, -apple-system, sans-serif; }
    body {
      background: #ffffff;
      color: #1e2945;
      padding: 12px;
      display: flex;
      flex-direction: column;
      gap: 12px;
    }
    
    .grid {
      display: grid;
      grid-template-columns: 1fr 1.2fr;
      gap: 12px;
    }

    @media (max-width: 520px) {
      .grid {
        grid-template-columns: 1fr;
      }
    }

    .panel {
      background: #f8fafc;
      border: 1px solid #e2e8f0;
      border-radius: 12px;
      padding: 12px;
      display: flex;
      flex-direction: column;
      position: relative;
    }

    .panel-title {
      font-size: 13px;
      font-weight: 700;
      text-transform: uppercase;
      letter-spacing: 0.5px;
      color: #64748b;
      margin-bottom: 8px;
    }

    /* Size Panel */
    .size-stage {
      display: flex;
      flex-direction: column;
      gap: 8px;
      flex: 1;
      justify-content: space-around;
    }

    .size-row {
      display: flex;
      align-items: center;
      gap: 12px;
      background: #ffffff;
      border: 1px solid #edf2f7;
      border-radius: 8px;
      padding: 8px 12px;
    }

    .size-display {
      width: 64px;
      height: 64px;
      display: flex;
      align-items: center;
      justify-content: center;
      flex-shrink: 0;
    }

    .sun-sphere {
      width: 60px;
      height: 60px;
      border-radius: 50%;
      background: radial-gradient(circle at 35% 35%, #fff176, #f59e0b, #d97706);
      box-shadow: 0 0 16px rgba(245, 158, 11, 0.4);
    }

    .earth-sphere {
      width: 16px;
      height: 16px;
      border-radius: 50%;
      background: radial-gradient(circle at 35% 35%, #60a5fa, #2563eb, #1d4ed8);
      box-shadow: 0 0 6px rgba(37, 99, 235, 0.3);
    }

    .moon-sphere {
      width: 6px;
      height: 6px;
      border-radius: 50%;
      background: radial-gradient(circle at 35% 35%, #f1f5f9, #94a3b8, #64748b);
      box-shadow: 0 0 4px rgba(100, 116, 139, 0.3);
    }

    .obj-info {
      display: flex;
      flex-direction: column;
    }

    .obj-name {
      font-size: 14px;
      font-weight: 700;
      color: #0f172a;
    }

    .obj-sub {
      font-size: 12px;
      color: #64748b;
    }

    /* Distance & Sky Panel */
    .distance-stage {
      display: flex;
      flex-direction: column;
      gap: 12px;
      flex: 1;
      justify-content: space-between;
    }

    .scale-box {
      background: #ffffff;
      border: 1px solid #edf2f7;
      border-radius: 8px;
      padding: 10px;
      display: flex;
      flex-direction: column;
      gap: 8px;
    }

    .distance-track {
      position: relative;
      height: 28px;
      background: #f1f5f9;
      border-radius: 14px;
      display: flex;
      align-items: center;
      padding: 0 10px;
      overflow: hidden;
    }

    .dist-point-earth {
      position: absolute;
      left: 8px;
      width: 14px;
      height: 14px;
      border-radius: 50%;
      background: #2563eb;
      z-index: 2;
    }

    .dist-point-moon {
      position: absolute;
      left: 32px;
      width: 6px;
      height: 6px;
      border-radius: 50%;
      background: #94a3b8;
      z-index: 2;
    }

    .dist-point-sun {
      position: absolute;
      right: 8px;
      width: 22px;
      height: 22px;
      border-radius: 50%;
      background: radial-gradient(circle, #fde047, #f59e0b);
      box-shadow: 0 0 8px #f59e0b;
      z-index: 2;
    }

    .dist-line {
      position: absolute;
      left: 14px;
      right: 18px;
      height: 2px;
      background: #cbd5e1;
      border-top: 2px dashed #94a3b8;
    }

    .distance-labels {
      display: flex;
      justify-content: space-between;
      font-size: 11px;
      font-weight: 600;
      color: #475569;
    }

    /* Sky View Comparison */
    .sky-box {
      background: #0f172a;
      border-radius: 8px;
      padding: 12px;
      color: #ffffff;
      text-align: center;
      display: flex;
      flex-direction: column;
      align-items: center;
      gap: 8px;
    }

    .sky-title {
      font-size: 12px;
      font-weight: 700;
      letter-spacing: 0.5px;
      color: #94a3b8;
      text-transform: uppercase;
    }

    .sky-circles {
      display: flex;
      align-items: center;
      justify-content: center;
      gap: 24px;
      width: 100%;
    }

    .sky-item {
      display: flex;
      flex-direction: column;
      align-items: center;
      gap: 4px;
    }

    .apparent-circle {
      width: 38px;
      height: 38px;
      border-radius: 50%;
      display: flex;
      align-items: center;
      justify-content: center;
      font-size: 18px;
      position: relative;
    }

    .sun-sky {
      background: radial-gradient(circle, #fffbeb, #fde047, #f59e0b);
      box-shadow: 0 0 14px rgba(253, 224, 71, 0.6);
    }

    .moon-sky {
      background: radial-gradient(circle, #ffffff, #cbd5e1, #94a3b8);
      box-shadow: 0 0 10px rgba(255, 255, 255, 0.4);
    }

    .equals-sign {
      font-size: 20px;
      font-weight: bold;
      color: #38bdf8;
    }

    .sky-tag {
      font-size: 11px;
      color: #cbd5e1;
      font-weight: 600;
    }

    .takeaway-pill {
      background: #e0f2fe;
      color: #0369a1;
      font-size: 12px;
      font-weight: 700;
      padding: 4px 10px;
      border-radius: 12px;
      display: inline-flex;
      align-items: center;
      gap: 4px;
    }
  </style>
</head>
<body>

  <div class="grid">
    
    <div class="panel">
      <div class="panel-title">Real Size</div>
      <div class="size-stage">
        
        <div class="size-row">
          <div class="size-display">
            <div class="sun-sphere"></div>
          </div>
          <div class="obj-info">
            <span class="obj-name">Sun</span>
            <span class="obj-sub">Giant Star</span>
          </div>
        </div>

        <div class="size-row">
          <div class="size-display">
            <div class="earth-sphere"></div>
          </div>
          <div class="obj-info">
            <span class="obj-name">Earth</span>
            <span class="obj-sub">Our Planet</span>
          </div>
        </div>

        <div class="size-row">
          <div class="size-display">
            <div class="moon-sphere"></div>
          </div>
          <div class="obj-info">
            <span class="obj-name">Moon</span>
            <span class="obj-sub">Rocky Neighbor</span>
          </div>
        </div>

      </div>
    </div>

    
    <div class="panel">
      <div class="panel-title">Distance & Sky View</div>
      <div class="distance-stage">
        
        <div class="scale-box">
          <div class="distance-track">
            <div class="dist-line"></div>
            <div class="dist-point-earth" title="Earth"></div>
            <div class="dist-point-moon" title="Moon"></div>
            <div class="dist-point-sun" title="Sun"></div>
          </div>
          <div class="distance-labels">
            <span>Moon: 240,000 miles (Close)</span>
            <span>Sun: 93,000,000 miles (Far)</span>
          </div>
        </div>

        <div class="sky-box">
          <div class="sky-title">View From Earth Sky</div>
          <div class="sky-circles">
            <div class="sky-item">
              <div class="apparent-circle sun-sky"></div>
              <span class="sky-tag">Sun</span>
            </div>
            <div class="equals-sign">≈</div>
            <div class="sky-item">
              <div class="apparent-circle moon-sky"></div>
              <span class="sky-tag">Moon</span>
            </div>
          </div>
          <div class="takeaway-pill">
            ✦ Same apparent size!
          </div>
        </div>

      </div>
    </div>
  </div>

</body>
</html>

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Celestial Spheres & Shadows</title>
  <style>
    * {
      box-sizing: border-box;
      margin: 0;
      padding: 0;
      font-family: system-ui, -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif;
    }

    body {
      background: #0b0f19;
      color: #f8fafc;
      display: flex;
      flex-direction: column;
      align-items: center;
      justify-content: center;
      min-height: 100vh;
      max-height: 520px;
      padding: 12px 8px;
      overflow-x: hidden;
    }

    .main-wrapper {
      width: 100%;
      max-width: 600px;
      display: flex;
      flex-direction: column;
      align-items: center;
      gap: 12px;
    }

    .header-bar {
      display: flex;
      align-items: center;
      justify-content: space-between;
      width: 100%;
      padding: 0 4px;
    }

    .light-badge {
      display: inline-flex;
      align-items: center;
      gap: 6px;
      background: rgba(255, 215, 0, 0.16);
      border: 1px solid rgba(255, 215, 0, 0.45);
      color: #fef08a;
      font-size: 12px;
      font-weight: 700;
      padding: 4px 10px;
      border-radius: 999px;
      text-shadow: 0 0 8px rgba(255, 215, 0, 0.4);
    }

    .light-rays {
      display: flex;
      align-items: center;
      gap: 4px;
      color: #fde047;
      font-size: 12px;
      font-weight: 600;
      letter-spacing: 0.5px;
    }

    .scene-container {
      position: relative;
      width: 100%;
      display: flex;
      align-items: flex-end;
      justify-content: space-between;
      padding: 12px 4px 8px;
      gap: 6px;
    }

    /* Light ray background lines */
    .ray-stream {
      position: absolute;
      top: 15%;
      left: 0;
      width: 100%;
      height: 70%;
      pointer-events: none;
      opacity: 0.25;
      background: repeating-linear-gradient(
        180deg,
        transparent,
        transparent 20px,
        rgba(255, 220, 100, 0.2) 20px,
        rgba(255, 220, 100, 0.2) 22px
      );
    }

    .body-column {
      display: flex;
      flex-direction: column;
      align-items: center;
      text-align: center;
      z-index: 1;
      flex: 1 1 0;
      min-width: 0;
      padding: 0 2px;
    }

    .sphere-wrapper {
      position: relative;
      display: flex;
      align-items: center;
      justify-content: center;
      margin-bottom: 8px;
    }

    /* Sun */
    .sun-sphere {
      width: 110px;
      height: 110px;
      border-radius: 50%;
      background: radial-gradient(circle at 35% 35%, #fffde6 0%, #ffd043 35%, #ff7b00 75%, #cf4000 100%);
      box-shadow: 
        0 0 20px rgba(255, 170, 0, 0.7),
        0 0 45px rgba(255, 100, 0, 0.35),
        inset -6px -6px 16px rgba(150, 30, 0, 0.6);
      position: relative;
    }

    /* Earth */
    .earth-sphere {
      width: 82px;
      height: 82px;
      border-radius: 50%;
      position: relative;
      overflow: hidden;
      background: #1a5298;
      box-shadow: 0 0 14px rgba(56, 189, 248, 0.3);
    }

    .earth-continents {
      position: absolute;
      inset: 0;
      border-radius: 50%;
      background: 
        radial-gradient(ellipse at 35% 45%, #2e8b57 15%, transparent 35%),
        radial-gradient(ellipse at 70% 30%, #3cb371 18%, transparent 40%),
        radial-gradient(ellipse at 60% 75%, #2e8b57 12%, transparent 30%),
        radial-gradient(circle at 45% 60%, rgba(255, 255, 255, 0.4) 8%, transparent 20%);
    }

    .earth-clouds {
      position: absolute;
      inset: 0;
      border-radius: 50%;
      background: 
        radial-gradient(ellipse at 30% 25%, rgba(255, 255, 255, 0.7) 10%, transparent 28%),
        radial-gradient(ellipse at 65% 55%, rgba(255, 255, 255, 0.6) 15%, transparent 32%),
        radial-gradient(ellipse at 40% 80%, rgba(255, 255, 255, 0.65) 12%, transparent 25%);
    }

    /* Moon */
    .moon-sphere {
      width: 56px;
      height: 56px;
      border-radius: 50%;
      position: relative;
      overflow: hidden;
      background: #94a3b8;
      box-shadow: 0 0 10px rgba(226, 232, 240, 0.25);
    }

    .moon-craters {
      position: absolute;
      inset: 0;
      border-radius: 50%;
      background: 
        radial-gradient(circle at 35% 35%, #525a66 10%, transparent 14%),
        radial-gradient(circle at 60% 30%, #47505d 8%, transparent 12%),
        radial-gradient(circle at 45% 65%, #3d4653 12%, transparent 16%),
        radial-gradient(circle at 70% 60%, #525a66 7%, transparent 11%),
        radial-gradient(circle at 30% 70%, #47505d 6%, transparent 10%);
    }

    /* 3D Sphere Shading Overlay */
    .sphere-shading {
      position: absolute;
      inset: 0;
      border-radius: 50%;
      pointer-events: none;
      background: radial-gradient(circle at 25% 30%, rgba(255, 255, 255, 0.4) 0%, rgba(255, 255, 255, 0) 38%, rgba(0, 0, 0, 0.78) 82%, rgba(0, 0, 0, 0.98) 100%);
    }

    .sun-shading {
      position: absolute;
      inset: 0;
      border-radius: 50%;
      pointer-events: none;
      background: radial-gradient(circle at 35% 35%, rgba(255, 255, 255, 0.45) 0%, rgba(255, 255, 255, 0) 55%, rgba(180, 40, 0, 0.4) 100%);
    }

    .body-name {
      font-size: 15px;
      font-weight: 700;
      color: #ffffff;
      margin-bottom: 4px;
      letter-spacing: 0.3px;
    }

    .shape-badge {
      display: flex;
      flex-direction: column;
      align-items: center;
      justify-content: center;
      background: rgba(30, 41, 59, 0.85);
      border: 1px solid rgba(255, 255, 255, 0.25);
      color: #ffffff;
      font-size: 11px;
      font-weight: 600;
      line-height: 1.25;
      padding: 3px 6px;
      border-radius: 6px;
      width: 100%;
      max-width: 115px;
      box-shadow: 0 2px 4px rgba(0, 0, 0, 0.3);
    }

    .shape-badge span.badge-sub {
      color: #cbd5e1;
      font-weight: 500;
      font-size: 10px;
    }

    .controls-bar {
      display: flex;
      align-items: center;
      justify-content: center;
      gap: 10px;
      width: 100%;
      max-width: 400px;
      padding: 6px 14px;
      background: rgba(30, 41, 59, 0.7);
      border: 1px solid rgba(255, 255, 255, 0.2);
      border-radius: 999px;
    }

    .controls-bar label {
      font-size: 12px;
      color: #f8fafc;
      font-weight: 600;
      white-space: nowrap;
      cursor: pointer;
    }

    .range-slider {
      flex: 1;
      accent-color: #ffd700;
      cursor: pointer;
      height: 6px;
    }

    @media (max-width: 420px) {
      .sun-sphere { width: 84px; height: 84px; }
      .earth-sphere { width: 62px; height: 62px; }
      .moon-sphere { width: 42px; height: 42px; }
      .body-name { font-size: 13px; margin-bottom: 3px; }
      .shape-badge { font-size: 10px; padding: 2px 4px; }
      .shape-badge span.badge-sub { font-size: 9px; }
      .light-badge { font-size: 11px; padding: 3px 8px; }
      .light-rays { font-size: 11px; }
      .controls-bar { padding: 4px 10px; gap: 8px; }
      .controls-bar label { font-size: 11px; }
    }

    @media (max-width: 340px) {
      .sun-sphere { width: 72px; height: 72px; }
      .earth-sphere { width: 54px; height: 54px; }
      .moon-sphere { width: 36px; height: 36px; }
      .shape-badge { font-size: 9.5px; }
    }
  </style>
</head>
<body>

  <div class="main-wrapper">
    <div class="header-bar">
      <div class="light-badge">
        <span>☀ Light Source (Left)</span>
      </div>
      <div class="light-rays">
        <span>Rays →</span>
      </div>
    </div>

    <div class="scene-container">
      <div class="ray-stream"></div>

      
      <div class="body-column">
        <div class="sphere-wrapper">
          <div class="sun-sphere">
            <div class="sun-shading" id="sunShade"></div>
          </div>
        </div>
        <div class="body-name">Sun</div>
        <div class="shape-badge">
          <span>Shape: Sphere</span>
          <span class="badge-sub">(Ball)</span>
        </div>
      </div>

      
      <div class="body-column">
        <div class="sphere-wrapper">
          <div class="earth-sphere">
            <div class="earth-continents"></div>
            <div class="earth-clouds"></div>
            <div class="sphere-shading" id="earthShade"></div>
          </div>
        </div>
        <div class="body-name">Earth</div>
        <div class="shape-badge">
          <span>Shape: Sphere</span>
          <span class="badge-sub">(Ball)</span>
        </div>
      </div>

      
      <div class="body-column">
        <div class="sphere-wrapper">
          <div class="moon-sphere">
            <div class="moon-craters"></div>
            <div class="sphere-shading" id="moonShade"></div>
          </div>
        </div>
        <div class="body-name">Moon</div>
        <div class="shape-badge">
          <span>Shape: Sphere</span>
          <span class="badge-sub">(Ball)</span>
        </div>
      </div>
    </div>

    <div class="controls-bar">
      <label for="lightAngle">Light Angle</label>
      <input type="range" id="lightAngle" class="range-slider" min="15" max="65" value="25" aria-label="Adjust Light Angle">
    </div>
  </div>

  <script>
    const slider = document.getElementById('lightAngle');
    const earthShade = document.getElementById('earthShade');
    const moonShade = document.getElementById('moonShade');

    slider.addEventListener('input', (e) => {
      const x = e.target.value;
      const y = Math.max(20, Math.min(50, x * 1.1));
      const grad = `radial-gradient(circle at ${x}% ${y}%, rgba(255, 255, 255, 0.4) 0%, rgba(255, 255, 255, 0) 38%, rgba(0, 0, 0, 0.78) 82%, rgba(0, 0, 0, 0.98) 100%)`;
      earthShade.style.background = grad;
      moonShade.style.background = grad;
    });
  </script>
</body>
</html>

Spherical Bodies in the Solar System

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <meta name="aspect-ratio" content="4:3">
  <style>
    * { box-sizing: border-box; margin: 0; padding: 0; font-family: system-ui, -apple-system, sans-serif; }
    body {
      background: #f8fafc;
      color: #1e2945;
      padding: 12px;
      display: flex;
      flex-direction: column;
      gap: 10px;
      user-select: none;
    }

    /* Controls Bar */
    .controls {
      display: flex;
      align-items: center;
      justify-content: space-between;
      gap: 8px;
      background: #ffffff;
      padding: 8px 12px;
      border-radius: 12px;
      border: 1px solid #e2e8f0;
    }
    .btn-group {
      display: flex;
      gap: 6px;
    }
    .btn {
      background: #f1f5f9;
      border: 1px solid #cbd5e1;
      color: #334155;
      padding: 6px 12px;
      border-radius: 8px;
      font-size: 13px;
      font-weight: 600;
      cursor: pointer;
      transition: all 0.2s ease;
    }
    .btn.active {
      background: #22b7ff;
      border-color: #0ea5e9;
      color: #ffffff;
    }
    .play-btn {
      width: 34px;
      height: 34px;
      display: flex;
      align-items: center;
      justify-content: center;
      padding: 0;
      font-size: 14px;
    }
    .slider-wrap {
      display: flex;
      align-items: center;
      gap: 8px;
      flex: 1;
      max-width: 180px;
    }
    .slider-wrap input {
      width: 100%;
      accent-color: #22b7ff;
      cursor: pointer;
    }

    /* Comparison Rows */
    .row-card {
      background: #ffffff;
      border: 1px solid #e2e8f0;
      border-radius: 12px;
      padding: 10px 14px;
      display: grid;
      grid-template-columns: 100px 1fr 110px;
      align-items: center;
      gap: 12px;
      min-height: 105px;
    }
    .label-col {
      display: flex;
      flex-direction: column;
      gap: 4px;
    }
    .title {
      font-size: 14px;
      font-weight: 700;
      color: #0f172a;
    }
    .badge {
      display: inline-flex;
      align-items: center;
      gap: 4px;
      font-size: 12px;
      font-weight: 700;
      padding: 2px 6px;
      border-radius: 6px;
      width: fit-content;
    }
    .badge-cross {
      background: #fee2e2;
      color: #dc2626;
    }
    .badge-check {
      background: #dcfce7;
      color: #16a34a;
    }

    /* Viewport / 3D Space */
    .stage {
      height: 90px;
      display: flex;
      align-items: center;
      justify-content: center;
      perspective: 400px;
      position: relative;
    }

    /* Disc Moon */
    .disc-moon {
      width: 76px;
      height: 76px;
      border-radius: 50%;
      background: #cbd5e1;
      position: relative;
      transform-style: preserve-3d;
      box-shadow: 0 4px 12px rgba(0,0,0,0.08);
      transition: transform 0.1s linear;
    }
    .disc-surface {
      position: absolute;
      inset: 0;
      border-radius: 50%;
      background: radial-gradient(circle at 35% 35%, #f1f5f9 0%, #cbd5e1 70%, #94a3b8 100%);
      overflow: hidden;
      border: 1px solid #94a3b8;
    }

    /* Sphere Moon */
    .sphere-moon {
      width: 76px;
      height: 76px;
      border-radius: 50%;
      position: relative;
      overflow: hidden;
      border: 1px solid #94a3b8;
      box-shadow: 0 4px 12px rgba(0,0,0,0.08);
      background: #cbd5e1;
    }
    .sphere-texture {
      position: absolute;
      width: 150px;
      height: 76px;
      left: 0;
      top: 0;
      display: flex;
      align-items: center;
      transition: transform 0.1s linear;
    }
    .sphere-shade {
      position: absolute;
      inset: 0;
      border-radius: 50%;
      background: radial-gradient(circle at 30% 30%, rgba(255,255,255,0.7) 0%, rgba(255,255,255,0) 45%, rgba(15,23,42,0.45) 100%);
      pointer-events: none;
    }

    /* Craters */
    .crater {
      position: absolute;
      border-radius: 50%;
      background: #94a3b8;
      border: 1px solid #64748b;
      opacity: 0.8;
    }

    /* Result State Tag */
    .status-col {
      text-align: right;
      font-size: 13px;
      font-weight: 600;
    }
    .status-cross { color: #dc2626; }
    .status-check { color: #16a34a; }

    /* Conclusion Banner */
    .banner {
      background: #e0f2fe;
      border: 1px solid #7dd3fc;
      color: #0369a1;
      padding: 8px 12px;
      border-radius: 10px;
      font-size: 13px;
      font-weight: 700;
      text-align: center;
      display: flex;
      align-items: center;
      justify-content: center;
      gap: 6px;
    }

    @media (max-width: 420px) {
      .row-card {
        grid-template-columns: 80px 1fr 90px;
        padding: 8px;
        gap: 6px;
      }
      .disc-moon, .sphere-moon {
        width: 64px;
        height: 64px;
      }
      .sphere-texture {
        height: 64px;
        width: 130px;
      }
      .title { font-size: 13px; }
      .status-col { font-size: 12px; }
      .slider-wrap { max-width: 110px; }
    }
  </style>
</head>
<body>

  
  <div class="controls">
    <button id="playBtn" class="btn play-btn" title="Toggle Auto Tilt">⏸</button>
    <div class="btn-group">
      <button class="btn active" data-angle="0">0°</button>
      <button class="btn" data-angle="45">45°</button>
      <button class="btn" data-angle="85">85°</button>
    </div>
    <div class="slider-wrap">
      <input type="range" id="angleSlider" min="0" max="85" value="0">
    </div>
  </div>

  
  <div class="row-card">
    <div class="label-col">
      <span class="title">Flat Disc</span>
      <span class="badge badge-cross">❌ False</span>
    </div>
    <div class="stage">
      <div id="discMoon" class="disc-moon">
        <div class="disc-surface">
          <div class="crater" style="top:18%; left:22%; width:16px; height:16px;"></div>
          <div class="crater" style="top:52%; left:55%; width:22px; height:22px;"></div>
          <div class="crater" style="top:58%; left:25%; width:12px; height:12px;"></div>
          <div class="crater" style="top:25%; left:62%; width:10px; height:10px;"></div>
        </div>
      </div>
    </div>
    <div id="discStatus" class="status-col status-cross">
      Turns into<br>sliver ❌
    </div>
  </div>

  
  <div class="row-card">
    <div class="label-col">
      <span class="title">Sphere</span>
      <span class="badge badge-check">✓ Real Moon</span>
    </div>
    <div class="stage">
      <div class="sphere-moon">
        <div id="sphereTexture" class="sphere-texture">
          <div class="crater" style="top:18%; left:22px; width:16px; height:16px;"></div>
          <div class="crater" style="top:52%; left:55px; width:22px; height:22px;"></div>
          <div class="crater" style="top:58%; left:25px; width:12px; height:12px;"></div>
          <div class="crater" style="top:25%; left:62px; width:10px; height:10px;"></div>
          
          <div class="crater" style="top:22%; left:95px; width:14px; height:14px;"></div>
          <div class="crater" style="top:50%; left:125px; width:18px; height:18px;"></div>
        </div>
        <div class="sphere-shade"></div>
      </div>
    </div>
    <div class="status-col status-check">
      Always looks<br>round ✓
    </div>
  </div>

  
  <div class="banner">
    <span>✦</span> Always looks round = Must be a Sphere! <span>✓</span>
  </div>

  <script>
    const slider = document.getElementById('angleSlider');
    const playBtn = document.getElementById('playBtn');
    const discMoon = document.getElementById('discMoon');
    const sphereTexture = document.getElementById('sphereTexture');
    const discStatus = document.getElementById('discStatus');
    const presetBtns = document.querySelectorAll('.btn-group .btn');

    let isPlaying = true;
    let angle = 0;
    let direction = 1;
    let animTimer = null;

    function updateVisuals(deg) {
      angle = deg;
      slider.value = deg;

      // Rotate flat disc in 3D
      discMoon.style.transform = `rotateY(${deg}deg)`;

      // Move sphere surface craters across outline (silhouette stays 100% round)
      const maxShift = 45;
      const shiftX = -(deg / 85) * maxShift;
      sphereTexture.style.transform = `translateX(${shiftX}px)`;

      // Update disc label based on tilt
      if (deg > 60) {
        discStatus.innerHTML = "Thin edge<br>sliver ❌";
      } else if (deg > 25) {
        discStatus.innerHTML = "Squashed<br>oval ❌";
      } else {
        discStatus.innerHTML = "Round only<br>face-on";
      }

      // Update active preset button highlight
      presetBtns.forEach(btn => {
        const btnAngle = parseInt(btn.dataset.angle);
        btn.classList.toggle('active', Math.abs(btnAngle - deg) < 5);
      });
    }

    function stepAnimation() {
      if (!isPlaying) return;
      angle += direction * 0.75;
      if (angle >= 85) {
        angle = 85;
        direction = -1;
      } else if (angle <= 0) {
        angle = 0;
        direction = 1;
      }
      updateVisuals(angle);
    }

    animTimer = setInterval(stepAnimation, 25);

    function pause() {
      isPlaying = false;
      playBtn.textContent = '▶';
    }

    function play() {
      isPlaying = true;
      playBtn.textContent = '⏸';
    }

    playBtn.addEventListener('click', () => {
      if (isPlaying) pause();
      else play();
    });

    slider.addEventListener('input', (e) => {
      pause();
      updateVisuals(parseFloat(e.target.value));
    });

    presetBtns.forEach(btn => {
      btn.addEventListener('click', () => {
        pause();
        updateVisuals(parseFloat(btn.dataset.angle));
      });
    });

    updateVisuals(0);
  </script>
</body>
</html>

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <meta name="aspect-ratio" content="4:3">
  <title>Terminator Line: Flat Disc vs 3D Sphere</title>
  <style>
    * {
      box-sizing: border-box;
      margin: 0;
      padding: 0;
    }

    body {
      font-family: system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, sans-serif;
      background: #0f172a;
      color: #f8fafc;
      width: 100%;
      min-height: 100%;
      display: flex;
      flex-direction: column;
      align-items: center;
      justify-content: space-between;
      padding: 12px;
      user-select: none;
    }

    .diagram-grid {
      display: grid;
      grid-template-columns: 1fr 1fr;
      gap: 12px;
      width: 100%;
      max-width: 600px;
      flex: 1;
    }

    @media (max-width: 440px) {
      .diagram-grid {
        grid-template-columns: 1fr 1fr;
        gap: 8px;
      }
    }

    .panel {
      background: #1e293b;
      border-radius: 12px;
      padding: 10px 8px;
      display: flex;
      flex-direction: column;
      align-items: center;
      justify-content: space-between;
      border: 1px solid #334155;
    }

    .panel-title {
      font-size: 14px;
      font-weight: 700;
      text-align: center;
      line-height: 1.2;
    }

    .title-flat { color: #cbd5e1; }
    .title-sphere { color: #38bdf8; }

    .panel-subtitle {
      font-size: 12px;
      font-weight: 500;
      color: #94a3b8;
      margin-top: 2px;
    }

    .svg-container {
      width: 100%;
      max-width: 200px;
      aspect-ratio: 1 / 1;
      display: flex;
      align-items: center;
      justify-content: center;
      margin: 6px 0;
    }

    svg {
      width: 100%;
      height: 100%;
      overflow: visible;
    }

    .controls {
      width: 100%;
      max-width: 480px;
      background: #1e293b;
      border: 1px solid #334155;
      border-radius: 10px;
      padding: 8px 14px;
      display: flex;
      flex-direction: column;
      gap: 6px;
      margin-top: 8px;
    }

    .slider-row {
      display: flex;
      align-items: center;
      justify-content: space-between;
      font-size: 13px;
      font-weight: 600;
      color: #f8fafc;
    }

    .sun-tag {
      color: #fbbf24;
      display: flex;
      align-items: center;
      gap: 4px;
    }

    input[type="range"] {
      -webkit-appearance: none;
      appearance: none;
      width: 100%;
      height: 6px;
      border-radius: 3px;
      background: #334155;
      outline: none;
      cursor: pointer;
    }

    input[type="range"]::-webkit-slider-thumb {
      -webkit-appearance: none;
      appearance: none;
      width: 18px;
      height: 18px;
      border-radius: 50%;
      background: #fbbf24;
      box-shadow: 0 0 8px rgba(251, 191, 36, 0.6);
      cursor: pointer;
    }

    input[type="range"]::-moz-range-thumb {
      width: 18px;
      height: 18px;
      border-radius: 50%;
      background: #fbbf24;
      border: none;
      box-shadow: 0 0 8px rgba(251, 191, 36, 0.6);
      cursor: pointer;
    }
  </style>
</head>
<body>

  <div class="diagram-grid">
    
    <div class="panel">
      <div>
        <div class="panel-title title-flat">Flat Disc</div>
        <div class="panel-subtitle">Straight Shadow Edge</div>
      </div>
      <div class="svg-container">
        <svg viewBox="0 0 200 200">
          <defs>
            <clipPath id="discClip">
              <circle cx="100" cy="100" r="75" />
            </clipPath>
          </defs>

          
          <circle cx="100" cy="100" r="75" fill="#0f172a" stroke="#475569" stroke-width="2"/>
          
          
          <g clip-path="url(#discClip)">
            <rect id="flatLitRect" x="25" y="25" width="75" height="150" fill="#e2e8f0" />
            
            <circle cx="100" cy="100" r="74" fill="none" stroke="#64748b" stroke-width="1.5" opacity="0.4"/>
          </g>

          
          <line id="flatLine" x1="100" y1="25" x2="100" y2="175" stroke="#fbbf24" stroke-width="2.5" stroke-dasharray="4 2" />
        </svg>
      </div>
    </div>

    
    <div class="panel">
      <div>
        <div class="panel-title title-sphere">3D Sphere</div>
        <div class="panel-subtitle">Curved Terminator Line</div>
      </div>
      <div class="svg-container">
        <svg viewBox="0 0 200 200">
          <defs>
            <radialGradient id="sphereShadow" cx="50%" cy="50%" r="50%">
              <stop offset="60%" stop-color="#000000" stop-opacity="0" />
              <stop offset="100%" stop-color="#000000" stop-opacity="0.7" />
            </radialGradient>
            <clipPath id="sphereClip">
              <circle cx="100" cy="100" r="75" />
            </clipPath>
          </defs>

          
          <circle cx="100" cy="100" r="75" fill="#0f172a" stroke="#334155" stroke-width="1.5"/>

          
          <g clip-path="url(#sphereClip)">
            <path id="sphereLitPath" d="" fill="#f1f5f9" />
            
            
            <g opacity="0.12" fill="#334155">
              <ellipse cx="85" cy="80" rx="14" ry="10" />
              <ellipse cx="115" cy="70" rx="18" ry="14" />
              <ellipse cx="95" cy="120" rx="20" ry="12" />
              <circle cx="125" cy="115" r="9" />
            </g>

            
            <circle cx="100" cy="100" r="75" fill="url(#sphereShadow)" />
          </g>

          
          <path id="terminatorCurve" d="" fill="none" stroke="#38bdf8" stroke-width="2.5" />
        </svg>
      </div>
    </div>
  </div>

  
  <div class="controls">
    <div class="slider-row">
      <span class="sun-tag">☀️ Sunlight Angle</span>
      <span id="angleValue" style="color:#94a3b8; font-size:12px;">Left 45°</span>
    </div>
    <input type="range" id="angleSlider" min="-75" max="75" value="-45" step="1">
  </div>

  <script>
    const slider = document.getElementById('angleSlider');
    const flatLitRect = document.getElementById('flatLitRect');
    const flatLine = document.getElementById('flatLine');
    const sphereLitPath = document.getElementById('sphereLitPath');
    const terminatorCurve = document.getElementById('terminatorCurve');
    const angleValue = document.getElementById('angleValue');

    const CX = 100;
    const CY = 100;
    const R = 75;

    function update(angle) {
      // Label
      const side = angle < 0 ? 'Left' : (angle > 0 ? 'Right' : 'Center');
      angleValue.textContent = `${side} ${Math.abs(angle)}°`;

      // Normalized ratio [-1, 1]
      const t = angle / 75; 

      // 1. Flat Disc Update (Straight Edge translation)
      const flatX = CX + t * (R * 0.75);
      if (angle < 0) {
        flatLitRect.setAttribute('x', 25);
        flatLitRect.setAttribute('width', Math.max(0, flatX - 25));
      } else {
        flatLitRect.setAttribute('x', flatX);
        flatLitRect.setAttribute('width', Math.max(0, 175 - flatX));
      }
      flatLine.setAttribute('x1', flatX);
      flatLine.setAttribute('x2', flatX);

      // 2. 3D Sphere Update (Curved Terminator Line)
      // On an orthographic sphere, terminator curves as a 3D ellipse:
      // semi-minor horizontal radius rx = R * sin(phase)
      const rad = (angle * Math.PI) / 180;
      const rx = Math.abs(R * Math.sin(rad));
      
      let litD = '';
      let termD = '';

      if (angle < 0) {
        // Lit from Left
        // Outer arc is left half of circle: from (100, 25) counterclockwise to (100, 175)
        // Terminator connects (100, 175) back to (100, 25)
        const sweep = angle < -40 ? 0 : 1; 
        litD = `M 100,25 A 75 75 0 0 0 100,175 A ${rx} 75 0 0 ${sweep} 100,25 Z`;
        termD = `M 100,25 A ${rx} 75 0 0 ${sweep === 1 ? 0 : 1} 100,175`;
      } else if (angle > 0) {
        // Lit from Right
        // Outer arc is right half of circle: from (100, 25) clockwise to (100, 175)
        const sweep = angle > 40 ? 0 : 1;
        litD = `M 100,25 A 75 75 0 0 1 100,175 A ${rx} 75 0 0 ${sweep} 100,25 Z`;
        termD = `M 100,25 A ${rx} 75 0 0 ${sweep === 1 ? 0 : 1} 100,175`;
      } else {
        // Exactly half lit
        litD = `M 100,25 A 75 75 0 0 0 100,175 L 100,25 Z`;
        termD = `M 100,25 L 100,175`;
      }

      sphereLitPath.setAttribute('d', litD);
      terminatorCurve.setAttribute('d', termD);
    }

    slider.addEventListener('input', (e) => {
      update(parseInt(e.target.value, 10));
    });

    // Initial render
    update(parseInt(slider.value, 10));
  </script>
</body>
</html>

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <meta name="aspect-ratio" content="4:3">
  <title>Ship Horizon Evidence</title>
  <style>
    * { box-sizing: border-box; margin: 0; padding: 0; }
    body {
      font-family: system-ui, -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif;
      background: #f8fafc;
      color: #1e293b;
      padding: 8px;
      display: flex;
      flex-direction: column;
      gap: 8px;
      user-select: none;
      -webkit-user-select: none;
    }

    .track-card {
      background: #ffffff;
      border: 1px solid #e2e8f0;
      border-radius: 8px;
      padding: 6px 8px;
      display: flex;
      flex-direction: column;
      gap: 4px;
    }

    .track-header {
      display: flex;
      justify-content: space-between;
      align-items: center;
      font-size: 13px;
      font-weight: 700;
    }

    .badge {
      display: inline-flex;
      align-items: center;
      gap: 4px;
      padding: 2px 8px;
      border-radius: 12px;
      font-size: 12px;
    }
    .badge-spherical { background: #e0f2fe; color: #0369a1; }
    .badge-flat { background: #f1f5f9; color: #475569; }

    .track-content {
      display: grid;
      grid-template-columns: 1fr 100px;
      gap: 8px;
      align-items: center;
    }

    .svg-container {
      width: 100%;
      height: 110px;
      background: #f0f9ff;
      border-radius: 6px;
      overflow: hidden;
      border: 1px solid #e2e8f0;
    }

    .scope-box {
      display: flex;
      flex-direction: column;
      align-items: center;
      gap: 2px;
    }

    .scope-title {
      font-size: 11px;
      font-weight: 600;
      color: #64748b;
      text-transform: uppercase;
      letter-spacing: 0.5px;
    }

    .scope-lens {
      width: 86px;
      height: 86px;
      border-radius: 50%;
      border: 3px solid #334155;
      overflow: hidden;
      position: relative;
      background: #bae6fd;
      box-shadow: inset 0 0 8px rgba(0,0,0,0.25);
    }

    .controls-panel {
      background: #ffffff;
      border: 1px solid #e2e8f0;
      border-radius: 8px;
      padding: 8px 12px;
      display: flex;
      flex-wrap: wrap;
      align-items: center;
      justify-content: space-between;
      gap: 8px;
    }

    .slider-group {
      display: flex;
      align-items: center;
      gap: 8px;
      flex: 1;
      min-width: 180px;
    }

    .slider-label {
      font-size: 12px;
      font-weight: 700;
      color: #475569;
      white-space: nowrap;
    }

    input[type=range] {
      flex: 1;
      height: 6px;
      border-radius: 3px;
      background: #cbd5e1;
      outline: none;
      accent-color: #0284c7;
      cursor: pointer;
    }

    .btn-group {
      display: flex;
      gap: 4px;
    }

    button {
      background: #f1f5f9;
      border: 1px solid #cbd5e1;
      border-radius: 6px;
      padding: 4px 10px;
      font-size: 12px;
      font-weight: 600;
      color: #334155;
      cursor: pointer;
      display: inline-flex;
      align-items: center;
      justify-content: center;
      gap: 4px;
    }

    button:hover { background: #e2e8f0; }
    button.active {
      background: #0284c7;
      border-color: #0284c7;
      color: #ffffff;
    }

    @media (max-width: 480px) {
      .track-content {
        grid-template-columns: 1fr 84px;
        gap: 6px;
      }
      .svg-container { height: 95px; }
      .scope-lens { width: 72px; height: 72px; }
    }
  </style>
</head>
<body>

  
  <div class="track-card">
    <div class="track-header">
      <span class="badge badge-spherical">● Spherical Earth</span>
      <span style="font-size: 11px; color: #64748b;">Curved Horizon</span>
    </div>
    <div class="track-content">
      <div class="svg-container">
        <svg id="svgSphereSide" viewBox="0 0 360 110" width="100%" height="100%">
          
          <defs>
            <linearGradient id="skyGrad" x1="0" y1="0" x2="0" y2="1">
              <stop offset="0%" stop-color="#bae6fd" />
              <stop offset="100%" stop-color="#e0f2fe" />
            </linearGradient>
            
            <g id="boatShape">
              
              <path d="M -15,-1 L 15,-1 L 11,-7 L -11,-7 Z" fill="#854d0e" stroke="#451a03" stroke-width="0.8"/>
              
              <line x1="0" y1="-7" x2="0" y2="-25" stroke="#334155" stroke-width="1.5" stroke-linecap="round"/>
              
              <path d="M 1,-8 L 1,-23 L 13,-11 Z" fill="#ffffff" stroke="#cbd5e1" stroke-width="0.8"/>
              
              <path d="M -1,-8 L -1,-20 L -10,-9 Z" fill="#f8fafc" stroke="#cbd5e1" stroke-width="0.8"/>
              
              <path d="M 0,-25 L 5,-23 L 0,-21 Z" fill="#ef4444"/>
            </g>
          </defs>

          <rect width="360" height="110" fill="url(#skyGrad)"/>

          
          <line id="sphereRay" x1="28" y1="46" x2="350" y2="76" stroke="#94a3b8" stroke-width="1.2" stroke-dasharray="3,3"/>

          
          <g id="sphereSideShip" transform="translate(60, 58)">
            <use href="#boatShape" />
          </g>

          
          <path d="M 0,72 Q 130,55 360,105 L 360,110 L 0,110 Z" fill="#0284c7"/>
          <path d="M 0,72 Q 130,55 360,105" fill="none" stroke="#38bdf8" stroke-width="1.5"/>

          
          <g transform="translate(24, 45)">
            <circle cx="0" cy="0" r="3.5" fill="#1e293b"/>
            <line x1="0" y1="3.5" x2="0" y2="16" stroke="#1e293b" stroke-width="2.5"/>
            <path d="M 0,16 L -3,27 M 0,16 L 3,27" stroke="#1e293b" stroke-width="2"/>
            
            <path d="M 0,7 L 6,6 L 9,5" stroke="#0f172a" stroke-width="2.5" stroke-linecap="round"/>
          </g>
        </svg>
      </div>

      
      <div class="scope-box">
        <span class="scope-title">Observer View</span>
        <div class="scope-lens">
          <svg viewBox="0 0 100 100" width="100%" height="100%">
            
            <rect width="100" height="50" fill="#bae6fd"/>
            
            <line x1="0" y1="50" x2="100" y2="50" stroke="rgba(255,255,255,0.4)" stroke-width="1"/>
            <line x1="50" y1="0" x2="50" y2="100" stroke="rgba(255,255,255,0.2)" stroke-width="1"/>
            
            
            <g id="sphereScopeShip" transform="translate(50, 50) scale(1)">
              <use href="#boatShape" />
            </g>

            
            <rect x="0" y="50" width="100" height="50" fill="#0284c7"/>
            <line x1="0" y1="50" x2="100" y2="50" stroke="#38bdf8" stroke-width="1.5"/>

            
            <circle cx="50" cy="50" r="46" fill="none" stroke="rgba(0,0,0,0.3)" stroke-width="4"/>
          </svg>
        </div>
      </div>
    </div>
  </div>

  
  <div class="track-card">
    <div class="track-header">
      <span class="badge badge-flat">● Flat Earth</span>
      <span style="font-size: 11px; color: #64748b;">Flat Plane</span>
    </div>
    <div class="track-content">
      <div class="svg-container">
        <svg id="svgFlatSide" viewBox="0 0 360 110" width="100%" height="100%">
          <rect width="360" height="110" fill="url(#skyGrad)"/>

          
          <line id="flatRay" x1="28" y1="50" x2="350" y2="70" stroke="#94a3b8" stroke-width="1.2" stroke-dasharray="3,3"/>

          
          <rect x="0" y="70" width="360" height="40" fill="#0284c7"/>
          <line x1="0" y1="70" x2="360" y2="70" stroke="#38bdf8" stroke-width="1.5"/>

          
          <g id="flatSideShip" transform="translate(60, 70)">
            <use href="#boatShape" />
          </g>

          
          <g transform="translate(24, 45)">
            <circle cx="0" cy="0" r="3.5" fill="#1e293b"/>
            <line x1="0" y1="3.5" x2="0" y2="16" stroke="#1e293b" stroke-width="2.5"/>
            <path d="M 0,16 L -3,25 M 0,16 L 3,25" stroke="#1e293b" stroke-width="2"/>
            <path d="M 0,7 L 6,6 L 9,5" stroke="#0f172a" stroke-width="2.5" stroke-linecap="round"/>
          </g>
        </svg>
      </div>

      
      <div class="scope-box">
        <span class="scope-title">Observer View</span>
        <div class="scope-lens">
          <svg viewBox="0 0 100 100" width="100%" height="100%">
            
            <rect width="100" height="50" fill="#bae6fd"/>
            <line x1="0" y1="50" x2="100" y2="50" stroke="rgba(255,255,255,0.4)" stroke-width="1"/>
            <line x1="50" y1="0" x2="50" y2="100" stroke="rgba(255,255,255,0.2)" stroke-width="1"/>

            
            <rect x="0" y="50" width="100" height="50" fill="#0284c7"/>
            <line x1="0" y1="50" x2="100" y2="50" stroke="#38bdf8" stroke-width="1.5"/>

            
            <g id="flatScopeShip" transform="translate(50, 50) scale(1)">
              <use href="#boatShape" />
            </g>

            <circle cx="50" cy="50" r="46" fill="none" stroke="rgba(0,0,0,0.3)" stroke-width="4"/>
          </svg>
        </div>
      </div>
    </div>
  </div>

  
  <div class="controls-panel">
    <button id="playBtn" style="min-width: 72px;">▶ Play</button>
    <div class="slider-group">
      <span class="slider-label">Distance:</span>
      <input type="range" id="distSlider" min="0" max="100" value="0" />
    </div>
    <div class="btn-group">
      <button class="active" id="btnNear">Near</button>
      <button id="btnMid">Mid</button>
      <button id="btnFar">Far</button>
    </div>
  </div>

  <script>
    const slider = document.getElementById('distSlider');
    const playBtn = document.getElementById('playBtn');
    const btnNear = document.getElementById('btnNear');
    const btnMid = document.getElementById('btnMid');
    const btnFar = document.getElementById('btnFar');

    const sphereSideShip = document.getElementById('sphereSideShip');
    const sphereScopeShip = document.getElementById('sphereScopeShip');
    const flatSideShip = document.getElementById('flatSideShip');
    const flatScopeShip = document.getElementById('flatScopeShip');
    const sphereRay = document.getElementById('sphereRay');
    const flatRay = document.getElementById('flatRay');

    let isPlaying = false;
    let animProgress = 0;
    let animDir = 1;
    let animFrame = null;

    function updateScene(t) {
      // t is normalized distance: 0 (Near) to 1 (Far)
      
      // 1. SPHERICAL SIDE VIEW
      // Ocean quadratic curve: peak at x=130, y=55; drops at x=340, y=100
      const startX = 60;
      const endX = 330;
      const xSphere = startX + t * (endX - startX);
      
      // Quadratic curve equation for spherical water surface
      const dx = xSphere - 130;
      const ySphere = 55 + (dx > 0 ? 0.00102 * dx * dx : 0.003 * dx * dx);
      // Tangent angle
      const slope = dx > 0 ? 2 * 0.00102 * dx : 2 * 0.003 * dx;
      const angleDeg = Math.atan(slope) * (180 / Math.PI);
      const sideScale = 1.0 - t * 0.55;

      sphereSideShip.setAttribute('transform', 
        `translate(${xSphere}, ${ySphere}) rotate(${angleDeg}) scale(${sideScale})`
      );

      // Ray target updates
      sphereRay.setAttribute('x2', Math.max(xSphere, 140));
      sphereRay.setAttribute('y2', 46 + (Math.max(xSphere, 140) - 28) * 0.095);

      // 2. SPHERICAL SCOPE VIEW
      // In telescope: boat scale shrinks, and sinks downwards behind ocean rect (y=50)
      const scopeScaleSphere = 1.0 - t * 0.6;
      // Hull height is ~7px, mast/sails is ~20px. Total ~27px.
      // Sinking profile: hull goes below first (t: 0.2->0.5), sails (t: 0.5->0.85), mast tip (t: 0.85->1.0)
      const ySink = 50 + Math.pow(t, 1.35) * (26 * scopeScaleSphere + 2);

      sphereScopeShip.setAttribute('transform',
        `translate(50, ${ySink}) scale(${scopeScaleSphere})`
      );

      // 3. FLAT SIDE VIEW
      const xFlat = 60 + t * 270;
      const yFlat = 70;
      flatSideShip.setAttribute('transform',
        `translate(${xFlat}, ${yFlat}) scale(${sideScale})`
      );
      flatRay.setAttribute('x2', xFlat);
      flatRay.setAttribute('y2', yFlat - 12 * sideScale);

      // 4. FLAT SCOPE VIEW
      // Boat rests exactly on waterline (y=50), purely scales down (100% visible)
      const scopeScaleFlat = 1.0 - t * 0.6;
      flatScopeShip.setAttribute('transform',
        `translate(50, 50) scale(${scopeScaleFlat})`
      );

      // Quick jump button active states
      btnNear.classList.toggle('active', t < 0.25);
      btnMid.classList.toggle('active', t >= 0.25 && t <= 0.75);
      btnFar.classList.toggle('active', t > 0.75);
    }

    function setDistance(val) {
      slider.value = val;
      updateScene(val / 100);
    }

    slider.addEventListener('input', (e) => {
      if (isPlaying) stopAnimation();
      updateScene(e.target.value / 100);
    });

    btnNear.addEventListener('click', () => { if (isPlaying) stopAnimation(); setDistance(0); });
    btnMid.addEventListener('click', () => { if (isPlaying) stopAnimation(); setDistance(50); });
    btnFar.addEventListener('click', () => { if (isPlaying) stopAnimation(); setDistance(100); });

    function tick() {
      animProgress += 0.004 * animDir;
      if (animProgress >= 1) {
        animProgress = 1;
        animDir = -1;
      } else if (animProgress <= 0) {
        animProgress = 0;
        animDir = 1;
      }
      slider.value = Math.round(animProgress * 100);
      updateScene(animProgress);
      if (isPlaying) {
        animFrame = requestAnimationFrame(tick);
      }
    }

    function startAnimation() {
      isPlaying = true;
      playBtn.textContent = '⏸ Pause';
      playBtn.classList.add('active');
      animProgress = slider.value / 100;
      animFrame = requestAnimationFrame(tick);
    }

    function stopAnimation() {
      isPlaying = false;
      playBtn.textContent = '▶ Play';
      playBtn.classList.remove('active');
      if (animFrame) cancelAnimationFrame(animFrame);
    }

    playBtn.addEventListener('click', () => {
      if (isPlaying) stopAnimation();
      else startAnimation();
    });

    // Initialize
    updateScene(0);
  </script>
</body>
</html>

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <meta name="aspect-ratio" content="4:3">
  <title>Planetary Feature Foreshortening</title>
  <style>
    * { box-sizing: border-box; margin: 0; padding: 0; }
    body {
      font-family: system-ui, -apple-system, sans-serif;
      background: #f8fafc;
      color: #1e2945;
      display: flex;
      flex-direction: column;
      align-items: center;
      justify-content: space-between;
      min-height: 100%;
      padding: 12px 16px;
      user-select: none;
    }

    .btn-group {
      display: flex;
      gap: 8px;
      width: 100%;
      max-width: 440px;
      justify-content: center;
      flex-wrap: wrap;
    }

    .btn {
      flex: 1 1 180px;
      padding: 8px 12px;
      font-size: 13px;
      font-weight: 600;
      border-radius: 8px;
      border: 1px solid #cbd5e1;
      background: #ffffff;
      color: #475569;
      cursor: pointer;
      display: flex;
      align-items: center;
      justify-content: center;
      gap: 6px;
      transition: background-color 0.2s, border-color 0.2s, color 0.2s, box-shadow 0.2s;
    }

    .btn.active {
      background: #0284c7;
      color: #ffffff;
      border-color: #0284c7;
      box-shadow: 0 2px 6px rgba(2, 132, 199, 0.3);
    }

    .canvas-container {
      position: relative;
      width: 100%;
      max-width: 360px;
      aspect-ratio: 1 / 1;
      display: flex;
      align-items: center;
      justify-content: center;
      margin: 6px 0;
      touch-action: none;
    }

    canvas {
      width: 100%;
      height: 100%;
      cursor: grab;
    }

    canvas:active {
      cursor: grabbing;
    }

    .controls {
      display: flex;
      flex-direction: column;
      align-items: center;
      gap: 6px;
      width: 100%;
      max-width: 320px;
    }

    .slider-row {
      display: flex;
      align-items: center;
      gap: 10px;
      width: 100%;
    }

    input[type="range"] {
      flex: 1;
      height: 6px;
      border-radius: 3px;
      background: #cbd5e1;
      outline: none;
      accent-color: #0284c7;
      cursor: pointer;
    }

    .hint {
      font-size: 12px;
      color: #64748b;
      font-weight: 500;
    }
  </style>
</head>
<body>

  <div class="btn-group">
    <button id="btnCenter" class="btn active">
      <span>⚪</span> Center: Full Circle
    </button>
    <button id="btnEdge" class="btn">
      <span>⬭</span> Edge (Limb): Foreshortened Oval
    </button>
  </div>

  <div class="canvas-container">
    <canvas id="sphereCanvas" width="720" height="720"></canvas>
  </div>

  <div class="controls">
    <div class="slider-row">
      <input type="range" id="angleSlider" min="-80" max="80" value="0" step="0.5">
    </div>
    <div class="hint">↔ Drag to rotate</div>
  </div>

  <script>
    const canvas = document.getElementById('sphereCanvas');
    const ctx = canvas.getContext('2d');
    const slider = document.getElementById('angleSlider');
    const btnCenter = document.getElementById('btnCenter');
    const btnEdge = document.getElementById('btnEdge');

    let currentAngle = 0; // degrees
    let targetAngle = 0;
    let isAnimating = false;
    let isDragging = false;
    let startX = 0;
    let startAngle = 0;

    // Fixed crater features on the sphere: [lonDeg, latDeg, radiusRatio, label]
    const features = [
      { lon: 0, lat: 0, r: 0.16, main: true },
      { lon: -55, lat: 28, r: 0.11, main: false },
      { lon: 50, lat: -25, r: 0.12, main: false },
      { lon: -110, lat: -10, r: 0.14, main: false },
      { lon: 115, lat: 30, r: 0.13, main: false },
      { lon: 180, lat: 0, r: 0.16, main: false },
      { lon: -40, lat: -45, r: 0.10, main: false },
      { lon: 45, lat: 48, r: 0.09, main: false }
    ];

    function draw() {
      const w = canvas.width;
      const h = canvas.height;
      const cx = w / 2;
      const cy = h / 2;
      const R = w * 0.38;

      ctx.clearRect(0, 0, w, h);

      // Sphere Base with 3D gradient
      const sphereGrad = ctx.createRadialGradient(cx - R * 0.25, cy - R * 0.25, R * 0.1, cx, cy, R);
      sphereGrad.addColorStop(0, '#f1f5f9');
      sphereGrad.addColorStop(0.7, '#cbd5e1');
      sphereGrad.addColorStop(1, '#94a3b8');

      ctx.save();
      ctx.beginPath();
      ctx.arc(cx, cy, R, 0, Math.PI * 2);
      ctx.fillStyle = sphereGrad;
      ctx.fill();
      ctx.clip();

      // Longitude Grid Lines (Meridians) to show sphere shape
      ctx.lineWidth = 2;
      for (let lonOffset = -180; lonOffset < 180; lonOffset += 30) {
        const netLon = ((lonOffset + currentAngle + 180) % 360) - 180;
        if (Math.abs(netLon) <= 90) {
          const xFactor = Math.sin((netLon * Math.PI) / 180);
          ctx.beginPath();
          ctx.ellipse(cx, cy, Math.abs(R * xFactor), R, 0, 0, Math.PI * 2);
          ctx.strokeStyle = 'rgba(100, 116, 139, 0.18)';
          ctx.stroke();
        }
      }

      // Latitude Grid Lines (Parallels)
      for (let lat = -60; lat <= 60; lat += 30) {
        const latRad = (lat * Math.PI) / 180;
        const yPos = cy - R * Math.sin(latRad);
        const latRadius = R * Math.cos(latRad);
        ctx.beginPath();
        ctx.moveTo(cx - latRadius, yPos);
        ctx.lineTo(cx + latRadius, yPos);
        ctx.strokeStyle = 'rgba(100, 116, 139, 0.14)';
        ctx.stroke();
      }

      // Draw craters with exact orthographic projection
      features.forEach(f => {
        const netLon = ((f.lon + currentAngle + 540) % 360) - 180; // in [-180, 180]
        if (Math.abs(netLon) < 88) { // Visible on front hemisphere
          const lonRad = (netLon * Math.PI) / 180;
          const latRad = (f.lat * Math.PI) / 180;

          // Projected crater center
          const px = cx + R * Math.cos(latRad) * Math.sin(lonRad);
          const py = cy - R * Math.sin(latRad);

          // Foreshortening factor = cos(angular distance from disk center)
          const cosDist = Math.cos(latRad) * Math.cos(lonRad);
          if (cosDist > 0.02) {
            const baseR = R * f.r;

            // Direction from disk center to crater center
            const dx = px - cx;
            const dy = py - cy;
            const dist = Math.hypot(dx, dy);
            const rotAngle = dist > 0.001 ? Math.atan2(dy, dx) : 0;

            const semiMinor = baseR * cosDist;
            const semiMajor = baseR;

            ctx.save();
            ctx.translate(px, py);
            ctx.rotate(rotAngle);

            if (f.main) {
              // Highlighted tracked crater
              ctx.beginPath();
              ctx.ellipse(0, 0, semiMinor, semiMajor, 0, 0, Math.PI * 2);
              ctx.fillStyle = 'rgba(2, 132, 199, 0.22)';
              ctx.fill();

              ctx.strokeStyle = '#0284c7';
              ctx.lineWidth = 6;
              ctx.stroke();

              // Center peak
              ctx.beginPath();
              ctx.ellipse(0, 0, semiMinor * 0.25, semiMajor * 0.25, 0, 0, Math.PI * 2);
              ctx.fillStyle = '#0284c7';
              ctx.fill();
            } else {
              // Background crater
              ctx.beginPath();
              ctx.ellipse(0, 0, semiMinor, semiMajor, 0, 0, Math.PI * 2);
              ctx.fillStyle = 'rgba(71, 85, 105, 0.12)';
              ctx.fill();

              ctx.strokeStyle = 'rgba(71, 85, 105, 0.45)';
              ctx.lineWidth = 3;
              ctx.stroke();
            }

            ctx.restore();
          }
        }
      });

      ctx.restore(); // Remove sphere clipping

      // Outer Rim Glow / Outline
      ctx.beginPath();
      ctx.arc(cx, cy, R, 0, Math.PI * 2);
      ctx.strokeStyle = '#475569';
      ctx.lineWidth = 4;
      ctx.stroke();
    }

    function setAngle(angle, animated = false) {
      if (animated) {
        targetAngle = angle;
        if (!isAnimating) {
          isAnimating = true;
          requestAnimationFrame(animateStep);
        }
      } else {
        currentAngle = angle;
        slider.value = angle;
        draw();
        updateButtonStates();
      }
    }

    function animateStep() {
      const diff = targetAngle - currentAngle;
      if (Math.abs(diff) > 0.3) {
        currentAngle += diff * 0.16;
        slider.value = currentAngle;
        draw();
        requestAnimationFrame(animateStep);
      } else {
        currentAngle = targetAngle;
        slider.value = currentAngle;
        draw();
        isAnimating = false;
        updateButtonStates();
      }
    }

    function updateButtonStates() {
      if (Math.abs(currentAngle) < 10) {
        btnCenter.classList.add('active');
        btnEdge.classList.remove('active');
      } else if (Math.abs(currentAngle) > 55) {
        btnEdge.classList.add('active');
        btnCenter.classList.remove('active');
      } else {
        btnCenter.classList.remove('active');
        btnEdge.classList.remove('active');
      }
    }

    // Slider input
    slider.addEventListener('input', (e) => {
      isAnimating = false;
      setAngle(parseFloat(e.target.value), false);
    });

    // Preset buttons
    btnCenter.addEventListener('click', () => {
      setAngle(0, true);
    });

    btnEdge.addEventListener('click', () => {
      setAngle(72, true);
    });

    // Direct Drag interaction on canvas
    canvas.addEventListener('pointerdown', (e) => {
      isDragging = true;
      isAnimating = false;
      startX = e.clientX;
      startAngle = currentAngle;
      canvas.setPointerCapture(e.pointerId);
    });

    canvas.addEventListener('pointermove', (e) => {
      if (!isDragging) return;
      const dx = e.clientX - startX;
      const sensitivity = 0.5;
      let newAngle = startAngle + dx * sensitivity;
      newAngle = Math.max(-80, Math.min(80, newAngle));
      setAngle(newAngle, false);
    });

    canvas.addEventListener('pointerup', (e) => {
      isDragging = false;
      try { canvas.releasePointerCapture(e.pointerId); } catch (_) {}
    });

    canvas.addEventListener('pointercancel', () => {
      isDragging = false;
    });

    // Initial render
    draw();
  </script>
</body>
</html>

science.ks3.y1.t4.s3

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