Stars twinkle because they are moving or flickering with light.
Stars appear to twinkle because of atmospheric distortion, Earth's atmosphere acts like a lens, bending starlight randomly as it passes through turbulent air layers. Stars don't actually twinkle; it's purely an optical effect of our atmosphere. Planets, being closer, appear stable because their light spreads across more of the atmosphere.
Reception
Sources
- Stellar Scintillation - NASA PRIMARY
- Snopes: Star Twinkling REFERENCE