Why do some stars appear to twinkle in the night sky?
Quick Answer
Stars twinkle because Earth’s atmosphere bends their light unevenly as air moves and changes temperature. Their light source is so small that the distortion is easy to notice.
The Full Story
Starlight passes through layers of moving air with different densities, temperatures, and humidity. This turbulence bends the light slightly in constantly changing directions, making a star seem to shimmer or twinkle. Planets usually twinkle less because they appear as tiny disks rather than point sources. Astronomers call this atmospheric scintillation, and it is one reason observatories are built on high, dry mountains. The effect is strongest near the horizon, where light passes through more atmosphere.
Key Facts
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Suggested video title for this topic:
"Why do stars seem to sparkle?"