Aristotle reasoned that stars twinkle because people need to stretch their vision to see them, and that vision wavers. Centuries later, scientists guessed that stars spin like diamonds, twinkling as they turn through different facets. It wasn't until the early 18th century that Isaac Newton determined Earth's atmosphere was to blame. The question was how. Today, the generally accepted explanation is "stellar scintillation." Lome Whitehead, a physicist at the University of British Columbia, describes it like this: A bright light, positioned far away, projects as a tiny point through the varying air densities of our atmosphere. Hundreds of these pockets act as lenses, refracting the light so that it moves like the light on the bottom of a swimming pool on a sunny day. The changing swells on the pool's surface correspond to the turbulent shifting of our atmosphere.
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