The rapid flickering or twinkling of stars caused by turbulent cells in Earth's atmosphere that act like moving lenses, continuously changing the star's apparent brightness and position. Planets scintillate less due to their larger apparent size.
From Latin 'scintillare' meaning 'to sparkle' or 'emit sparks', adopted in the 17th century to describe stellar twinkling. The scientific understanding of atmospheric turbulence as the cause developed in the 20th century with advances in fluid dynamics.
Scintillation is why we can tell planets from stars with the naked eye! Stars appear as point sources and twinkle rapidly, while planets show tiny disks that average out the atmospheric turbulence, appearing steady - it's a natural way to distinguish between stellar and planetary objects.
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